The Display of the Siamese Fighting Fish, Betta splendens

VOLUME

1968·CONTENTS

ANIMAL BEHAVIOUR MONOGRAPH S EDITORS

J. M. CULLEN OXFORD

C. G. BEER NEWARK, N.J.

LONDON BAILLitRE, TINDALL &

CASSELL

M. J. A. SIMPSON

The Display of the Siamese Fighting Fish, Betta splendens

N. G. BLURTON JONES

Observations and Experiments on Causation of Threat Displays of the Great Tit (Parus major)

1s

JANE VAN LAWICK-GOODALL

The Behaviour of Free-living Chimpanzees in the Gombe Stream Reserve

161

Part 1

Vol. 1

1968

The Display of the Siamese Fighting Fish,

Betta splendens M. J. A. SIMPSON Sub-Department of Animal Behaviour, Madingley, Cambridge Present address: Department ofPsychiatry, The London Hospital Medical College, Turner Street, London El

I.

INTRODUCTI ON

1

2.

METHODS

5

3. UNITS OF BEHAVIOUR RECOGNIZED IN THREAT DISPLAY

4. SEQUENCES AND RELATIVE FREQUENCIES OF MOVEMENTS IN ONE FISH'S DISPLAY

8 18

5. SECOND BY SECOND INTERACTION OF TWO DISPLAYING FISH

23

6. AN ENCOUNTER BETWEEN TWO FISH

37

7. VARIATION IN THE DISPLAY FROM INDIVIDUAL TO INDIVIDUAL ..

46

8. SUMMARY AND DISCUSSION OF RESULTS ..

55

9. REVIEW OF METHODS FOR STUDYING DISPLAYS

61

10.

SUMMARY

69

REFERENCES

71

EDITORIAL This journal, Animal Behaviour Monographs, has been launched to encourage several different types of long article. The first type consists of accounts of substantial descriptive studies of behaviour. For a variety of reasons they are unpopular with editors who have to handle a large number of manuscripts and who have limited space in which to squeeze the acceptable ones. Furthermore, they are, without much justification, unfashionable, having been displaced by short reports of experimental studies. The control of the con­ ditions that affect behaviour is an obvious goal, but a great deal of time is wasted in manipu­ lating or measuring irrelevant variables in an experimental set-up. One of the virtues of looking at animals in unrestricted environments is that the observer becomes aware of the context in which particular patterns of behaviour occur. In this way hypotheses abo"tJt the conditions necessary for the occurrence of those behaviour patterns and the events which bring them to an end arise from the observations. It is important that such work should be encouraged and, what is more, published. The second type of article consists of a series of interrelated experimental studies which could be published as separate papers but which would greatly lose their impact if they were. Some authors will feel disinclined to flout the ludicrous standard which measures professional ability in terms of the numbers of papers published. However, they should bear in mind that the coherence of an extended piece of work can be lost if it is broken up for the purposes of publication; furthermore, a monograph has a durable value which shorter papers rarely have. A hybrid between the first and second type of article is also envisaged. A group of linked experimental studies often develop from observations made on animals in natural or, at least, relatively unrestricted environments. We have already argued that such observa­ tions should be published and we should particularly like to encourage monographs that incorporate both the inductive and the analytical phases of a research project. Finally, Animal Behaviour Monographs will publish critical reviews of particular areas of research. The general need for periodic surveys is too well known to require justification here. However, the opportunities for publishing surveys of parts of the literature on be­ haviour are limited. Usually the author is required to cover so much ground that he must, of necessity, be superficial, or he must be so succinct that he is unable to develop his argu­ ments at any length. The specific need for articles which deal with a circumscribed part of the animal behaviour literature will, we hope, be met by the Journal. In order to give Animal Behaviour Monographs the widest possible circulation the journal is supplied free to the members of the Association for the Study ofAnimal Behaviour and the Animal Behavior Society; it is sold at moderate cost to subscribers. Initially three monographs will be published each year and grouped into volumes of between 300 and 500 pages. Some notes on preparing monographs are given on the inside of the front cover. But, in any event, potential contributors are asked to contact one of the Editors.

A male Siamese fighting fish, Betta splendens, displaying (Professor T. I. Thompson)

Animal Behaviour Monograph, 1, 1

1. INTRODUCTION a fish turns to face a partner which is facing already, that partner turns broadside almost at once. On a longer time scale, an increase in the violence of one fish's display, in terms of tail beating, or biting, seems to be paralleled by an increase in the violence of the other's display, although Braddock & Braddock (1955) found that in twelve pairs fighting longer than an hour, the winner-to-be raised its gill covers and bit twice as often as its partner. This last difference between the displays of the participants was the only one known to me before I began the work described here, although it is likely that other differences in display and fighting are known to those who bet on the outcomes of fights staged in the bars of Bangkok. In many ways the en­ counters are similar to those of cichlid fish described by Oehlert (1958) and Lorenz (1966), and those of Badis badis described by Barlow (1962b and 1963). From the foregoing discussion, it can be seen that a criterion for a successful description of the threat display is the pre­ diction of the outcomes of encounters from the differences between the displays of the par­ ticipants. If the display of one fish is regarded as experience for the other, then the display situ­ ation is potentially useful for studying the wider issue of the relation between a subsequent and stable change in behaviour (such as the cessation of display by the loser) and the preceding events during the fish's encounter with its partner. This approach is analogous to the Skinnerian one of describing a change in a rat's behaviour towards the lever in its cage, which 'responds' to the rat's behaviour in certain pre-arranged ways. But in the case of the fish, the observer must discover the schedules underlying the inter­ action. Moss (1967) takes this approach in interpreting his observations on the changes in the behaviour, over the first 3 months, of human infants and their mothers, in terms of their interaction during this time, which is described in terms of the frequencies of certain responses

This monograph attempts to describe the threat display of Betta splendens. So easily is the display elicited in domesticated male fighting fish, and so similar are its component moves from one time to another in the same fish, and from fish to fish, that such a description might seem to be a trivial aim. However, the displays of domesti­ cated males are rarely allowed to run their course, for fear of the resulting damage; so that it has not been possible to discover whether differences between the displays of the participat­ ing individuals are correlated with the differences in the outcomes for those individuals, with one winning and the other losing. The possibility that the displays could differ in the frequencies, sequences and tempos of their component stereo­ typed moves has only recently been considered (Laudien, 1965 and Clayton & Hinde, in press). Braddock & Braddock (1955) showed that en­ counters between pairs of female Betta splendens can have different outcomes for the participants, with one of the fish stopping its display first. If there are also differences between the fore­ going displays of the two participants, a co­ herent description of the threat display should aim at relating the outcome to the preceding displays. Braddock & Braddock (1955) isolated the females for 7 days before introducing them to each other. The ensuing display and 'fight' (defined as behaviour involving rapid exchanges of bites) lasts for as long as an hour in some fish, but usually for 30 to 45 min. The encounter ends when one of the pair ceases to display and begins to avoid the other, after which the other fish soon stops to display too, and begins to follow and chase the first. Eventually the fish separate and begin to explore, and if they meet again in the container where the encounter was staged there is little display, and the loser is usually the first to move away (chapter 6). While displaying during these encounters, each fish seems to follow the changes in its partner's behaviour moment by moment. For example, almost every time 1

2

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

by one partner (such as ceasing to cry when picked up) to the other's behaviour (such as picking up). He explains differences in the mother's behaviour to 3-month-old boys andgirls in terms of the differences in their experience, with the boys ceasing to cry less often than the girls. Such studies lead to the deliberate arrange­ ment of schedules (e.g. by Rheingold, Gewirtz & Ross, 1959). This approach is also illustrated in chapter 8 of this monograph. It may seem surprising that studies like this one are not attempted more often. However, there are recording difficulties (chapter 2), and certain aspects of ethology's tradition may dis­ courage such an approach. Ethology has been preoccupied with the question of what starts (or 'releases') a pattern of behaviour, and with questions of the behaviour pattern's function and survival value. In connection with the first preoccupation, the ways in which the behaviour patterns resemble each other from occasion to occasion, and from animal to animal, have been emphasized (e.g. by Heinroth, 1911 and Lorenz, 1950), and the striking stereotypy of certain display movements (e.g. Betta splendens pelvic fin behaviour, described in chapter 3) distract from the possibility that the sequences and relative frequencies of such movements may vary, even when the stimulus situation seems to stay the same. However, Heiligenberg (1963) found such variation in cichlid displays, and Marler & Hamilton (1966) emphasize the need for careful description of the temporal patterning of behaviour patterns. If the frequency of a display movement in a constant situation varies, it is likely that the responsiveness of an animal, in terms of that movement, to a particular move by its partner, may also vary. This monograph describes methods both for analysing temporal patterns of behaviour, and for measuring re­ sponsiveness of individuals in terms of particular display components in free-running situations. The dramatic way in which sequences of be­ haviour have been shown to be released by certain stimuli (e.g. Lack, 1939 and other examples in Tinbergen, 1951) suggests such a

simple model of the way in which the behaviour of one animal can alter that of another in the course of an interaction that the task of analysing such an interaction does not seem very challeng­ ing, or likely to show anything unexpected. Sometimes interactions may indeed be as simple as the model suggests. Thus Schein & Hale (1965) showed that any one of the successive responses of a turkey hen, by which she cooperates when a turkey cock mates with her, may be elicited by suitable stimuli provided by the human hand, so that the interaction can be described in terms of the effect of relevant moves by the cock on the hen's behaviour. But if one of the participants in an interaction does not respond to the other's movements every time, then the question of how often it does respond becomes an interesting one, because differences in responsiveness may have different consequences for the later be­ haviour of both animals. Ethology's second preoccupation, with func­ tion, may also have restricted the studies of interaction, by tempting ethologists to lend un­ due weight to those interactions which fulfill their presumed functions 'successfully' in the final description of the behaviour. Thus a description of courtship behaviour may draw heavily upon the courtship episodes ending with the fertilization of eggs, and ignore the episodes with other outcomes. Although such descriptions provide essential enumerations of the component moves, they tend to be idealized as though courtship really did 'run smooth' if the observer could arrange the conditions suit­ ably. But if courtship studies used the episodes with other outcomes, such as the male chasing the female away, or vice versa, relationships between the particular outcomes and the pre­ ceding patterns of interaction could provide starting points for fruitful studies. In this con­ text, it is relevant that all the moves in Betta splendens threat display also occur in its court­ ship, and neither the threat nor the courtship displays will be fully understood before both have been studied (Kiihme, 1963).

INTRODUCTION

Although chapter 9 of this monograph con­ siders ethologists' interpretations of display in terms of 'conflicts' between 'tendencies' to attack and to flee, 'aggression' as an abstract concept is not discussed. The reader may decide for himself whether to regard Betta splendens' threat display as an aggressive one. So many patterns of behaviour are classed as aggressive that the category is no longer likely to be a very useful one. Thus behaviour has been classed as aggressive by its function, such as the defence of territory (but note the above-mentioned limit­ ations of a functional approach), by its conse­ quences, such as pain or injury (e.g. Dollard et al., 1939; Jackson, 1954; Berkowitz, 1963; Buss, 1966), and by its causes (Scott, 1966), including frustration (e.g. Buss, 1966). Many studies of ag­ gression fail to define independent variables operationally, as Kaufman (1965) has shown. Moreover, the aggressive behaviour of different animals has been studied from different points of view. Only the rat's aggressive behaviour has been studied from a wide range of standpoints. For the function of wild rats' aggressive be­ haviour see Barnett (1963), for behaviour studied by its consequences-mouse killing-see Myer & White (1965), for its causes, such as the situ­ ations arising in semi-natural situations, see Barnett (1963) and Scott & Fredericson (1951), and for pain as a cause of rat aggression see Ulrich (1966). A review of aggressive behaviour that distributes its attention between the methods and species described in a way corresponding to the distribution of research done has yet to be written. The extant accounts of examples of animals' aggressive behaviour buttress their authors' views of (Ardrey, 1967), and hopes for, (Lorenz, 1966*) human behaviour, but do not refer to current research on human aggressive behaviour (e.g. by Berkowitz, 1963 and Buss, 1966). The present study uses the threat display as an example of a complex pattern of behaviour, which can be modified both on a short- and a long-time scale by another equally complex *See Barnett (1967) for a useful criticism.

3

pattern. A priori, the subject matter of this monograph is unlikely to have any direct cor­ respondence with the studies of aggression mentioned above. Moreover, this monograph focuses on the changes occurring during the interaction, and the 'independent variables' of this work have been the partner's display changes. In contrast, the majority of studies of aggressive behaviour (especially that in which dominance­ subordination relations are established) associate outcome with events and conditions established before the interaction takes place. Certain special problems accompany an attempt to study an interaction where the par­ ticipants affect each other moment by moment, where there are parallel changes in the partners' displays during the encounters, and where the outcome for the two individuals is different. Differences between the individuals' displays may lie in the responsiveness of certain display actions to particular actions of the partner. Chapter 5 studies the moment to moment interaction from this point of view; a study of how one fish alters the other's display second by second obviously requires that the pattern of the individual's display should be described in terms of the sequences and relative frequencies of the com­ ponent actions (chapter 4), and this in turn demands that the component moves should be distinguished from each other (chapter 3). By comparing the displays of winners and losers, aspects of display related to success in an encounter can be isolated (Braddock & Braddock, 1955, and chapter 6 in this monograph). How­ ever, because the animals are interacting in a free-running situation, where each can affect the other, it is also necessary to use a display­ eliciting situation such as a stationary puppet, which the fish cannot influence, because in the situation with two live fish, each animal's display reflects that of its partner. If the displays of several fish to the same puppet are compared, it becomes possible to analyse the variation in display from fish to fish, more effectively than in a situation where the fish are merely classed as winners or losers, for in the presence of a puppet,

4

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

the fish can be scaled according to the propor­ tion of the test they spend near it, and correlated variations in the display can be sought. From such variation it may be possible to predict success in an encounter. If the fish affect each other second by second, and yet their display lasts for minutes, the

question of whether the display at any one moment depends only on events in the last few seconds, or also on earlier events, arises; and this leads to the question of how complex the fish's C.N.S. must be to integrate the preceding events in the fish's own, and its partner's display. Such questions are discussed in chapter 8.

2. METHODS Clayton (personal communication) found that fish that were light coloured and/or primarily single-coloured raised their gill covers (15) less frequently during 11 days in the presence of their mirror images than did dark fish. Table XI, in chapter 7, suggests that blue fish are more ready to display at a stationary puppet than are crimson-maroon ones; and blue fish attack hand-held Plasticine models most readily in class-room demonstrations.

Subjects

The subjects of the observations and experi­ ments described in this monograph were adult domesticated Betta splendens. Most of the fish were bought from London dealers, but some had been bred at Madingley. The fish used in the experiments were at least 4 months old, as judged by comparing them with those bred at Madingley, and they were mature. (Males usually build their first nests in, or before, their 3rd month.) Although domesticated Bettas may live for 2 years, none was used in an experiment after its first year, for by this time they become slightly sluggish.

The forms of the display movements, as op­ posed to the frequency of their occurrence, were rather constant, and independent of the fish's colour, or of whether it was a wild or domesti­ cated one.*

The taxonomy of the wild-type Betta splendens has been described by Regan (1909), and its colour and patterning are described by Regan, Cantor (1849) who calls it Betta pugnax, and by Smith (1937). Domesticated fish show great variety in colour and pattern, in contrast to the wild fish, and domesticated male fish may lack some or all of the following features of the wild fish: white tips to their pelvic fins, bright nacreous blue-green streaks between the rays of dorsal and caudal fins, similarly bright patches in the 'irises' of their eyes, and black bars across the dorsal fin rays. Betta splendens has been domesticated in Europe and the U.S.A. since the mid-1920s (Innes, 1949). Harvey & Hems (1952) describe some of the colour varieties. According to Smith (in a letter, part of which is reproduced in Innes, 1949) there is a short­ finned fighting breed in Bangkok, used in fights, on which wagers are made, and losers are never used for breeding.

Male and female domesticated fighting fish could share the same tanks and did not fight severely enough to cause fin tears more than 1 mm long (which heal in 2 days) if they had been together since hatching, or if they were put to­ gether in the same tank before they were 90 days old. Even after this age, females and wild-type fish strange to each other could often be placed together and cause each other little damage in their initial displays, but domesticated males that were strange to each other usually caused more damage. Four to five adult females were kept in a tank, while adult domesticated males were usually kept separately, sometimes in whole or sometimes in half tanks. The tanks were 24 in. long, by 12 in. wide and they were filled to a depth of 8 in. so that each held about 8·7 gal, or 39·4 I., of water. Once a male was destined for an experiment, care was taken to prevent it from seeing other fish. (However, see also the experiment described in chapter 7.) A tank for two fish was divided by an opaque partition of unplasticized Perspex, and the neighbouring fish were prevented from seeing each other by internal reflection in the tank's glass walls past the edges of the partition.

In the experiments described in chapters 6 and 7 of this study the colours of the fish used are specified in Tables V and XI respectively. The male fish providing data for the analyses in chapter 5 were red. In future work with Betta it will be advisable to specify the subjects' colours. Albino fighting fish display little, if at all (Lissmann, 1933 and Noble, 1939), and

*The Bangkok Department of Fisheries kindly collected the wild-type Betta splendens for me.

5

6

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

(2-in. strips of black polythene were placed inside the tanks where the partition met the glass walls.) The object of such isolation was to avoid a reduction in the fishes' responsiveness to display-eliciting stimuli. But males kept com­ pletely isolated may become less active and brightly coloured than those given regular short opportunities to display, and a better policy might be to allow the fish about 2 min of display every day, as do Hogan and Burnell (both personal communications). Cambridge tapwater was used (pH 7 ·4, no free chlorine, and hardness 130 to 150 ppm). It was not aerated (the fish breathe air). About i\th of a tank's volume had to be added weekly to replace loss by evaporation, in spite of glass plates resting on top of the tanks to minimize this loss, and to exclude dust. (The plates were raised an inch at their ends to allow air to cir­ culate.) The tank's temperature was thermo­ statically held at 26·7 ± 1°C (i.e. 80 ± 2°F). * Apparatus and partitions were made of un­ plasticized Perspex and sometimes of Paxolene (a resin bonded paper). Black strips of polythene were used to prevent internal reflections, and black polythene was also used to exclude light on the dark side of the one-way mirror (p. 28). (This mirror was chromed and provided by Whilems Ltd.) Heating wire was wound onto Formica frames, and insulated with Araldite. The floors were covered with gravelly sand, and flower pots (on their sides) and stones were placed in some of the tanks. (Holes in flower pots must be blocked to prevent inquisitive fish from being trapped by their gills). Tanks not used for experiments were planted with Vallisneria spp. and Riccia sp., and Cerato­ phyllum sp. were brought in from local ponds for temporary dense cover in communal and breeding tanks. *The temperature at which the fish are kept during experiments should be controlled as accurately as possible. Whether the fish build nests or not (Goodrich & Taylor, 1932), how frequently they take air (Liss­ mann, 1933), and how ready they are to display to a standard display-eliciting stimulus (Hess, 1952) are all affected by changes of as little a 2°C.

Planorbis corneus and Physa sp. snails flour­ ished in all the tanks. The former removed algae from the glass walls, and both scavenged the floors for uneaten food and sometimes for decaying weed. The room lights (fluorescent strip lights) were turned off for 12 hr at night, but in summer the fishes' nights were shorter than 12 hr, be­ cause the windows were not curtained. Food Live Tubifex worms were added to petri dishes in the tanks about four times a week, so that food was available to the fish all the time. From local ponds live Chaoborus sp. larvae, Daphnia sp. and Chironomus sp. larvae were usually obtained twice weekly. Enchytreus albidus (whiteworms) were fed to the fish once or twice a week. Handling and Apparatus The tanks already described were used for the experiments, but they were always cleaned before being used thus. The contents of the tank were stirred violently, whereupon the 'mulm' settled after the sand and could be siphoned off with the water. This process was sometimes repeated, and the tank was finally filled, and allowed to stand at least 24 hr before the experiment. To move a fish to another tank, it was first coaxed into a transparent food container and then carried over to the appropriate tank. With practice the fish could be moved without letting them inadvertently touch any solid surface. Damage and Disease Fin tears usually healed within 3 days, whether treated (by leaving the fish in a dilute salt solution, as described by Innes, 1949) or not. Fish that became dull and sluggish overnight, or that showed nematode worms (such as Camal­ lanus sp.) or tapeworms protruding from their anus were not used in experiments. The Recording Technique A ten-pen time-event moving paper recorder, made by Cambridge Consultants, was used for

METHODS

recording the display. Such actions as tail beats and bites, which were over in an instant, were recorded by means of a quick press of the corresponding pen. For actions like turning to face, which was followed by at least 1 sec, and usually 3 or 4 sec of the facing posture, the 'turning to face' key was held down for as long as the fish continued to face. Thus the records preserved information about durations as well as frequencies of activities. The accuracy of the records for the observa­ tions described in this monograph was not limited by the properties of the recorder. One pen can show as many as four separate marks on the fo th of an inch that the paper moves each secoiid. The pens were checked for alignment, so that when they were activated at the same moment, they all wrote at the same point along the paper. The ability of the observer is, however, likely to limit the accuracy of the records. I made no direct study of my ability at recording. (A suit­ able method would be simultaneously to film and record the same sequence of behaviour, and to compare the results of the two methods.)

7

But pilot experiments recording single fish displaying to their mirror images gave a total of at least 150 hr recording experience, and thereafter recording did not seem particularly difficult. The events to be recorded are clear-cut, and sharply defined in time; there is considerable redundancy* in their order of occurrenc6, and even when two fish are displaying there are only ninety changes per minute to record. When two fish are being recorded, it is the nearly simul­ taneous events requiring decisions about their order of occurrence that raise the greatest diffi­ culty. An obvious source of bias would be the greater attention being given to the fish recorded with the right hand than to that recorded with the left hand, and the method of avoiding this was to assign some of the movements of each fish to the fingers of each hand. Even when each fish had a hand (chapter 6), the experiment was effectively blind, since the observer did not know in advance which fish was going to win the encounter. *Seep. 22 for the patterning of the display. For example, a facing fish can only bite, or tum broadside, and a broadside fish may flicker its pelvic fins or beat its tail, and tail beating usually follows fin flickering.

3. UNITS OF BEHAVIOUR RECOGNIZED IN THREAT DISPLAY Before the display is analysed into its component movements, an encounter between two subjects is described to provide a reference description of a whole display, because it is all too easy to lose stght of the display as a whole in the detailed analyses of particular aspects of it that constitute the bulk of this monograph. The picture that the first section of this chapter attempts to provide can also be obtained by reading Brad­ dock & Braddock's {1955) descriptions. The following account is based on a polygraph record of the interaction of two domesticated female Bettas that had never seen each other before.

it noticed the first fish. Over the next 3 sec, both fish darkened so that their longitudinal stripes were almost obscured, and they closed up to within a fish-length of each other. The first fish then spread its gill covers for a second time, and it turned to face the second, withdrawing both its pelvic fins so that they lay along its belly. The second fish remained broadside to its facing neighbour, and extended the pelvic fin nearest its neighbour so that it pointed downwards (as in Fig. 2b). The first fish faced for a second, and then it turned broadside, lowering its gill covers and re-erecting its pelvic fins as it did so. At once the second fish turned to face the first, raising its gill covers and withdrawing its pelvic fins as it did so, whereupon the first flickered the pelvic fin on the offside to and fro. In the 10 sec of the encounter that elapsed, both fishes' backs and heads had become almost jet black, and the greens and blues on their scales, eyes and fins were brighter. Over the next 30 sec the fish continued to alternate facing (and raising their gill covers as they faced) with turning broadside {when they also lowered their gill covers), and while it was broadside, each fish usually flickered its pelvic fin and beat its tail. Sometimes both were broad­ side at the same time, and then they usually beat their tails at each other. In general, the fish faced each other in turn, although the first fish once faced the second twice in succession while the second stayed broadside. Often, just before one of the fish turned to face, it quickly closed and opened the rays in its tail, so that the tail was shut and opened like a fan (tail flash­ ing, p. 16). On two occasions when one of the fish was facing its broadside partner, the facing fish turned until the two were in a tail-to-head carou­ sel position, and then they held their mutual positions very rigidly as they rotated-using only their rapidly beating pectoral fins. Some­ times one of the fish moved its head nearer the other's tail, whereupon the other flashed its tail,

Description of a Threat Display One of the most striking features of such a display is the 'single-mindedness' with which the fish interact with each other. One of the pair may break off to threaten a third intruder, but it will quickly return to resume the main display with its original partner. Moreover, the display between two strangers starts within seconds of their introduction to each other. Only after one of the fish has 'given up' do they begin to feed, explore etc., and their subsequent interactions are relatively brief. For example, if they come within a fish-length of each other, it is usually the loser that moves away first-after the other has moved about 1 mm towards it, or merely turned to face, or perhaps only turned its eyes towards it. Both fish, at the beginning of the encounter to be described here, were rather dull-coloured, with faint longitudinal stripes on their bodies (p. 15). Within 2 sec of being placed in the tank, where they were to interact, one turned towards the other, spread its vertical fins, then briefly spread its opercula and extended the black brachiostegal membranes that otherwise lie behind (gill cover erection, p. 15 and Figs Id, 2 & 3). The first fish then began to approach the other, which was moving along slowly, but which checked and spread its own vertical fins when 8

UNITS OF BEHAVIOUR IN THREAT DISPLAY

and the first moved its head away again. Such carousels lasted 10 to 15 sec. The second carousel ended when one of the fish broke away and went up to the surface to gulp air. The other also came up, and they both took air together (see also Lissmann, 1933 and Smith, 1937). During the display such simultaneous air gulping was repeated approx­ imately every t min. At the end of the 1st min, the two paraded round the tank, side by side, each crowding and beating the other with its tail and caudal peduncle. Finally one of the fish turned to face the other, whereupon the other beat its tail even more frequently for a moment before turning to face too. Then the fish that had first turned to face turned broadside again, and beat its tail at the other which stayed facing for a few seconds. For the next 7 min the fish continued thus, facing each other in turn, with the broad­ side fish usually beating its tail, and the bouts of gill cover erection lengthening, and the frequency of tail beating increasing, while the carousels shortened. Once, one of the fish faced the other twice before the other turned to face again. Soon after their 7th min of display, one of the fish, that was facing its partner's head, opened its mouth as if to bite, but did not attempt to drive the bite home until it was facing its partner's tail. As it closed in to bite, its partner beat its tail hard and accelerated round, thus evading the first fish's bite and attempting to bite its tail, The first fish, however, was moving forwards, and each flashed past the other's tail. Three more sequences of biting, tail beating, and bite evasion followed before one of the fish showed a tear in its tail. In these rapid manoeuvres the vertical fins were held less rigidly erect than they had been at the start of the display. Mutual biting attempts were well separated by the pre­ viously described mutual gill cover raising and tail beating. It is seldom easy to foresee the end of such a display. One fish ceases to display before the other, its fins slacken, and it starts to swim

9

away from its still displaying partner. At first the partner seems to moderate its own display, as if to avoid discouraging the first fish from continuing. Finally the partner stops too, and begins to chase the first, which soon pales and shows longitudinal stripes. During the chase the pursuer may direct nips towards the loser's caudal and anal fins. It was difficult to make generalizations about the display before it had been analysed. In the sentence 'Der Kampf der Betta ist das Frage- und Antwortspiel zweier aufeinander abgestimmter Subjekte', Lissmann (1933) gives a vivid im­ pression of the interaction. Braddock & Brad­ dock (1955) describe the aggression shown as 'equal and mutual'. Oehlert (1958) describes how fights between cichlid fish go through a number of distinguishable stages-with an early stage consisting mainly of tail beating preceding a stage with biting, as in Betta. But in Betta the stages are not so clearly separate as they are in the descriptions of cichlid displays, and the fish often revert to an earlier stage quite late in an encounter. It is difficult, just by watching an encounter, to recognize any invariable responses by one of the fish to particular actions by the other, and it soon becomes clear that the be­ haviour of neither fish seems to be 'driven' by that of the other. Units of Behaviour Recognized This section describes the orientations, move­ ments and postures that are the units of the subsequent analyses. So far as possible, these 'units' are distinguished by the forms of the movements made by the fish, rather than by their effects on the fishes' environments. Thus 'tail beating by two broadside fish' is preferred to 'jockeying for position'. It is often surprisingly easy to erect criteria for distinguishing the units since they involve combinations of orientation and posture repeated more often than would be expected by chance. (Of course it is by such regularities that someone becoming familiar with the behaviour of an animal comes to recog­ nize distinct actions before being able to say

10

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

how he does so.) 'Turning to face' is an example of an easily distinguished unit. A facing fish not only has a particular orientation with respect to its partner, but also withdraws both its pelvic fins so that they lie along its belly. Of course there are many units that have to be defined arbitrarily. An example is 'near the partner', defined as within a fish-length of the partner. But this criterion is easy to apply because a fish either displays very near its partner, or other­ wise well away, and its approaches and retreats are usually fast. This section also describes the movements usually performed by Bettas in the early stages of their courtship (i.e. in those interactions that lead to egg laying in the female) because the threat display and courtship share many actions, and it is unlikely that either will be fully under­ stood until both have been studied in equal detail.* Betta's display is so well suited to the record­ ing of its visible components that its other aspects have been neglected in this study. For example, the frequency with which the trans­ parent pectoral fins beat varies widely, but this can only be recorded by watching closely and exclusively. In the early stages of a display the frequency of air gulping changes (Laudien, 1965), and air gulps may produce sounds with signal function. Moreover, the amplitude with which fish beat their tails varies widely from occasion to occasion and from fish to fish, and the effects of the tail beats must vary correspondingly. But all tail beats have been recorded as alike in this work.

Non-display Activities The frequencies of all these activities may change when the fish is in a situation where it is likely to display, or when it is actually dis­ playing. Adult domesticated fighting fish gulp air approximately every minute when they are kept • More details of courtship are to be found in Ktihme (1963), and in notes deposited at the Sub-Department of Animal Behaviour, Madingley, Cambridge.

at 27°C in still water. In deoxygenated water they can obtain their whole supply thus (Liss­ mann, 1933). During display the two fish often synchronize their air gulping. A fish that makes periodic visits to a place where it displays 1s especially likely gulp air before it sets out on a visit to display, and if the bubbles thus made stay on the surface long enough, they may form the focus of a bubble nest. In air gulping, the 'used' air is usually passed out through the opercula as new air is taken in through the mouth. Some­ times large bubbles are released through the opercula, especially in nest building, and also when the fish is carrying for eggs and young in the nest, when such bubbles released under­ neath it may provide oxygen. Betta feeds on bottom-living worms in the way described by Lissmann (1933), and also by Barlow (1962a) for Badis badis and Tugendhat (1960) for Gasterosteus. If the worm is lying free on the substrate it is simply picked up, but if it is partly buried the fish may turn one of its sides towards the bottom as it approaches to take the worm, and then it uses its body like the claw of a hammer in withdrawing the worm-it pivots on its side, its tail thrust down and its head levered up with the worm. Betta sometimes 'stalks' free-swimming small animals,. such as Chaoborus sp. larvae, until it is a fish-head­ length from one, then the fish stops, flexes its body into a slight S, and finally darts forwards to engulf the larva. In taking more sluggish animals, such as Daphnia sp., these stages are run into each other. Sometimes, especially in the first few seconds after free-swimming food has been introduced into the tank, the fish may make darting movements without actually en­ gulfing anything. When a male fish is 'swimming vividly' (p. 12) soon after a female has been introduced to his tank, he may make darting movements indistinguishable from the above, and these may be repeated in particular parts of his tank, and the female may also make these movements as she follows the male, often in the same places.

UNITS OF BEHAVIOUR IN THREAT DISPLAY

In chafing (Tugendhat, 1960) the darting movement is similar to that made during feeding, but usually slower, and the body is always so oriented that a particular part knocks against a hard edge in the environment (such as a thermometer or a heater lead) and occasionally against the substrate, or another fish. Chafing is especially likely to occur in those places and at those times where and when an ethologist might expect the fish to be in conflict (see also chapter 9). Bites are sometimes directed at objects that are not eaten. Fighting fish sometimes bite gently at newly introduced thermometers or transparent barriers. This exploratory biting seems similar to that of Lebistes (Russell, 1967). Young fighting fish sometimes bite at the an­ tennae of snails. This could be a response to a food-like object. Adults occasionally direct violent bites (sometimes several in quick success­ ion) at snail shells (cf. Badis badis which attacks snails that intrude into its breeding burrow, Barlow, l 962c). A yawn is a more or less wide opening of the mouth and opercula, without the branchiostegal membrane being extended. It usually lasts at least a second. (For details of yawns in other species see McCutcheon, 1966.) A cough, like a yawn, starts with the opercular and mouth cavities being expanded, but both are then suddenly closed, to sharply expel water from them. (See also Baerends 1950 & Baerends­ von-Roon and Barlow, 1962a). Exploring and 'Pacing' Soon after being placed in a new tank a fish usually spends most of its time exploring, and after being left alone in the same tank for a few days some fish spend much of the time swimming round and round a particular course, such as an anti-clockwise circle near one of the walls of the tank. If the environment of such a fish is then changed, e.g. by adding a mirror, or putting another fish in view, the first fish may spend even more of time 'pacing' its tank. (For more complete descriptions in other species see

11

Hediger, 1950; Morris, 1964; Fentress, 1965 and Francis, 1966.) No qualitative study of the movements in­ volved in exploration was made. (For such a study of Lebistes see Russell, 1967. When a domesticated Betta is put into a strange tank, it swims in more frequent and shorter bouts, with fewer long bouts and long pauses, than if it had merely been removed from and returned to its home tank. When wild-type fighting fish are put into a new tank, they spend most of their first few hours hiding on the bottom before they start to explore. After being in its tank for at least a day, a fish responds differentially to such newly intro­ duced objects as a thermometer, or a piece of weed, or an ink mark on the tank wall, and it 'examines' it closely from all angles, holding its body in a C as if ready to dart away at any moment. If possible, the fish will swim round and through the new object. On their way to gulp air fish often swim a particular course, especially at night. A recently frightened fish may move up and down from its hiding place very quickly to take air, but if the cover is suitable, it may inch up to the surface and then dart down again. Wild-type male Bettas often swim steadily, with their vertical fins erect, their colours in­ tense and bright and their tails occasionally closed and opened like a fan (tail flashing). This steady swimming is to and fro along the bound­ aries of the fish's territory (as judged by its interactions with its neighbours). Domesticated Bettas do not patrol thus, but they sometimes swim to and fro along one of the walls of their tanks, flashing their tails as they do so. At no age do Bettas form schools with any recognizable structure, such as do Harengula spp. (Cullen, Shaw & Baldwin, 1965). However, when the individuals of certain large broods that have been together all their lives, are nearly adult they often seem to spend more of their time together than would be expected by chance, and such individuals bump and jostle each other

12

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

as ifthere were no 'individual distance' (Hediger, 1950). But at Madingley, where the broods were broken up into groups of four to six in their 2nd and 3rd months, the individual fish avoided each other except when they started courting, and some fish of both sexes were to be found consistently in certain parts of their tanks, which they defended against other fighting fish. Display Activities Movements of the fish with respect to their environments. An approach by one male to an­ other that has just been placed in its tank is usually rapid and direct, especially over the last few fish-lengths. During the approach, the fish's vertical fins are fully erect, except for the first few rays of the dorsal fins, which are sometimes laid back a little. The back may be humped slightly, the gill covers may be erect and the pelvic fins laid back for the whole approach, or only over the last few inches of the approach. During the approach the fish may dart or chafe, and after a number of approaches to a newly introduced female the male may begin to butt and/or bite her at the ends of his approaches. Approaches that are followed by visits as brief as 3 or 5 sec are usually followed by equally rapid retreats. After an approach (usually when the other fish is female) the male may swim rapidly away in a slightly zig-zag course, as if to show both sides of his profile to the fish immediately behind him. After each turn in the zig-zag, he may swim more slowly, and he is especially likely to check suddenly or dart immediately after a turn. He swims with his vertical fins expanded fully, and with both pelvic fins erect. Undulations passing across the vertical fins cause them to shimmer. The male may swim with shimmering fins in a smooth rather than zig-zag course. Such 'vivid swimming' (this term is also used by Bearends, Brouwer & Waterbolk (1955) describing Lebistes courtship) often takes the male all round his tank, and through the thickest weed. Zig-zag swim­ ming is especially likely to give way to vivid

swimming soon after a recently introduced female has begun to follow the male. When two males have recently been put into the same tank, they swim in a smooth deliberate manner, but they do so rather more slowly than they would in the presence of a female. A male displaying to a female from under his nest, with his head pointing up towards the nest, may undulate his body as if he were swimming in treacle, and these movements are further exaggerated when the female orientates towards him. When it is some distance from a display­ eliciting stimulus, a fish may swim slowly along at right angles to it, with rather exaggerated sinuous side to side body movements ('undula­ tions', Thompson, 1966). Almost immediately after being placed in a male's tank, a female may swim in a series of steps, her body pointed slightly downwards, and all her fins spread, but their colours not necessarily at their brightest. Her stops and starts are very clear-cut, with one to three bouts of steady deliberate swimming occurring every 2 sec. (Exploring movements are less rapid, with the fins less widely spread.) The preceding ways of moving are easily dis­ tinguished when the fish have been introduced to each other only recently, but later they be­ come 'slacker'. Thus, after some time spent courting a particular female, the male's vivid and zig-zag swimming may become more alike. At the end of an encounter between two like­ sexed fish, when one of them has begun to re­ treat from its partner, its partner follows with slack fins, sometimes nipping at the loser's anal and caudal fins. (The retreating loser also holds its fins slack.) Thereafter, the dominance-submission rela­ tion between the two fish can only be described statistically. Thus, after the distance between the two has been reduced to a fish-length or less by either (and the original loser may approach as well), it is usually the loser's movement that causes this distance to increase beyond a fish­ length again. (If they are both moving, it is

UNITS OF BEHAVIOUR IN THREAT DISPLAY

usually the loser that is moving fastest relative to the environment.) This method of measuring dominance is based on methods described by Spencer-Booth, Hinde & Bruce (1966). Orientations of displaying fish relative to their partners. When displaying fish are close to their partners and they turn to face, they withdraw

their pelvic fins as they do so* (Fig. ld, in con­ trast to le). If the gill covers are not already

13

lowered as the fish turns to face only when it is about to bite its partner. The broadside orientation is distinguished from facing by the position of the pelvic fin nearest to the partner, which is erect (Figs 2b and 2c). The other, offside, fin may be erect (2b and 2d), or it may lie along the belly (Figs 2c and 3). Transitions between the broadside and facing orientations seldom take longer than t sec, and

d

0

Fig. 1. Non-displaying (a and b), and displaying (c and d) fish. d has its gill covers erect and is facing a stationary puppet. Its pelvic fins are partly withdrawn. c, in contrast, is broadside, with the pelvic fin nearest to its partner erect. In a, the fins, as they are placed round the fish in a clockwise direction, are the dorsal, caudal, anal (also called ventral), paired pelvic fins, and one of the paired pectoral fins. b and c also show a pectoral fin, but the other figures do not, because the fins are transparent and move too rapidly for satisfactory drawings to be made from photographs. bs-the black branchiostegal membrane. o-the operculum.

erect, they are erected as the fish turns to face. If they are, they may be extended further. They are •An exception was one individual that had been reared in isolation from before the end of its first month. The positions of its pelvic fins changed little when it turned to face.

are thus quick in comparison with the 3 or 4 sec that the fish usually stays in the two orientations each time. When they are close to each other, each displaying fish alternates these two orien­ tations five to twelve times per minute. If a fish

14

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

is more than four lengths from its partner, these changes in orientation are not necessarily accom­ panied by the changes in the pelvic fin positions, and are thus not so easily distinguished. Fish that make a series of short visits to a partner, or display-eliciting situation, seldom face and turn broadside more than once per visit.

c

Fig. 2. Lateral views of facing (a) and broadside (b, c and d) fish. The broadside fish are displaying to their mirror images, which are on their far sides. Note that while the the nearside pelvic fin (i.e. the side near to the 'partner') is erect, the one on the offside may be more or less with­ drawn. (In pelvic fin flickering, it is the offside pelvic fin that is flickered to and fro). •=The second of the two fish that are the subjects of Figs l, 2 and 3.

When carousel/ing, the fish are parallel to each other, but one's head is opposite the other's tail. The pair may hold this mutual orientation for as long as 15 sec, and the two fish may circle slowly. Sometimes one of the fish flashes its tail (p. 16), especially when the other moves its head slightly closer.

In lateral display the fish are also parallel, head to head. They may stand still and beat their pectoral fins rapidly, and they may beat their tails at each other (Lissmann, 1933 and Laudien, 1965). They may also swim along together, now one ahead, now the other, and they often beat their tails as they do so. Braddock (1955) has called this 'jockeying for position'. Mouth locking occurs sometimes after the fish have begun to bite each other, when one takes hold of the other's upper or lower lip, and then they may spend as long as 1 min pulling and tugging, often lying on the substrate as they do so, and in some risk of drowning (Lissmann, 1933 and Smith, 1937). Postures and patterns. Fins spread. As a fish turns towards a display-eliciting stimulus for the first time, the vertical fins are spread (and the gill covers are erected at the same time if the stimulus appears close, or a second or so after­ wards if it is not so close). Figure 1 shows the contrast between a displaying and a non­ displaying fish. The dorsal is the last fin to be erected fully, probably because that is the fin that has to be lifted furthest against gravity. The criterion for fins spread is thus an erect dorsal. However, when a displaying fish approaches another one, the first few dorsal rays may be slightly lowered, but the remaining ones remain rigidly erect. Humped body. During an approach there may be a slight increase in the curvature of the line of the fish's back, especially between the snout and the dorsal fin. (Lissman, 1933 described this posture.) Head down posture. This may be accentuated by humping. The whole body axis is inclined slightly downwards. Approaching fish, females in the first stages of courtship and fish beating their tails (Fig. 3) show this posture. Head up posture. The whole body axis points upwards, and females that have been chased a few times, and males displaying to females under their nests sometimes show this. But such a female is probably hiding just beneath the surface, so that the head-up posture merely

UNITS OF BEHAVIOUR IN THREAT DISPLAY

facilitates air gulping with minimum move­ ment, and in the male the posture may be a consequence of nest building. However, the slightly head.up posture of some fish when both pelvic fins are held erect in broadside fish is not so easy to explain (Fig. 2). Tinbergen (1951) describing stickleback behaviour, and Forselius (1957) describing anabantid behaviour suggest that head-up signals fear, and head-down signals attack. Colours and patterns. The patterns described here are easily recognized, and transitions from one to the other are often quick and sharp, i.e. 2 or 3 sec, but sometimes intermediates may be held for minutes on end. Unfortunately the domesticated males do not show the subtle changes and intermediates that can be seen in the wild-type fish and in some domesticated females. In the wild-type fish, colour and pattern are changing moment by moment, and could be very sensitive indicators of the fishes' internal states. (Of course, some of the changes, such as those when the wild fish come up to the surface for air, may merely have concealing functions.) Lissmann (1933), Braddock & Braddock (1955), Forselius (1957) and Kiihme (1961) have described Betta's colour and tone changes. Forselius (1957) also describes those of other anabantid fish, and Barlow's (1963) description of those of Badis badis shows how to look for subtle changes in pattern.

In the threat display of both wild males and females, and in courtship in the males, the body and especially the head darken until the body is a velvety red-black, and the head and dorsal parts of the body are nearly jet black. The reds, greens and blues in the fins and parts of the 'irises' of the eyes become more deeply satur­ ated, and are accentuated by contrast with the darkening body. The gold and red on the distal parts of the opercula are also accentuated. Some domesticated males show all these changes, but many of the lighter coloured males (e.g. the pink, grey-blue, and lavender fish) do not be­ come blacker when they display.

15

In the early stages of courtship, five to seven dull gold vertical stripes appear on the females' flanks. Mature females will already have a gold patch on their bellies, and hints of vertical stripes near these patches. During the early stages of courtship, females' fins do not necessarily show an increase in the saturation of their colours, and towards the end of their courtship both the males and females are duller than they were in the first 5 or 10 min. Fish that have been frightened (e.g. by a blow on the walls of their tank) go paler in tone, some­ times to a dull straw colour, and they show black longitudinal stripes. The top stripe runs through the eye, and the lower one starts on the cheek. Both extend to the base of the tail. These stripes are sometimes visible even in fairly dark­ toned fish. Sometimes, especially at the begin­ ning of courtship in females, they are overlaid by vertical stripes, to give a plaid effect (Brad­ dock & Braddock 1955). Wild fish that are not displaying, and have no territories of their own, are usually a dull olive colour, with rather pale fins, and the longi­ tudinal stripes just visible. Thus the darkening, and the saturation of their reds and greens is all the more striking when they display. In a tank with fish that hold territories, single males without territories often have dark fins and a uniformly pale body. Pale-toned fish sometimes show a black spot at the base of the tail, and such spots are prominent in young and in wild fish. Movements of parts of the fish relative to the whole. Gill cover erection (Figs ld, 2 and 3) is a sudden increase in the distance between the distal edge of the operculum and the body, regardless of how far erect the operculum was to start with. The end of a gill raising bout is marked by a sudden decrease in this distance, even if the opercula are not completely closed thereby. In practice such changes are clear-cut, although different individuals have different degrees of opening for what are here recognized as 'open' and 'closed' positions. When the gill covers are erected the brachiostegal membranes

16

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

are usually protruded. Different degrees of pro­ trusion were not distinguished. Gill cover erec­ tion often accompanies the act of turning to face. It has been mentioned in most descriptions of threat and courtship displays (Kiemendeckel­ abspriezen in German). Braddock & Braddock (1955) refer to the combined erection of the gill covers and turning to face the partner as a 'challenge', ·and they also distinguish in­ dividual from mutual challenges, when both partners raise their gill covers simultaneously. Laudien (1965) and Clayton & Hinde (in press) use frequencies of gill cover erection in measur­ ing threat displays, while Lissmann (1933), Hess (1952) and Marrone (personal communication) have used duration measures, as is done here (chapters 6 and 7). Bites and nips are given by facing fish, and bites are likely once a fish starts to lower its gill covers as it turns to face. A bite is a sharp opening and closing of the fish's mouth, and it has been distinguished from a biting attempt Braddock & Braddock (1955) where the mouth is held open for at least ! sec, and where the open mouth is not always directed at the partner. Biting attempts, perhaps better termed biting threats, are likely early in display, especially when the fish is facing the front end of its partner. Then the facing fish opens its mouth near the operculum of its partner about 1 sec at a time. If the partner whips round so that the two are in head-to-tail positions, then each fish may direct a bite to its partner's tail, and usually they both miss because they are beating their tails and moving forward at the same moment. (In the longer finned domesticated males, which are less able to evade each other quickly, bites are more likely to cause tears in the fins, Nips usually accompany brief accelerations towards the anal and caudal fins of a retreating fish, but they seldom touch that fish. Courting males may charge and violently ram females, but I have never been able to see whether their mouths were opened when they did so. Pectoral fin beating often changes frequency (Lissmann, 1933; Braddock & Braddock, 1955;

and Laudien, 1965). Such changes occur when a strange object is placed near the fish, or when its displaying partner edges nearer. Note that in the drawings in Figs 1, 2, and 3 only la, b and c show the positions of the pectoral fins. Because these fins are transparent, they did not show well in the photographs from which the drawings were made. Pelvic fin flickering, tail beating and tail flashing are given almost exclusively from the broadside position. In pelvic fin flickering, the pelvic fin on the side opposite to the partner is moved to and fro through an arc in the vertical plane. The angle subtended by this arc may be as small as 20°, or as large as 100°. In each bout of fin flickering there are usually at least three flickers. Bouts are easy to distinguish, because interbout intervals last much longer than the

a2

c2 Fig. 3. Fish beating their tails at their mirror images in al, a2, cl and c2, and at a stationary puppet held outside the tank in b.al and a2, and cl and c2 are from successive frames of a 16-frame per sec cine film. In a2 and c2, the cupped tail drives water slightly forward towards the mirror image which is lying parallel with the fish, while in b the tail is aimed backward towards the puppet. Note the positions of the pelvic fins mentioned on p. 13.

UNITS OF BEHAVIOUR IN THREAT DISPLAY

flickers, which take from t to -k sec each. This study uses measures of numbers of bouts of pelvic fin flickering. In wild-type fish, and in some domesticated ones, the movement is conspicuous because the pelvic fins are tipped with white. It is referred to as Pendeln in Kiihme's (1963) study of courtship, and in Laudien's (1965) study of the threat display. Tail beating is recognized by the suddenness and speed of the movement, which seldom takes more than t sec; by its amplitude which exceeds that usual for a fish that is accelerating away from something; and by the fact that the tail is cupped in the direction of the partner (Fig. 3). Tail beating has been described in cichlid fish by Baerends (1950) and Tinbergen (1951), and in Betta by Lissmann (1933) and Forselius (1957). The preceding criteria distinguish tail beating

17

from the sinuous movements called undulations by Thompson & Sturm (1965 a and b). Tail flashing is a sudden fan-like closing and opening of the caudal fin rays. In wild fish this movement is very conspicuous because it momentarily hides the bright green streaks be­ tween the crimson-maroon fin rays. In domesti­ cated Bettas without these markings, the suddenness of the movement nevertheless makes it conspicuous. It often occurs just as the fish turns to face, and sometimes just afterwards. In films of displaying and fighting cichlid fish one can sometimes see a similar momentary decrease in the area presented by the caudal fin. Baerends, Brouwer & Waterbolk (1955) describe tail fluttering in cichlids, defined by the lifting of the most dorsal fin rays of the caudal fin, thus momentarily increasing its area.

4. SEQUENCES AND RELATIVE FREQUENCIES OF MOVEMENTS IN ONE FISH'S DISPLAY The units common to the threat and courtship displays of all :fighting fish were described in the previous chapter. These units recur many times in the displays of both participants in any encounter. Yet it has been suggested that the outcome of an encounter may be related to the differences between the displays of the two participants. If both use the same movements, then any differences between their displays must lie in the relative frequencies, sequences and timing of the component movements. Such differences could be differences in the patterns of the individual's displays, and they could also be consequences of the ways in which different individuals responded to their partner's displays. This chapter starts with the displays of in­ dividual fish, regardless of how their displays were elicited. Fortunately some individual fight­ ing fish will display to stationary puppets, when all pattern in the display must be generated by the displaying fish alone. A description of such a display may guide subsequent analyses of inter­ actions involving pairs of fish. If, for example, fin flickering always occurs in a fish 1 sec after it has turned broadside, then to know the effects of the partner's display on fin flickering is also to know the effects of its display on turning broadside. This chapter describes methods for finding pattern in the display, and for testing whether this pattern could have occurred by chance. The display is very well suited to analyses of pattern because the orientations facing and broadside alternate-the act of turning broad­ side ending the facing bouts, and the act of turning to face ending the broadside bouts. Moreover, pelvic fin flickering, tail beating and tail flashing usually occur only while the fish is broadside. Thus the display could be described in terms of the frequency with which the fish goes through the facing-broadside cycle, and the frequency per cycle of the broadside move­

ments-pelvic fin flickering, tail beating and tail flashing. However, the proportion of time a fish spends facing (and with its gill covers erect) also varies from fish to fish, and from time to time in the same fish, and is related to the outcome of an encounter between two strange fish (chapter 6). How can such duration measures be combined with the above mentioned fre­ quency measures in a description tha tis not too cumbersome to interpret? Hinde (1958) and Cane (1961) discuss the difficulties ofinterpreting frequency and duration measures, and explain that one difficulty follows from the fact that they tell nothing about the distribution of bouts of different lengths. For some purposes, especially when a single activity, such as mistle thrush singing (Isaac & Marler, 1963), is being analysed, a histogram is adequate for describing the num­ bers of bouts of particular lengths. Obviously the bouts of facing and broadside (or with the gill covers erect and lowered) could be described thus. But how could the information contained in the histogram (say of the broadside bouts in a 15-min sequence of display) be combined with the frequency information about pelvic fin flickering etc.? It is attempted here to solve this problem by using the information about the distribution of (say) broadside bouts of different lengths to describe the broadside behaviour in terms of the frequency with which the fish turns to face (this is the act that ends a broadside bout) in successive intervals (lt sec long) after the beginning of the broadside bout. In addition to the frequency of the event which ends the broadside bouts, data of the frequency of other events, such as fin flickering, in the success­ ive intervals after the fish turned broadside, can be included in the description. Nelson's (1964) method for describing the temporal patterning of courtship display in glandulocaudine fishes suggested to me the method of analysis described in this chapter. 18

SEQUENCES AND RELATIVE FREQUENCIES OF MOVEMENTS

The aim of this method is to provide a crude measure of the frequency with which an animal performs some action at different times after some reference event. For example, it is possible to describe the broadside behaviour of a par­ ticular fighting fish in terms of the rates of fin flickering and turning to face (the act which ends a broadside bout) at different times after the broadside bout began. In 4 min of display, one fish turned broadside 52 times. It is immediately obvious from the raw polygraph record that different broadside bouts are of different lengths, so that while the fish may be beating its tail in the 4th sec of some of the bouts, it may already have turned to face before others have lasted 4 sec. How are we to compare these different bouts for tail beating behaviour, say, at different times after their beginnings ? One method is to correct the number of re­ sponses given at different times after the fish turned broadside to 'rate of responding per opportunity to respond'. This term comes

from the work of Anger (1965) and Blough (1958), and their methods parallel mine. Kelleher et al. (1959), describing inter-response times of pigeons working on certain reinforcement schedules also use this method of analysis. To give an example from Betta's display: after the above mentioned fish had turned broadside, it turned to face 12, 13, 13, 6, 6, 1 and 0 times during the 7 successive sec since the broadside bout began, and once more later than 7 sec after the bout began. It is difficult to compare the figures in the successive seconds directly in this histogram, for while the fish has just turned broadside on 52 occasions at tO, at the beginning of the 2nd sec it is still broadside on fewer occasions, i.e. 52-12, or 40. In other words, while there are 52 'opportunities to respond' at tO, there are only 40 opportunities at tO + 1. To compare the broadside behaviour in the successive seconds after the fish turned broadside it is necessary to correct the opportunities to respond to the

0-80 ~ 0 u

~

0-60

0-40

0.20 0.10

2

19

3

4

5

Seconds since turning broadside Fig. 4. Broadside display of one fish in the presence of a stationary puppet. P-pelvic fin flickering TB-tail beating TF -tail flashing F -turning to face

20

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

same figure in each of them. To do this, the histogram is first expressed as a survivorship curve: 52, 40, 27, 14, 8, 2, 1. This shows how many opportunities to re­ spond there are at the beginning of each second. Given the actual numbers of responses during the successive seconds, as shown above, the responses can be corrected to 'response rates per opportunity to respond': 12/52 or 0·23, 13/40 or 0·33, 0·48 etc. as shown in Fig. 4, for the rate of turning to face per opportunity to do so, in successive seconds after the fish turned broad­ side. The rate of tail beating in successive seconds of the broadside bout can be expressed in the same way: 8/52, 12/40 etc., or 0·15, 0·13 etc. Of course, it is possible for actions performed while the fish is broadside to have rates of response per oppor­ tunity to respond greater than 1·0. This is not possible for the act of turning to face, because this ends the broadside bout, by definition. Such an analysis may also be applied to the occasions when the reference event is a change in the behaviour of another fish. To express the rate of tail beating in successive seconds after the partner turned to face, the number of tail beats in each of the successive seconds while the partner is still facing is divided by the number of times the partner turned to face. To discover the rates in the successive seconds while the partner is still facing it is necessary to divide the tail beats in each second by the number of times the partner faces for as long as the cor­ responding second. The picture of the behaviour patterns which such a method provides is crude and limited in many ways. Moreover, it may have arisen by chance. After discussing some of the method's limitations, statistical tests that can be applied to the pattern are described. Figure 4 shows how the rate of ending the broadside bouts by turning to face gradually increases as the bouts get longer. Such changes are revealed only when a population of broad­ side bouts is studied. Thus it is always an in­

ductive step to say that such a curve refers to changes occurring during the performance of any one broadside bout, which make it pro­ gressively more likely to end. Such changes can be either inside or outside the fish, or both. An example of an external change that could produce such a pattern would be for the fish's partner to turn and flee whenever the fish stays broadside more than 2 sec, whereupon the fish would follow its departing partner and so end its broadside bouts at about that time. Figure 4 contains all the information about the rates of the movements shown per second, for the successive seconds after the fish turned broadside, at a resolution in time of 1 sec. Because the figure is based on a population of broadside bouts, it contains no information about how the different actions done while the fish is broadside share individual broadside bouts. While the figure suggests that tail beating usually follows pelvic fin flickering, this need not be the case if pelvic fin flickerings hardly ever share the same broadside bout, and occur in the reverse order on the few occasions that they do share a broadside bout. Thus, strictly speaking, conclusions drawn from an analysis such as the foregoing should be restricted to conclusions about the occurrence of the display components with respect to the reference event-turning broadside-and not with reference to each other. Interpretations about how the other movements occur with respect to each other should be made only when it is known that the components share individual broadside bouts in the way that would be expected from the way in which they share the successive seconds of the whole population of the broadside bouts. Such a representation of the behaviour as that in Fig. 4 refers to the 52 bouts which occurred in the finite time of 4 min. Such a method cannot show whether changes in the pattern of broad­ side behaviour occur over short times, for the fewer the broadside bouts that contribute to the analysis, the more likely is chance to play the major part in determining the pattern re­ vealed by the analysis.

SEQUENCES AND RELATIVE FREQUENCIES OF MOVEMENTS

This way of describing behaviour is also limited because the time intervals into which the broadside bouts are divided are of finite lengths, such as 1·0, or more usually 1·5 or 3·0 sec. So a frequency of tail beating of, say, 0·15 tail beats per opportunity to do so in the first 1-sec interval after the fish turns broadside does not equal 'frequency of tail beating per second spent broadside'. The actual frequency lies between 8/52 (its value if all the broadside bouts begin­ ning at tO last for the whole of the succeeding second), and 8/40 (its value if the 12 bouts which end during the 1st sec do so the instant after tO.) Of course, actual frequencies can always be obtained by measuring individually the durations of those bouts which end in the first second, and then adding this total to the 40 sec of broadside contributed by the remaining 40 bouts, which survive beyond the 1st second. In summary, this method yields generaliz­ ations about finite populations of bouts of be­ haviour, described at a finite resolution in time. From these features follow its limitations. All the patterns found by this method should, ideally, be tested against the hypothesis that they have arisen by chance. The simplest tests are those for the repeat­ ability of the pattern, from population to population of bouts. For example, in Fig. 9 (p.32) uses data about the frequencies with which different subjects flicker their pelvic fins in successive intervals after their partners have raised their gill covers. All the fish flickered their pelvic fins more often in the first interval than they did in the second one. In such a case a sign test can be used, but tests for analyses of variance can be used to test for the variation in frequency over more than two successive in­ tervals (e.g. Friedman's two-way analysis of variance, described by Siegel, 1956). If, however, the data come from a single population of bouts, as in the example worked out above, then a test which shows whether the pattern, such as the distribution of fin flickering in the broadside bouts, could have arisen by chance in the population can be used. Since the

21

values of response per opportunity to respond are based on a distribution of responses after some reference event, the distribution of the event into the successive intervals can be com­ pared with that which would be expected by chance. Since fewer than five events occur in some of the intervals, and since it is best not to lose information about the distribution of the behaviour in time by combining adjacent cate­ gories, the Kolmogorov-Smirnov one-sample test is to be preferred to the chi-squared one-sample test (Siegel, 1956). (To compare the distributions of responses in two populations, or that of the same fish's responses on two occasions, the corresponding two-sample tests can be used.) To illustrate the use of the Kolmogorov­ Smirnov one-sample test, the case of a single fish, beating its tail in successive 1·5-sec intervals after it had lowered its gill covers will be used. (Gill cover lowering often coincides with turning broadside.) The distribution of tail beats into the successive intervals was: 31, 17, 8, 5, 7, 2, 3, 5, 3. At the beginning of each of the successive 1·5-sec intervals after the partner had lowered its gill covers, the 'opportunities to respond' (i.e. the numbers of occasions on which the fish still has its gill covers down at the beginnings of the successive intervals) were: 29, 26, 18, 13, 11, 9, 6, 6, 5. The number of tail beats expected to fall into each of the successive intervals, can now be calculated, given that there is a total of 81 tail beats and 123 opportunities to respond. From these figures the mean rate of tail beating per opportunity to do so is 81/123. Given the actual numbers of opportunities to respond in the successive intervals, the numbers of tail beats expected to fall into each of the intervals can be calculated. For the first interval the expected value is 81/123 x 29, or 19· 1. The expected values in all the intervals are: 19·1, 17·2, 11·9, 8·6, 7·9, 7·5 etc. The Kolmogorov-Smirnov test compares cum­ ulative distributions: Observed: 81, 50, 33, 25, 20 etc., and Expected: 81, 61 ·9, 44·7, 32·8, 24·2 etc.

22

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

This test focuses on the maximum deviation, which is 61 ·9-50, or 11 ·9 (in the second interval). For an N of 81, this deviation is significant at the 0·05 level of confidence (two-tailed test). In other words, the fish is not equally likely to beat its tail in all the successive 1·5 sec intervals after it has lowered its gill covers. Temporal pattern in the display, regardless of the display-eliciting situation. The previous chap­ ter showed how the facing and broadside orien­ tations are mutually exclusive, and Fig. 4 in this chapter suggests that during a broadside bout pelvic fin flickering was the most likely movement early in the bout, tail beating in the middle, and tail flashing at the end. The follow­ ing generalizations about the display's temporal pattern are based on analyses similar to the pre­ ceding one, using raw data from the experi­ ments described in chapters 6 and 7. 1. Facing and broadside orientations alternate, sometimes as often as ten times per minute, usually six to twelve times per minute (Table I). In some fish this alternation continues even in the presence of a stationary puppet, and in most fish in the presence of their mirror images, which 'respond' in an unusual way compared with 'real' partners, where the partner faces in turn, not simultaneously. 2. The frequency of pelvic fin flickering per 1·5- or 3·0-sec interval is usually greatest in the first interval. (This was so in 5/6* fish displaying to a stationary model, from the experiment described in chapter 7, and in 14/15 of the females displaying with complete access to each •Tue six fish that spent most time near the puppet were used in this analysis.

other, from the experiment described in chapter 6.) 3. Pelvic fin flickering was more frequent than tail beating and tail flashing in the first interval in the broadside bout in 6/6 fish with the station­ ary model. In this respect, fish displaying with each other are less uniform. Several of the females described in chapter 6 beat their tails more frequently than they flickered their pelvic fins in the first interval. 4. Tail flashing was never most frequent in the first interval after the fish had turned broad­ side. Often tail flashing was the last act of the fish before it turned to face. Such generalizations about the display, as 'pelvic fin flickering usually precedes tail beating, and tail flashing is usually the last movement in a broadside bout' reflect redundancies in the display. But if the display is relevant to the outcome of an encounter between the two fish, the display may be communicating something about at least one of the fish, so that one finally stops before the other. Of course it is also possible that the two fish give identical displays, but that they differ in responsiveness to the display of their partners, and it is even possible that the fish that gives up first is merely the one that gets tired first. (For this possibility see chapter 6.) Assuming that the display com­ municates that which makes the subjects differ­ ent from each other, so that there is some final result of their interaction, such differences in the display have yet to be found. Such differences could obviously lie in the relative frequencies of the movements given while the fish is broadside, and this possibility is considered in chapter 7.

5. SECOND BY SECOND INTERACTION OF TWO DISPLAYING FISH The occurrence of a particular display move­ ment in one fish may affect the behaviour of its partner in the next second, and it may also have longer term effects, possibly relevant to the final outcome of the encounter. This chapter considers the short-term effects of display move­ ments only, and their possible long-term effects are discussed in chapters 8 and 9. After watching any displaying pair of fighting fish for a minute, the observer will be convinced that the display is unlikely, on closer analysis, to prove to be a chain response, with each move in one of the fish leading to a particular move in its partner, which evokes the next move in the first fish. In other words, the type of diagram by which Tinbergen (1951) describes the inter­ action of two courting three-spined sticklebacks (Gasterosteus aculeatus) is unlikely to apply to Betta splendens threat display. In fact, most interactions fail to reveal such simple patterns. Examples of descriptions that hint at the com­ plexity of the interactions considered are the analyses of Morris (1958) of the courtship of the ten-spined stickleback (Pygosteus pungitus) and Hinde's (1955/6) analyses of the courtship of various finches. Of course there are examples of interactions that can be described as the sum of one partner's responses to the other's actions. Any one of the responses of a turkey hen to her mounting mate may be elicited alone by suitable manually provided stimuli (Schein & Hale, 1965). It is possible to make precise descriptions of interactions of the usual type where the actions of one animal are not always followed in a rigid one-to-one manner by particular corresponding actions in the other. Dane & Van der Kloot (1964) describe the interactions of golden-eye ducks (Bucephala clangula) thus, and Altman (1967) describes this method for rhesus monkey interactions. For an action A in one animal, its temporal relation to actions A, B, C etc. in the partner must be considered in turn. How many times for example, does B in the partner

follow A in the first animal, out of all the occa­ sions when B could follow? The number of times that B might be expected to follow A in the first animal by chance can be calculated from the proportion of B in the partner's total behaviour during the time when the two were interacting. Then the value expected by chance can be com­ pared with that found, and a significant differ­ ence between the found and expected values suggests a causal relationship between As in the first animal, and Bs in the second. The relation need not necessarily be a simple and direct one. The frequency of Bs following A in the first animal may change, and the significance of a change in responsiveness of Bs by the second animal to the first can be measured statistically. This chapter describes an approach which is similar to the preceding in principle, with the refinement that it is specified whether the Bs fall into the first, second, third etc. of a series of defined intervals after the occurrence of the first animal's As. In describing the effect of the fish raising its gill covers in the subsequent tail beating in its partner, the tail beating in the first, second, third etc. of a series of l ·5-sec intervals after the fish raised its gill covers is expressed as a rate of tail beating per oppor­ tunity to do so, by the method described on p. 19. Here, the analyses of facing and broadside behaviour are based on the behaviour of pairs of fishes separated from each other by Perspex screens. Pairs of adult male domesticated fish were exposed to each other for the first time, and allowed to display for an hour. The fishes referred to as Fish 1 and Fish 2 were watched in two sessions separated by 24 hr. They were not allowed to see each other between the sessions. Figures 7 and 8 show how consistent each fish was in his facing and turning broadside be­ haviour over the 2 days. In the recording for these observations, the facing and broadside behaviour of one of the fish were recorded with the keys pressed by fifth and third fingers respectively of the left hand, 23

24

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

and the corresponding orientations of the other fish were recorded by the fourth finger of the left hand and the third finger of the right hand. The analyses of tail beating and gill raising behaviour are based on records of the inter­ action of adult female domesticated Bettas whch had complete access to each other. (Detailsi of recording methods appear in chapters 2 and 6). The frequency of occurrence of an action is obtained by dividing the number of times that action occurred by the number of intervals in which it could have occurred. (See also Chapter 4.) It is expressed in terms of the frequency of occurrence per opportunity to occur. For ex­ ample, in Fish 1 in Table Illa, there are 90 occasions when it is facing and its partner turns to face it. By the end of the succeeding 1·5-sec interval, Fish 1 had turned broadside on 72 of the occasions, making its frequency of turning broadside per opportunity to do so 72/90, or 0·80. The time intervals were usually 1·5 seconds long, and they are always of the same length in any one analysis. The time since the reference event-the moment when the partner turned to face Fish 1 when it was already facing-is expressed in the number of intervals since that reference event. Analysis of the interaction of facing and broadside fish is simplified because a facing fish can only stay facing or tum broadside, and a broadside fish can only tum to face, or stay broadside. The first analyses are restricted to the ways in which the cycles-facing orientation, turning broadside, broadside orientation, turn­ ing to face-interlink in two displaying partners. Later analyses describe the places of pelvic fin flickering and discuss their involvement in the coordination of these cycles. In the domesti­ cated females, on which these analyses are made, it is assumed that gill cover erection concides with the act of turning to face, and that gill cover lowering coincides with turning broadside. The Data Many threatening pairs of animals move to and fro as they fight and display. Tinbergen

(1952) describes how a pair of male sticklebacks is now in the territory on one of them, now in the other's. At one moment one seems to be chasing and the other to be fleeing, and at the next they have reversed these roles. It is tempting to compare the facing orientation of Betta with chasing, and the broadside one with fleeing, especially when a displaying pair of territory­ owning fish stays close to their mutual boundary. This analogy between fighting fish facing and turning broadside, and sticklebacks chasing and fleeing is further supported by the finding that a facing fish's partner is usually broadside, and the fish spend very little of their time mutually facing. When two adult male domesticated fighting fish are separated from each other by a Perspex screen, they may face each other strictly in tum over a run of as many as 12 facing-broadside cycles. Such results could be achieved if the facing broadside cycles of all fighting fish had similar periods. However, if different pairs of fish in this situation are watched over 5-min periods, the similarities between the facing rates of the members within the pairs are greater than the similarities between pairs, as Table I shows. Table I. The Number of Times in the first 15 min ot Interaction that Each of Seven Pairs of Fish Turned to Face its Partner The fish were separated from each other by Perspex screens FishA FishB 65

65

52

54

30

35

31

28

29

27

30

26

14 18 In each pair, the individuals were randomly assigned to the Fish A and Fish B columns.

In other words, the facing rates of fish separated by Perspex screens are correlated (rS = + 0·84, P = 0·05 to 0·02, two-tailed test).

INTERACTION OF TWO DISPLAYING FISH

What hypotheses about the displays' co­ ordination can we suggest at this stage? The clock in one church tower may always strike a fow seconds after that in a neighbouring church. Yet, so long as no one adjusts the two clocks, they could be said to be behaving independently, except in so far as both are subject to the same gravitational field. And a single Betta can display to a stationary model at rather a constant rate­ 29, 19, 20, 19 and 16 times over five consecutive 5-min periods with the model. But, when fish display at each other, the variation from pair to pair exceeds that within the pairs, as Table I showed. The two-clock model is an extreme version of an hypothesis of behaviour unfolding inde­ pendently of environmental changes. An equally extreme alternative hypothesis is a 'chain reflex' one, where an action in one of the fish is a necessary and sufficient condition for a particular action in the other. In such a strong form, how­ ever, this hypothesis is untenable, as the data in chapter 4 about the display occurring in the presence of a stationary puppet show. Although each fish can produce the whole display pattern independently of moment to moment stimulation from the environment, or in the presence of unusual stimulation such as that from its mirror image, it remains possible that displaying fighting fish behave in a 'chain reflex' manner when they are displaying with another real fish. Individuals of pairs of certain 'duetting' shrikes (of the genus Laniarius) can produce the whole 'duet' on their own, but they can also give their part of it in precisely timed response to their partner's part (Thorpe & North, 1965). For the fighting fish interaction, is it possible to postulate the details of a chain, assuming that its links are the acts of turning to face and turning broadside? For example, the facing­ broadside cycles of the two fish may be 180° out of phase, with one of the fish always leading, as in Fig. 5a. Assuming that the temporal relations between the individuals' displays are consequences of

25

time ~

a.

b.

c.

Fig. 5. Possible sequences of turning broadside and turning to face in pairs of displaying fish. - - - facing - - - - broadside

stimulus-response relations, the second fish is responding to turning to face in its partner by turning broadside, and to turning broadside by turning to face. In Fig. Sb, each fish could be affecting the other, but the stimulus response relation would be asymmetrical. The second fish follows the first's turning to face and turning broadside with the same movements, while the first follows the second with the opposite movements. Neither of the preceding patterns is often seen in the raw polygraph records. Figure 5c shows a more common pattern. If the behaviour of each fish is regarded as an alternation of facing and not-facing orientations, then each fish turns to face after a few seconds without there having been any immediately preceding change in the partner's behaviour, but neither fish stops facing until its partner has turned to face it. Thus, like most other complex behaviour patterns with complex 'inputs', such as a locust's flight (Weis-Fogh, 1964) some parts of the pattern are affected more than the others by the input, and no part of the output necessarily bears a one-to-one relationship with the input. (See also Weis-Fogh, 1964.) Figure 5c suggests that, if each fish responds at once to the act of turning to face in its partner by turning broadside, the two would face an equal number of times over any finite period of time, and they would con­ sistently take it in turns to do so.

26

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

In terms of the parallels between the fighting sticklebacks and the displaying fighting fish, each fish only stops chasing (facing in the fighting fish) when its partner turns round to chase it back. If facing, in Betta, symbolized chasing, then it is possible that displaying Bettas com­ municate their readiness to attack by how soon they turn to face again after they have turned broadside. Ethologists have often described displays as if the displays indicated the animals' readiness to flee (see discussion in chapter 9) as well as to attack, and a fighting fish's readi­ ness to flee could be communicated by the pattern of behaviour (pelvic fin flickering, tail beating, etc.) while the fish is broadside. Whether such an approach to the display is fruitful will become clear after the interaction of facing and turning broadside has been analysed more rigidly. It will also become clear that the descrip­ tion of the display in Fig. Sc is over-simplified. Analyses of the Second by Second Interaction Turning to face and turning broadside. The facing-broadside cycle of one fish does not always seem to be closely linked to that of its partner. Although two fish may face each other in turn over six or ten cycles, the moment when one fish turns to face relative to the other's cycle is seldom the same cycle to cycle. If the fish are separated by a transparent screen, one usually faces the other while it is still facing, but it may do so sooner or later, and quite often a fish does not face its partner until the partner has turned broadside of its own accord. A simple hypothesis about the interaction is that the chance of a fish turning to face, or turning broadside, depends on the partner's orien­ tation, and neither turning to face nor turning broadside is triggered by particular events in the partner's behaviour. For example, the frequency with which a facing fish turns broadside may be greater when the partner is facing than when it is broadside, but no greater in the 1st sec after the partner has turned to face than in the 3rd sec. Table lib compares the frequency of turning to face in four different facing fish in the presence

of partners that have either been facing or broadside since the fish turned broadside. The table focuses on the occasions when the fish turned broadside in the presence of a partner which was already facing or broadside, and which held its orientation until the fish turned to face again. The table refers to the frequency of turn­ ing to face in the fish in all the intervals of its broadside bout. In only one of the fish does the Table II. Frequency per 1 ·5 sec Interval of Turning Broad­ side by a Facing Fish (Ila), and of Turning to Face by a Broadside Fish (Ilb) in the Presence of a Partner that Remains Facing or Broadside Ila Turning broadside in the presence of a part­ ner that is Fish facing broadside 0·67 (46/69)

0·39 (68/176)***

2

1 ·00 (10/10)

0·14 (19/136)

3

0·71 (88/124)

0·36 (13/33)*

4

0·69 (30/44)

0·60 (3/5)

Ilb Fish

Turning to face in the presence of a partner that is facing broadside 0·26 (27/103)

0·23 (40/174)

2

0·48 (48/101)

0·38 (34/59)

3

0·50 (148/294)

0·65 (33/51)

4

0·31 (74/239)

0·78 (14/18)••

•=difference in distribution of acts of turning broadside (or turning to face) between occasions when partner facing and broadside significant by x-squared one­ sample test, at 5 per cent level. (* • for 2 per cent level, and • ** for 1 per cent level.)

partner's orientation make a significant differ­ ence to the frequency with which the fish turns to face, although, as might be expected from the discussion on p. 25, three of the fish are more ready to face a broadside than a facing partner. Table Ila makes a similar comparison for fish that have turned to face partners that re­ main facing or broadside all the while. All the fish are more likely to turn broadside with a facing than a broadside partner. Tables Illa and lllb focus on the I ·5 sec interval after the partner has changed his orien­ tation, regardless of when it did so relative to the

INTERACTION OF TWO DISPLAYING FISH

fish's facing broadside cycle, except that in Table IIIb, referring to the fish's turning to face, the fish must have been broadside already when the partner changed his orientation, and for Table Illa referring to the fish's turning broad­ side, the fish must have been facing when the partner changed his orientation. Table ill. Frequency of Turning Broadside by a Facing Fish in the First 1 ·5-sec interval after the Partner Faces and Turns Broadside (lla), and Frequency or Turning to Face after the Partner Faces and Turns Broadside (llb) Illa Fish

Turning broadside after partner faces turns broadside 0·80 (72/90)

0·15 (17/114)"'

2

0·59 (51/86)

0·19 (20/108)"'

3

0·51 (105/208)

0·16 (48/296)"'

4

0·29 (93/247)

0·15 (39/251)*

Turning to face after partner

Illb Fish

27

faced it, and turned broadside to it. Thus a fish may seem more ready to turn broadside after being faced by its partner than after the partner turns broadside to it, because the partner faces at a time when the fish is more likely to turn broadside anyway. Table IV controls against this possibility, by specifying the stage during the fish's facing bouts at which the partner turns to face it, or turns broadside to it. Table IV. Frequency of Turning Broadside by a Facing Fish

in the First 1 ·5-sec Interval after its Partner Turns to Face or Turns Broadside, when the Intervals in the Fish's Facing

Bout, in which the Partner Changes Orientation are Matched Interval in which partner faces or turns broadside

Partner faces

First

0·69

Second

1·00

Remainder

1·00

faces

turns broadside

0·09 (10/113)

0·44 (53/120)"'

2

0·24 (30/124)

0·28 (38/138)

First

0·33

3

0·56 (39/70)

0·55 (45/82)

Second

0·86

4

0· 19 (13/70)

0·34 (17/50)

Third

1·00

Remainder

0·69

First

0·46

Second

0·31

Third

0·22

Remainder

0·33

First

0·20

Second

0·27

Third

0·43

Remainder

0·48

"'=difference in distribution of acts of turning broadside or turning to face between intervals after partner turns to face, or turns broadside, significant by x-squared one-sample test at 0· 1 per cent level.

Table Illa shows that after being faced a facing fish is more likely to turn broadside than after its partner turns broadside to it. Table IIIb shows that turning to face in the fish is less affected by whether the partner has just turned to face, or has turned broadside; but, as might be expected, a broadside fish is more likely to turn to face if its partner has just turned broad­ side to it, than if its partner has just turned to face it. Table III is based on data about all the occa­ sions when the fish changed orientation in the first l ·5-sec interval after the partner had turned to face, or turned broadside. It is therefore possible that the results reflect the times during the fish's facing-broadside cycle when the partner

Partner turns broadside Fish 1

0·34

0·50 Fish2

0·16

0·33 Fish 3

0·24 0·32

0·19 Fish4

0·12 0·12

0·18

Because the partner turns broadside in fewer of the fish's facing bouts than those in which it turns to face earlier intervals must lumped into the 'remainder' category in the 'Partner turns broadside' column. Thus for Fish 1, 0·50 is the frequency with which Fish 1 turn's broadside in the next interval after the partner turned broadside, on all those occasions when the partner turned broadside to the fish after the first interval after the fish turned to face.

28

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BEITA SPLENDENS

At whatever time after the partner faces or turns broadside to the fish after it turned to face, the fish is more likely to tum broadside after the partner turned to face than after the partner turned broadside. In summary of the analysis so far, facing fish tum broadside more frequently with facing partners than they do with broadside partners. Facing fish also turn broadside more frequently in the first 1·5-sec interval after they have been faced by their partners than they do in the first 1·5-sec interval after their partners have turned broadside to them. This effect can be demon­ strated for the subsequent 1·5-sec interval after the fish turns to face. The analysis does not allow a distinction between the effect of the act of facing by the partner from the facing orientation of the partner. In so far as a fish is not more likely to tum to face in the first 1·5-sec interval after its partner has faced it (Table Illb) than it is to turn to face in the first 1·5-sec interval it spends in the presence of a partner that has been facing all the while (Table Ilb), there does not seem to be an additional effect of the act of turning to face by the partner over the partner's facing orientation.

This analysis is confirmed by the following analysis of a fish in a situation where it can see its partner's display, but its partner cannot see the fish's display. The partner displays on the bright side of a 'one-way mirror', so that it sees only its reflection, which of course maintains its display. Figure 6 shows the result of an analysis of 30 min display by the fish and its partner. The ordinate shows the frequency of turning broadside by the fish (solid points and line) and the partner (open points and dotted line), in the successive 3-sec intervals after the partner and the fish (respectively) had turned to face. If either fish's act of turning to face has no effect on the other, the frequency of the other's turn­ ing broadside with respect to the first's act of turning to face should be constant from interval to interval. In fact both fish and partner are

more likely to turn broadside sooner than later after their opposite has turned to face.

~.._

0-60

~ -0

c 0 u

C>I

0-40

U1 C>I

~

£.._

~

0-20 ' 0 ·,,, ' 0 ----0

3

6

9

dull bright

12

Seconds since partner turned to face

Fig. 6. Frequencies with which two facing fish, one on the bright side, and the other on the dull side of a one-way mirror, turned broadside (ordinate) in successive 3-sec intervals after their partners had turned to face (abscissa).

However, only for the fish, which can see the partner, is the distribution of frequencies over the successive intervals significantly different from that expected by chance. (Kolmogorov­ Smirnov one-sample test, P < 0·05, two-tailed.) The apparent effect of the fish (which should be invisible to the partner) on the partner may be the consequence of the fish so 'phasing' its display that it faces at a time when partner is more likely to tum broadside anyway. These data canfiot by themselves explain fully how the fish take it in turns to face each other, because the data do not show the moment by moment changes in each fish's frequency of turning to face or turning broadside from interval to interval during their broadside and facing bouts. They merely show that when the two participants are in the same orientation (i.e. facing each other, or broadside to each other) they are both more likely to change orientation. For them to take it in turns to face each other (as the idealized Fig. Sc shows): when they assume the same orientation, as when the broadside fish in a facing-broadside

INTERACTION OF TWO DISPLAYING FISH

pair turns to face, then the fish last to change its orientation (the fish that has just turned to face) should be the less likely of the two to change it again (i.e. to turn broadside again, in this ex­ ample). Thus the partner that was originally

29

facing should now be the one to turn broadside. The same argument can be applied to the case of a facing-broadside pair becoming a broadside­ broadside pair, when the fish that was originally broadside should be the most likely to turn to

Partner is broadside

Partner is facing

a

b

0-70

;

I

.>c--..,)1(­

0-50

~~

0.10

,+

; -_.)(

;

/

I I

:

0-30

/

I

I

; ;c ./ ; ; I

)(....-x

(\

.!;

i

l5

'­

6-0

sec

1-5 JO

6-0

Partner turns broadside, & turns to face

~

(II

3-0

l<

a.

d

(II

.E .9

0-60

Ol

c

·c: '­

2 0

cc a­

0-40

(II

(11

'­

LL

0.20

Fig. 7. Frequency of turning to face (ordinate) in the 1·5 sec intervals following turning broadside in the presence of a broadside (a) and a facing (b) partner. Frequency of turning to face in a broadside fish (ordinate) in the 1·5-sec intervals after the moment when the partner turns broadside (c) nad turns to face (d). In Figs 7 and 8, solid lines refer to Fish 1, and dashed lines to Fish 2. xs refer to their behaviour on day 2, and +s to their behaviour on day 1.

30

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

Partner is broadside

Portner is facing In the first l5 sec interval, b

Q.60

-+= Q.83 -><= Q.84

).40

---+= 0-73 ---x= 0·64

0.20

Portner turns to face

d ~ 0 u <:»

l/1 ID

Partner turns broadside

J\

i )(

C

Q.60

+ )(

Q.40

+

l5 3.0

6.0 sec

l5

JO

Fig. 8. Turning broadside in the 1 ·5-sec intervals follow­ ing turning to face in the presence of a broadside (a) and a facing (b) partner. Turning broadside in a facing fish in the 1·5-sec intervals after the partner turns broadside (c) and turns to face (d) cf. Fig. 7.

face. In support of this argument, it seems reason­ able to assume that an orientation becomes more likely to end, the longer the interval since it started, and Figs. 7 and 8 show this to be so for Fishes 1 and 2, in spite of the differences be­ tween them. Thus in Fig. 8a, and in Figs 7a and 7b, after turning to face in the presence of a facing or broadside partner, fish become more

likely to change their orientations with time, at least during the first 3 sec. A more detailed analysis of the facing and turning broadside of Fishes 1 and 2. The tables show considerable differences between the be­ haviour patterns of the different fish. Figures 7 and 8 analyse the facing and turning broadside of two subjects in more detail. In these analyses,

INTERACTION OF TWO DISPLAYING FISH

the data from the 2 successive days on which the fish were allowed to interact are shown separately, with points marked by x referring to the first day, and by +, to the second day. The solid lines on the graphs refer to Fish 1, and the dashed lines to Fish 2. Thus are consistencies in the individu­ als' behaviour during the 2 days shown. The purpose of this analysis is to suggest some of the complications of the display, rather than to provide new generalizations about it. It also illustrates the ways in which the method can reveal temporal pattern in behaviour. Figure 7 describes some aspects of the fishes' turning to face. 7a and 7b refer to the same situation as does Table IIb and focus on broadside fish turning to face in the presence of a partner that is either broadside (Fig. 7a) or facing (Fig. 7b) before the fish turns broadside, and which remains facing until after the fish has turned to face again. Neither of the fish seemed to be much affected by the orientation of its partner in this respect. Note that the longer fish had been broadside, the more likely were they to turn to face, and that Fish 2 was more likely to turn to face than was Fish 1. In other words, Fish 2's broadside bouts were usually shorter than those of Fish 1. Figure 7 also com­ pares the effects of a partner that turns broad­ side (Fig. 7c) and turns to face (Fig. 7d) a broad­ side fish, in terms of the frequency with which that fish will turn to face again in successive 1·5-sec intervals after the partner's change in orientation. Note that the fish are broadside to start with, and that the reference time is pro­ vided by the change in the partner's behaviour, not the fish's. In the first 1·5 sec after the partner turns broadside (Fig. 7c) the fish is more likely to turn to face than it is in the first 1·5 sec after the partner turns to face (Fig. 7d), thus confirm­ ing the results shown in Table IIIb. But, while fish remain fairly ready to turn to face again after the partner has faced, they seem to become less ready to do so with time after it has turned broadside. Figure 8 describes the turning broadside behaviour of the two fish in the presence of

31

broadside and facing partners, and thus expands the results in Table Ila. Both fish are much more likely to turn broadside in the presence of facing partners than in the presence of broadside ones. Note that Fish 1 is more likely to turn broadside than Fish 2. Figures 8c and 8d compare turning broadside in facing fish in successive 1·5-sec intervals after the partner turns broadside and turns to face and add to the data in Table Illa, showing that a facing fish is more likely to turn broadside after being faced than after its partner turns broadside to it. In summary of the individual differences be­ tween Fishes 1 and 2, Fish 1 has shorter facing bouts and longer broadside bouts than Fish 2. Pelvic fin flickering and tail beating. So far the facing and broadside behaviour of pairs of displaying fish has been described only in terms of the readiness of each individual to face and turn broadside in the presence of a partner that faced or turned broadside at specified times. The next step is to discover how the broadside move­ ments of one fish fit in to the other's facing­ broadside cycle. The following analyses use data from experiments where the fish had com­ plete access to each other, for the Perspex screen that separated the males in the preceding analyses would prevent one fish's tail beats affecting its partner fully. In the experiment for the present analysis, eight pairs of domesticated females had complete access to each other, and were allowed to display until there was a result, with one of the fish ceasing to display before the other did. Because gill cover erection was more easily recorded than turning to face, the follow­ ing analyses must be of the interaction of gill raising and lowering in one of the fish, and pelvic fin flickering and tail beating in the other. The gills are usually raised as the fish turns to face,* and lowered as it turns broadside; and while they may sometimes be raised by a fish that does not turn to face, a fish hardly ever faces without *In the females, gill cover erections per ei;icounte~ were correlated in both winners and losers with turn':11g to face per encounter (rSs + 0·90 and + 0·93 respectively).

32

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

raising its gill covers, unless it is about to bite, and records of interaction where the fish were biting each other were not used. Fish displaying at their mirror images, or at each other through glass, may sometimes lower their gill covers before they turn broadside, but the females interacting with complete access to each other do this only rarely. It must be emphasized that the following analyses refer to a few only of the possible ways in which the displaying fish could be affecting each other. This monograph does not analyse the interactions of tail flashing, carouselling and biting fish. Pelvic fin flickering. If one fish is usually broadside while its partner is facing, and has its gill covers erect while the partner has its gill covers lowered, then it is not surprising that thirteen of the sixteen females in the experiment described in chapter 6 flickered their pelvic fins more frequently while their partners had their gill covers erect (Table IX). In seven of these fish, the distribution of fin flickers between the times when the partner had its gill covers erect and lowered was significantly different from that expected by chance on the x-squared one-sample test. However, fin flickering is not equally frequent in all the intervals after the partner has raised its gill covers. Figure 9 shows how the frequency of pelvic fin flickering (ordinate) varies with time after the partner raises its gill covers (abscissa) during the time when its gill covers are erect. Six subjects contribute to this figure. They were selected from the above­ mentioned experiment as the ones that flickered their pelvic fins more than seven times while the partner had its gill covers erect, taken over the whole watch. In each of the six fish, fin flickering was more frequent in the first 1·5-sec interval after the partner had raised its gill covers than in the second interval. (P < 0·032, in a two­ tailed sign test.) Figure 10 shows the effect of the partner turning to face in the one-way mirror situation mentioned above on the fish's pelvic fin

().8()

'"§ 0.60 L­

~ "O

~ Q.40

~ L­

~ ~ow Ci>

I I I I I

' '' ' '' ' '' I

I

I

I

I

I

--­

~ a:

''

1-5 J.O

'' &O

Seconds Fig. 9. Frequency of pelvic fin flickering in the successive 1 ·5-sec intervals after the partner raises its gill covers and while it still has its gill covers erect. Medians and ranges are shown for six fish.

flickering. The partner was on the bright side of the mirror, so that while the fish could see the partner's display, the partner could not see the fish's display. The distribution of pelvic fin flickering over the successive 3-sec intervals after the partner turned to face is different from that expected by chance (P < 0·05, Kolmogorov­ Smirnov one-sample test). If pelvic fin flickering had an effect on the ending of the other fish's gill raising bouts, fin flickers would be non-randomly distributed with respect to the ends of the partner's gill raising bouts. This was not the case in any of the six fish analysed above. Pelvic fin flickering soon after the partner raises its gill covers could merely be the consequence of the way in which the fish and its partner's gills-erect, not-erect cycles are phased. If one of the fish lowers its gill covers soon after the other raises its gill covers and if pefvic fin flickering is the first broadside movement to

INTERACTION OF TWO DISPLAYING FISH

-a> 2 0-50

.£:;

u

§ u

(>)

~ 0-30

~,_ (>)

a.

cc 0.10 ~

g

3

6

9

12

15

Seconds

Fig. 10. Frequency of pelvic fin flickering per 3-sec interval after a partner on the bright side of the one-way mirror turns to face, in successive 3-sec intervals.

occur in a fish after it has raised its gill covers, then this would be sufficiently well explained. However, on most occasions, the females, from which these data come, had lowered their gill covers just before their partners had raised theirs. (Only once in five or ten times did a female raise her gill covers before her partner had lowered hers.) If pelvic fin flickering was occurring immediately after the fish had lowered its gill covers, then many of the flickers should have occurred before the partner raised her gill covers. Moreover, if the change in pelvic fin flickering frequency in the first and second in­ tervals after the fish itself had lowered her own gill covers is compared with the change from the first to the second interval after the partner had raised her gill covers, then the change in the last case is always the greater one. In the six fish contributing to Figure 9, the maximum change in the first case (i.e. from the first to the second interval after the fish had lowered its own gill covers) was a decrease of 36 per cent, while the minimum change in the second place was a decrease of 50 per cent. Thus the partner's gill cover erection had some effect on the fish's pelvic fin flickering.

Tail beating. In a comparison of the rate of tail beating while the partner had its gill covers erect

33

and lowered, only six of the sixteen females in Table X, chapter 6, beat their tails more fre­ quently while their partners had their gill covers erect. Four of these fish did so significantly more often (Table X). Of the ten females that beat their tails less frequently while their partners had their gill covers erect, two did so significantly less frequently. Such individual differences in the tail beating while the partner has its gill covers erect could be a means by which the fish com­ municate with their partners. (Chapter 7 extends this argument.) How does tail beating frequency change when the partner raises and lowers its gill covers? This frequency was measured in the 1·5-sec intervals preceding and following the instant when the partner lowers her gill covers, and pairs of these four intervals were compared as follows: 1. Eleven of thirteen fish beat their tails less frequently immediately after their partners had raised their gill covers than they had immed­ iately before*. 2. Eleven of fourteen fish beat their tails less frequently in the 1·5-sec interval after their partners had raised their gill covers than they did in the interval just before their partners lowered their gill covers. 3. Ten of fourteen fish beat their tails more frequently in the interval before their partners lowered their gill covers than they did in the interval just afterwards. In other words, tail beating is less frequent soon after a change in the partner's gill cover position than it is just before such a change, regardless of the direction of the change. (There is also an increase in tail beating fre­ quency during the time when the partner has its gill covers lowered. Ten of fourteen beat their tails more frequently in the interval before the partner raised its gill covers than they did in the interval just afterwards.) When a fish's partner is facing, and has its gill covers erect, the fish usually flickers its *In three of the sixteen possible comparisons (sixteen females in the experiment in chapter 6) there were equal numbers of tail beats in the two intervals, and such ties are excluded.

34

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

pelvic fins first, and only if the partner keeps its gill covers erect for more than 2 or 3 sec may the fish beat its tail once or twice. If the partner still keeps its gill covers erect, the fish may then deliver a burst of tail beats, after which the partner lowers its gill covers. In its tail beating, the fish gives the impression of doing so to achieve the 'goal' partner-with-its-gill-covers­ down-again, and this impression is confirmed by the finding that the fish usually stops tail beating when the partner lowers its gill covers. Thereupon, the fish raises its own gill covers at once. (See also discussion in chapter 8.)

Although the preceding results suggest that a fish is less, rather than more likely to beat its tail after the partner has raised its gill covers, it is still possible that the fish's tail beating frequency changes over the time spent by the partner during each of its bouts of gill covers erect. In this section, changes within one of the fish's broadside bouts will be examined, while chapter 8 will analyse changes from bout to bout. If the frequency with which a fish beats its tail in the presence of a partner with its gill covers erect increases over the time after the

a

b

• =1 0 =2

•=1 0 =2 __ ..o, 0 .... '

',,

'-o--- -o,',, ',o

* a b

•=3 ; 0

•=3

=4

0

40

=4

b

• =12

30 20

10

*0-3

3-6 6-9 9-12 >12

1.5

JO

4-5

60 75

Fig. 11. (a) Frequency of tail beating per 100 sec during partner's gill raising bouts of lengths 0 to 3, 3 to 6, 6 to 9, 9 to 12 and more than 12 sec.(All the scales are the same.) (b) Frequency of tail beating per 1·5 sec interval in successive intervals after the partner raises its gill covers. (All the scales are the same.) *in a and b refers to a significantly non-random distribution of tail beats (see text).

INTERACTION OF TWO DISPLAYING FISH

partner raised its gill covers, then the overall tail beating rate by the fish should be greater in long bouts of its partner's gill cover erection than in short bouts. For those fish in the experi­ ment described in chapter 6, which beat their tails more than twelve times while their partners had their gill covers erect, the partner's gill cover erections were classified into erections with bout lengths less than l ·5 sec long, l ·5 to 3·0 sec, 3·0 to 6·0, 6·0 to 9·0, 9·0 to 12·0, and more than 12·0 sec, and the times spent by the partner in bouts of each of these classes was measured. For each class, the numbers of tail beats given by the fish were also counted. Thus for each class of gill raising bouts by the partner it was possible to calculate the fish's rate of tail beating per 100 sec, and these rates are plotted on the ordinates of the graphs in Fig. l la. For the individual fish the distrbution of tail beats was compared with the distribution ex­ pected on the hypothesis that the tail beating rate of the fish was the same, regardless of the duration of the partner's gill raising bouts. The numbers of tail beats expected to fall into each class of bouts could be calculated from the over­ all rate of tail beating by the fish while its partner had its gill covers erect, and the total time of gill cover erection contributed by the bouts in each class. In Fig. lla, an asterisk (*) by a particular graph denotes that the dis­ tribution of tail beats is significantly different from that expected on the uniform distribution hypothesis at the 5 per cent level. Figure lla suggests that the longer the part­ ner's gill raising bouts, the greater the rate at which the fish beats its tail. But these data should be interpreted with caution. They refer to a few fish only, and the rates of tail beating for the first l ·5 sec may be spuriously low for the following reason. If, after l ·25 sec of gill raising by the partner, the fish beats its tail in the next 0·12 sec, and the partner then immediately lowers its gill covers l ·37 sec after it had raised them, I am unlikely to be able to respond both to the fish's tail beating and the partner's gill lowering before the further 0· 13 sec have passed

35

-which bring the gill cover erection into the l ·5- to 3·0-sec category. Thus more gill cover erections in which the fish beats its tail may be wrongly classed as being longer than l ·5 sec than are those in which the fish does nothing. In some of the fish, tail beating rates are highest for gill raising bouts of intermediate durations. Such a result suggests t).uit the rate of tail beating reaches a ceiling after a certain dura­ tion of gill cover erection during a particular bout. Such a result could also be obtained if the bouts had to be long enough to stimulate tail beating, and if they were brought to an end by tail beating. Note that there are considerable differences in tail beating behaviour in the different fish, both in their maximum rates of tail beating, and in the bout lengths of their partner's gill cover erections that produce maximum tail beating. Figure 11b is based on an analysis of all the partner's gill raising bouts at once, in contrast to the previous analyses which separated the gill raising bouts according to their lengths. In the analysis contributing to Fig. l lb the fish's tail beating per l ·5-sec interval is shown (ordinates) in the successive intervals (abscissae) after the partner had raised its gill covers. Tail beating increases over the intervals after the partner had raised its gill covers, and in Fish 1, the dis­ tribution of tail beats into the· intervals is sig­ nificantly different from that expected by chance, at the 1 per cent level. Does a fish's tail beating influence the ending of its partner's gill raising bouts? In Fig. 12, the reference time is the moment when the part­ ner lowers its gill covers (0 on the abscissa). Unlike Fig. 11, this one refers to those 1·5-sec intervals preceding the moment when the partner lowers its gill covers, and the ordinate refers to the frequency of tail beating in those gill raising bouts in which the fish beat its tail, and excludes those bouts in which the fish did not beat its tail. Figures 11 and 12 suggest that there is a temporal relation between the fish' tail beating and the partner's gill lowering, with the partner

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BEITA SPLENDENS

36

lO

1 2

I

.

I

,'

I

I

I

'

I

0·8

.

0·6

I

,o' ,, ,,,

0.4

o··­ ..0

0.2

'i'

' '' I I

I

1.0

I

I

'

o.a

I I I

I

I I I

I

I

I

0·6 0·4

I

I I

'

I

4 I' I '

7.5 6.0 4.5 3-0 l5

0·2

Fig. 12. Frequency of tail beating per 1 ·5-sec interval in the 1·5-sec intervals preceding the moment when the partner lowers its gill covers.

lowering its gill covers a particular time after the fish beats its tail most frequently. Analyses of tail beating while the partner's gill covers are lowered, with respect both to the moment when the partner re-erects its gill covers, and the moment when it lowers them, were made for seven of the females. In six of them the peak tail beating frequency is greater when tail beating is defined with respect to the moment when the partner's gill covers are re­ erected, than it is when defined with respect to the moment when they are lowered. A possible inference is that the temporal relationships between the moment of re-erection of the part­ ner's gill covers and the fish's tail beating is more rigid than that between the tail beating following the lowering of the partner's gill cover. In other words, the partner may be raising its gill covers in response to the fish's tail beating.

6. AN ENCOUNTER BETWEEN TWO FISH longer than those of the others, and they gulped air in one place more often than did the others, and I made these two suspected males into one of the pairs. Otherwise the pairs were so selected that the two members of each pair were easy to distinguish by their colours and patterns. Thus the assignment of the fish into their pairs was not random. I recognized a third male being paired with a female, only some weeks later. But his behaviour with the female with which he had been unwittingly paired was like that of the females with females, and quite unlike that of a courting male. (In courtship the female stays in one place and at first the male makes periodic visits to her from some distance, while in the encounter in this experiment the two fish re­ mained close to each other throughout.) The histories of the members of each pair were identical so far as they could be controlled. But one group of fish constituting three of the pairs had been reared in Madingley, and had come from two groups of five fish each that had been kept in their tanks for at least a month. One fish for each of the three pairs had come from each tank. The twelve fish in the second group came from a London dealer, but they had been kept in four tanks for the 2 weeks they were in the laboratory before the experiment. When these fish were paired, no fish was paired with one of its tank-mates, so that the members of each pair were strangers in the sense that they had not seen each other for at least a fortnight. When in their tanks of three, each fish displayed to all the others in its tank. Before the fish were placed together in their 'stranger-stranger' pairs, the individuals were isolated from all other fish for 48 hr in the case of the three home-reared pairs, and for 24 hr for the remainder. Isolation ensures that fish will display in a strange tank. Clayton & Hinde (in press) found that after habituation of their display to their mirror images, domesticated males dis­ played more (in terms of the rate of challenging, for example), the longer the mirror had been

An encounter between two Bettas often gives the impression that it is a period of 'equal and mutual aggressiveness' (Braddock & Braddock, 1955), especially when the fish return tail beats for tail beats, and bites for bites. At some stage, sometimes before any bites have been exchanged, one of the fish ceases to display and begins to move away from the other, which soon stops too, and begins to follow the first. Such outcomes are almost always clear-cut. If the outcome depends on the display preceding it, it is possible that there are clear-cut differences between the displays of the two participants. This chapter describes the displays of domesticated females, during en­ counters that were allowed to continue until one of the fish ceased to display. The results were analysed to reveal how the displays of both subjects changed as the encounters progressed, and to seek differences between the individuals' displays that might be related to the outcome of their encounter. In so far as this analysis follows the progressive changes during the displays of both participants, it is similar to Oehlert's (1958) analysis of cichlid displays, and in so far as it uses previously isolated females and seeks differences between the displays of the individ­ uals concerned, it is similar to Braddock & Braddock's (1955) approach It differs from Braddock & Braddock's method in that the period of isolation was shorter, being 24 or 48 hr, rather than at least 7 days, and the fishes' sizes were indistinguishable by eye. Methods

Eighteen domesticated fighting fish, believed to be females at the time of the experiment, but found later to include males, were made into nine pairs. Like Braddock & Braddock (1955) I intended to use females during the encounters where the fish had complete access to each other because they damage each other less than do domesticated males. Before the fish were paired off, I had suspected that two of them might be males because their fins were slightly 37

38

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

removed, when it was returned. The procedure by which the fish from the two groups were introduced to each other differed in detail, but it ensured that each fish of a pair was equally strange to the tank in which they were finally allowed to interact with each other. The fish in the first group were isolated in completely separate tanks, and finally transferred to the test tank in Perspex food containers, while the fish in the second group spent their time in isolation in the two halves of the tank in which they were to be tested. They were separated from each other by an opaque screen of unplasticized Pers­ pex, which was removed to start the experiment. The problem of recording two animals at once has already been mentioned (p. 6). Such recording is difficult, and must be inaccurate and subject to bias. In two senses, however, this recording was blind. There were no extant hypotheses about the display differences expected in the fish, because the experiment described in chapter 7 had not been done; and I had no fore­ knowledge of the outcome. This is in any case so difficult to predict that the males' display is the subject of organized betting in Bangkok (Smith, 1937). After the event, I found that equal numbers of winners and losers had been re­ corded by each of my hands, so that bias in the display records due to my 'handedness' should have been minimized. For each individual, pelvic fin flickering, tail beating, gill cover erection and lowering, turning to face and turning broadside, and tail flashing were recorded. Because tail beating occurs only when the fish is broadside, and not facing, it can be recorded on the facing key, and pelvic fin flickering, which occurs only when the fish is broadside, was re­ corded by means of repeatedly releasing and pressing the broadside key, thus making a hatched mark corresponding to the duration of the fin flickering bout. The fish were not measured. They looked about the same size. In thirty of the Braddocks' thirty-five pairings, the fish were of different sizes, and the larger fish won in twenty-seven of these.

Results Eight of the nine encounters led to clear-cut outcomes, but the ninth had to be stopped after about 40 min, when the fish had just spent nearly 1 min on the bottom, locked mouth to mouth, and in danger of drowning. The briefest en­ counter lasted less than 4 min, and the longest about 14 (Table V). The 40-min 'draw' was ex­ cluded from the subsequent analyses. Table V. Summary of the Colours, Durations of Encounters and Outcomes for the Subjects Contributing the Data for this Chapter It is possible that further work will reveal relations between the displays and colours of domesticated Betta

Fish

Duration of the encounter

Colour

min

1 2

Mainly blue, some green on fins} Green, some blue streaks on fins

3 4

Blue, some red on fins Reddish brown

6

5

Blue Green

7 8

Blue, red fins Green, red bases to fins

9

Bright cobalt blue Smokey grey-blue

} } } }

12

11

Red-brown Blue, yellow bases to ventral and pelvic fins

}

14

13

As2 Blue-brown

15* 16*

Green Green

} }

x

Blue, some green in body and fins Mainly blue

}

10*

y

sec

13 00 9 15 13

()()

6 38 5 30

8

()()

6

()()

3 40 Draw-en­ counter was stopped by observer after40min

In each pair, the top fish is the winner, and males are marked with •. 'Blue', when unqualified means a saturated blue, which looks ultramarine in some lights, almost turquoise in others. 'Green' unqualified means a saturated emerald green.

In the eight encounters to be analysed here, the median duration lay between 6 min 38 sec and 8 min (Table V). In Braddock & Braddock's

AN ENCOUNTER BETWEEN TWO FISH

experiment, the median duration was between 30 and 45 min (and the mean was 51 ·5 min). Their fish had been isolated for at least 7 days, and Clayton & Hinde (in press) and Laudien (1965) have shown that male fighting fish become more ready to display in a display-eliciting situation over time after having been isolated. Braddock & Braddock distinguish two phases in an encounter after the initial short period before there are any 'social' reactions. First there is the 'period before the fight' when the fish are displaying, and the 'fight proper' starts with the first rapid exchange of bites. In Brad­ dock & Braddock's work, the median duration of the period before any 'social reactions' occurred was less than 15 sec, and I found that by the time I had moved from the tank, into which I put the fish, to the recorder, the fish had begun to display. For Braddock & Braddock's fish, the median duration before the first rapid

39

exchange of bites was between 4 and 6 min, the mean being 6·6 min. Table VI summarizes the biting behaviour of the fish in the present ex­ periment. In these encounters, the quality of the inter­ action changed little after the first rapid ex­ change of bites, as any subsequent exchanges were short-lived. In the more prolonged en­ counters in Braddock & Braddock's experiment, the fish may have begun to bite more contin­ uously. From Table VI it can be seen that the first rapid exchanges occurred between the 4th and the 8th min, as would be expected from Braddock & Braddock's results. Since these exchanges were rather isolated, and not followed by any obvious change in the behaviour, the distinction between a 'fight proper' and a display is not used in the analyses in this chapter. If the difference in overall duration between the en­ counters recorded by Braddock & Braddock

Table VI. Total Number of Times the Different Subjects Turned to Face, Raised Their Gill Covers, and Gave Single Bites Separate bites could not be counted in the rapid exchanges, whose times of occurrence are also shown in the table. Fish

Faces

Gill covers erections

Separate bites

First bite at min sec

Rapid exchanges at min sec

1

46 52

58 64

2 6

8*

8

4

3

53 28

56 43

8 0

3 7

7 40 &8min

5 6

21 39

42 47

4 2

2 2

7

17

23 43

6 5

3

2

8

9

35

13

3

26

10

29

40

20

4 2

3 3

12

11

28 29

42 34

2 2

2

30 46

13

16

25 20

4

44 44

15 16

18 9

17

14

10

10

5

4 4 0

6 40

4 44

2

*When the time is given to the nearest minute, the exact time at which the fish bit is not clear on the record. This is so because bites, being relatively rare, were un­ expected, and although noted within a few seconds of their occurrence, were not always noted at the exact time of their occurrence.

40

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

and those described here reflects the greater period of isolation of the females by Braddock & Braddock, it is interesting that some of the fish bit as early as those of Braddock & Braddock, but that the encounters were 'decided' with­ out prolonged periods of biting. One effect of isolation might be to increase the amount of displaying a fish will do. Although the Braddocks found that in the prolonged encounters the winners-to-be bit and

Figure 13 shows the number of sec spent per 2-min period with the gill covers erect, by the different subjects in the successive 2-min periods of their displays. (Winners have the solid points and continuous lines.) Figure 13 suggests that winners always, and losers sometimes, increase in this measure with time; and the two fish diverge in this measure towards the end of the encounter. Over the whole encounter, six of the eight winners had their gill

Table VII. Number of Times per 2-min Period that the Gill Covers Are Erected

Last

Mean for whole watch

11 14

10 10

8·9 9·8

8 9

13 9

16 8

12-1 9·3

9 14

3 10

9 7

14 2

6·0 6·7

7 8

5 6

9 17

9 17

5 18

7-7 14·3

9 10

7 19

10 18

10 18

5 5

7·3 14·6

11 12

5 8

12 15

16 7

9 4

10·5 8·5

13 14

7 2

7 9

7 9

11 9

8·4 5·3

15 16

6

14 8

-

14 8

10·9

10

10·5

8·7

8

8·9

0-2

2-4

1 2

8 5

6 7

3 4

10

11

5 6

Fish

Median for winner Median for loser

5 7

7

8·5 9·5

challenged twice as often as the losers, this was not the case with the females in this experiment, as Tables VI and VII show. Another possible measure of a fish's ability to win an encounter is the proportion of the time it spends with its gill covers erect. Gill cover erection often coincides with turning to face; and the persistence with which a fish continues to face and hold its gill covers erect once it has turned to face could be a measure of its readiness to approach its partner, by the arguments in chapters 5 and 7.

Penultimate

9

7-1

covers erect for longer than their partners, the median percentage of the time spent by the winners with their gill covers erect being 33·7, while that spent by the losers was 15·8. This difference was not significant by the Mann­ Whitney U test, two-tailed. (This test is used in all comparisons between the two groups of fish. Thus the winners and losers are being treated as two independent samples.) For statistical treatment of the gill raising behaviour, the 2-min periods in the encounters were classified as first, second, last, and penul­ timate ones (Table VIII).

41

AN ENCOUNTER BETWEEN TWO FISH

t

seconds/ 7120

13&

1&2

80

1>

60 40 20

I

*

I

I

I

0

*

cf

o,

0

5 & 6

/

....

'

I

0

0 I \

\ \

\

'o

9 & 10

o..........

0

'o,

-,o---O---o'

/

/ '

\

'o

11

& 12

~.

7& 8

6 minutes 2 4 Fig. 13. Seconds per 2-min period (ordinate) spent with gill covers erect by winners (solid points and continuous lines) and losers (open points and broken lines), in successive 2-min periods (abscissa). The first number in each graph refers to the winning fish of the pair. *=the 2-min period with the first rapid exchange of bites. ! =the proportion of the time spent by the fish was cor­ rected to seconds per 2-min period, even though the last period was not a full 2-min one.

Winners and losers were compared in all the 2-min periods, but they differed significantly only in the last one (U = 3, P = 0·002, nl = n2 = 8). The remaining results refer to the within­ fish changes, from 2-min period to 2-min period. (1) In the group offish as a whole, the increase from the first to the second period is significant (Wilcoxon matched-pairs signed-ranks two-

tailed test, P = 0·01, N = 14); and so is (2) the increase from the first to the last 2-min period (P = 0·02, N = 16.) (3) In the winners alone, the increase from the first to the second 2-min period is significant (P = 0·05, N = 7); and so is (4) the increase from the first to the last i. min period (P = 0·02, N = 8), but not

42

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS Table VIII. Seconds Spent per 2-min Period with the Gill Covers Erect The first fish in each pair won the encounter

Fish

0- 2

2- 4

Penultimate

Last

1 2

32 19

35 59

35 28

62 46

30·5 33·7

3 4

25 48

33 62

53 82

30

55

49·6 34·0

6

5

43 29

42 18

69 32

98 6

12·4 39·5

7 8

13

21 32

21 32

48 18

15·8 20·0

9 10

40

11

65 39

65 39

69 31

41-2 36·1

11

10

5

42 28

93 10

88 6

10·2 11 ·9

14

13

38 4

75 29

75 29

53 56

24·7 46·1

15 16

39 21

61 8

61 8

12·7 18·7

Median winner

28•5

42

65

62

14·3

Median loser

20

32

32

30·5

33-9

12

7

(5) the increase from the second to the last period. (6) In the losers alone, none of these increases is significant. Thus the winners finally outstrip the losers in the proportion of the time they spend with their gill covers erect. But the whole group of fish increases the proportion of time spent with the gill covers erect, and in this sense both winners and losers can be said to be equally aggressive. If the proportion of time the fish spend with their gill covers erect changes from 2-min period to 2-min period, does this reflect an increase in the frequency with which the gill covers are erected? Over the whole encounter, fish did not come to raise their gill covers more frequently (Table VII). But in the second 2-min period, seven of the losers-to-be raised their gill covers more often than did their partners. Braddock & Braddock (1955) found that, in fights between females that lasted more than 60 min, potential winners raised their gill covers (challenged) and bit· twice as often as potential losers. This

Per cent of whole watch

result is not directly comparable with those presented here, because none of the fish in the present experiment displayed for longer than 15 min. If, over the encounters studied in this experi­ ment, fish come to spend a greater proportion of their time with their gill covers erect, but do not increase the frequency with which they erect them, then this change must reflect an increase in the bout lengths of the individual erections. And, at the end of the encounter, winners' gill cover erections are longer than those of their partners. The greater duration of the winners' bouts of gill cover erection may reflect a decrease in responsiveness of their gill cover lowering to their partners' displays, or a difference in their partners' displays, such as a decrease in their tail beating, while the fish have their gill covers erect. Chapter 5 showed how a facing bout of a fish separated from its partner by a transparent screen was more likely to end after its broadside partner had turned to face too. But the females,

AN ENCOUNTER BETWEEN TWO FISH

43

tail beating by the losers. However, Fig. lla and 11b in chapter 5 show that, at least in some subjects, the rate with which a fish beats its tail during one of its partner's gill raising bouts in­ creases the longer the bouts are, so that longer bouts could lead to greater overall tail beating frequencies. Figure 14 shows how tail beating frequency in the time that the partner has its gill covers erect varies with the proportion of the whole watch for which the partner had its gill covers erect. (Values of this measure of tail beating in Table X). Closed circles refer to the tail beating of the winners over the whole watch, and open circles to the losers' tail beating. For the winners, the longer the partner spends with its gill covers erect, the more frequently do they beat their tails (rS = 0·64, ns), but for the losers the opposite is the case, with tail beating frequency negatively correlated with the

displaying with complete access to each other, seldom turned to face and raised their own gill covers before their partners had turned broad­ side and lowered their gill covers. If one of the fish lowers its gill covers and turns broadside while its partner is still broadside, then it is possible that the partner's broadside display can affect the fish's gill cover lowering. The previous chapter showed that a broadside fish may flicker its pelvic fins and beat its tail after its partner has raised its gill covers. The following analysis compares the tail beating of winners- and losers-to-be. Over the whole en­ counters the rates of tail beating per 100 sec spent by the partners with their gill covers erect were measured. Seven of the eight losers had greater rates than did their partners. It seems that in these fish, their partners' gill raising bouts eventually became the longer in spite of more 50

Winner=• Loser =o 0

0

40

0
D

c:

8 30

•

""


0

•

0

S::' ....

• •

""CL 20


0

0

•

""

Ll

·­

r9

10

•

•• 10

20

°lo of encounter spent

0

0 0

30

40

by partner with its gill covers

50

erect Fig. 14. Tail beating frequency (tail beats per 2 min) while the partner has its gill covers erect, for different winners and losers, plotted against the proportions of the whole encounters for which their partners have their gill covers erect.

44

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

proportion of the watch spent by the partner with its gill covers erect (rS = - 0·88, P = 0·01 to 0·001). It is tempting to suggest that the winners increase their tail beating rates the longer their partners hold their gill covers erect, while the losers fail to do so. The negative correlation found for the losers could simply be the conse­ quence of a constant number of tail beats by the losers, and different proportions of time spent with their gill covers erect by the winners. Tables IX and X show the frequencies with which the fish flicker their pelvic fins and beat their tails. They also show the frequencies of these movements during the time when the part­ ners had their gill covers erect and lowered, measured over the whole encounters. It can be seen that the variation in these measures from fish to fish, and from pair to pair, is considerable. This chapter has examined only a few frag­ ments of the interaction, and it has barely men­

tioned such aspects as carouselling, tail beating by the fish when their partner's gill covers are lowered, and the ways in which they exchange bites, all of which may be relevant to the out­ comes of the displays. Because it is possible that different broadside displays may have different effects on the partner's behaviour, the next chapter describes an experiment where the broadside display is examined in more detail. Differences in broadside displays have been difficult to interpret so far, because of the possibility that the fish whose broadside display is being studied may be affecting the behaviour of the partner which is eliciting it, and so may be changing the eliciting situation moment by moment. In the next chapter the partner is a stationary puppet, and is thus independent of the fish in its behaviour. After an encounter, the participants have changed in several ways. They no longer display

Table IX. Number of Times the Pelvic Fins Are Flickered per 2-min Period Fish

0-2

2-4

Penultimate

Last

1 2

2 2

4 4

0 3

0 2

3 4

6 13

8 16

6 14

5 6

11

5

8 4

7 8

6 13

9 10

Mean for whole encounter

Rate per 2 min while partner has gills not erect erect

4-1

1·2

2·5 3·7

11

6

6·9 13-8

9·6 24·2

9 6

2 6

5·6 4·4

18·6 6·5

13 8

(13) (8)

12 5

11-3 9·3

23-2 10·0

5 10

3 16

(3) (16)

3 12

13-8

3-6

6·2 21·2

11 12

1 13

4 25

4 21

4 22

3-3 20·2

7-3 97·0

13 14

13 0

12 9

(12) (9)

19 3

14·7 3·6

18·9 4·3

15 16

12 11

13 9

13 9

13·1 10·5

12·9 11-7

6

8

6

7'5

6·3

11-3

3-6

10·5

12·5

9

7'5

9·9

10·9

9·1

Median winner Median loser

0·7 4·6

•

• •

•

• • •

4·3 8·5 2-8 3-3 7·9 9·9 2-1

9·7

2-3

12-8 13'3 2·6

•

13-8 17·5

*=distribution of fin flickers between the time when partner's gills are erect and lowered is different from that expected by chance at the 5 per cent level.

45

AN ENCOUNTER BETWEEN TWO FISH Table X. Number of Times the Tail is Beaten per 2-min Period

Rate per 2 min while partner has gills not erect erect 29·4 4·6 23·7 30·6

Fish

0-2

2-4

Penultimate

Last

Mean for whole encounter

1 2

12 9

15 17

11 48

14 26

12'1 26·9

3 4

20 6

9 13

18 11

2 5

18·8 10·2

25·3 7·6

6

5

12 12

3 13

24 11

10 6

6·6 6·0

4·6 4·7

7 8

43 33

31 30

(31) (30)

39 21

37-8 28·0

21·0 36·6

9 10

18 46

29 31

(29) (31)

3 11

17-8 30·9

15·0 18·2

•

19·8 38·1

•

5·8 5-1

•

10

5

9 12

5

12

8

4 8

5·8 9·5

4·9 42-1

13 14

12 21

8 9

(8) (9)

8 8

9·3 12-7

5·4 8·0

15 16

19 27

20 33

20 33

21·4 41·9

Median winner

15

12

30·0 19·6 15·0

11

18

9

18·0

•

14·3 11-5 6·8 5·7

•

35·3 26·8

10·1 16·7

•

31-3 14·8 12·2

24·2 16·2 15-6 11 9·5t 15 16·5t Median loser that from different is lowered and erect are covers gill partner's the when time the between beats tail of •=distribution expected by chance at the 5 per cent level. t -if the first and last 2-min periods for the sixteen fish are matched, the tail beating frequency in the last 2-min period is significantly different from that in the first. (P < 0·05, Wilcoxon matched-pairs test, two-tailed).

to each other, at least while they are still to­ gether in the same tank on the day of the first encounter. Five of the pairs of fish used in the observations described in this chapter were left together after their encounters for 2 hours, after which they were watched for 5 min, to see which fish was dominant (e.g. methods, p. 12). Once the fish were within a length of each other, none of the original winners moved away to increase this distance more often than their partner. And it was always the winner that had originally caused this inter-fish distance to close. In other words, the winners did relatively more approaching, and less leaving than their partners. It could be argued that the fish were still tired and did not display for this reason. How­ ever, if they are presented with a mirror immed­ iately after an encounter, the winners display vigorously, although the losers do not even raise their gill covers (in thirteen pairs of fish tested thus), although both fish may push each other

aside in their efforts to get near the mirror, to look into it. The change in the losers is not only due to fatigue, for they will display as vigorously as their partners if they are replaced in their 'home' tanks immediately after their encounter -when they display to their original neighbours in turn. Thus the change in the losers, such that they no longer respond to their mirror images, may be specific to the mirror. It may be that the losers require the 'partner' to initiate further display (and of course the partner must be a fish other than the one which has just defeated them). That the loser's responsiveness only changes at the end of their encounters is suggested by an experiment with five pairs of fish, whose en­ counters were stopped after 5 min so that the fish could be tested separately with mirrors, when both winners- and losers-to-be displayed to their mirror images; although, in these five pairs it was the winner-to-be that turned to face its mirror image more frequently.

7. VARIATION IN THE DISPLAY FROM INDIVIDUAL TO INDIVIDUAL If the pattern of display varies from individual to individual, then it is possible that an in­ dividual's display may communicate something about itself. The way in which the display varies might suggest the extent to which it is capable of communicating. An attempt to analyse such variation is described here. It starts with the assumption that the display reflects the readiness of a fish to approach another fish, and it seeks correlations between measures of the display and the proportion of the time the displaying fish spends near a stationary puppet. Such measures as are correlated with this may dis­ tinguish winners- from losers-to-be in encounters that are allowed to run to their conclusions. If fish give all the display movements many times over during their displays, then their displays will vary in the temporal patterning of these movements-perhaps in their frequencies relative to each other, perhaps in more elaborate patterns, such as their sequences. By definition, a temporal pattern can only exist in a finite time span. Most of the analyses so far have been restricted to relatively short time spans-such as the 1·5 sec following a change in the partner's display, but some analyses have found patterns over the 3 to 6 sec of whole broadside bouts (e.g. Fig. 4), or over the time when the partner has its gill cover erects or lowered (e.g. Fig. 11 b). This chapter examines such pattern& in a differ­ ent way, by looking for variation in frequencies of occurrence of broadside movements relative to each other, and for the frequencies of these movements per facing-broadside cycle. If such variation from fish to fish is orderly-perhaps with those fish that spend most time near the puppet, flickering their pelvic fins more and flashing their tails less-then it is possible that, in interactions with real fish, the relative fre­ quencies of these movements affect the partner. The experiment described here examined display variation between and within fish in a situation where their display could not affect that of the fish eliciting them. It was expected

that different fish would spend different propor­ tions of their time near the puppet, and that their display would differ correspondingly. Within-fish variation was produced by having the puppet alternate the facing and broadside orientations. It was assumed that a change in the puppet's orientations would produce a change in the fishes' readiness to approach, with cor­ related changes in their displays. For example all fish might be more frightened of a facing puppet. It was expected that between-fish variation would run in the same way, so that a between-fish difference correlated with a differ­ ent proportion of time spent near the puppet would be of the same kind as a within-fish difference, correlated with the different propor­ tions of time spent near the puppet when it was facing and broadside.

Methods The subjects (Table XI) were eighteen adult male domesticated fighting fish. They were all of about the same age, but not all had had the same experience of displaying. Since this experi­ ment required a diversity of displays to provide enough variation for tests of correlation between display measures to be possible, and since the object of the experiment was not to separate the genetic and environmental antecedents of the variation, anything contributing to this diversity was welcomed. The fish were kept in the tanks in which they were to be tested. Some were kept in whole tanks (p. 5), others in half tanks (Table XI). The fish could not see their neigh­ bours. On each of the 6 days before a fish was tested, it was treated in a way that had been found to enhance its responsiveness to display-eliciting stimuli (Heiligenberg, 1965, and personal com­ munication from Hogan & Burne!). Every day each fish was shown its mirror image until it had turned to face about three times, or until it had approached to within about 4 cm and gone away again, whichever occurred first. About 5 46

VARIATION IN THE DISPLAY FROM INDIVIDUAL TO INDIVIDUAL Table XI. The Colours of the Fish Used as Subjects in the Experiment and whether or not They Built Nests in Their Tanks; also whether the Test Tanks Were Whole- or Half-tanks In a whole-tank, the volume of water 'near' the puppet is 11 ·5 per cent of the whole, while in a half-tank it is 23 per cent. Other things being equal, the fish would be expected to spend corresponding proportions of their time near the puppet (cf) Table XII). Fish Colour Nest Tank

Bright blue, red fins + 1 Bright blue ! Blue-green + ! 4 l)ark blue + 1 5 Smokey blue-grey 1 6 as 3 7 Green 1 8 Smokey blue-grey 1 9 Green + 1 10 Blue ! 11 Blue, red tail + 1 12 Green, red fins ! l3 Red* + ! 14 l)ull crimson-maroon* + ! 15 Red, blue fins + 1 16 Red + 1 17 Bright blue ! 18 Red ! *For the definition of green and blue, see Table V. 'Red' is between burgundy and cherry red, and crimson­ maroon the colour of freshly dried blood. 1 2 3

min later the fish was shown the puppet, which was held by hand outside the tank, and moved about until the fish had turned its eyes towards it. Then the puppet was held stationary until the fish had faced about three times, or approached and gone away, whichever occurred first. On the occasions when a fish never came near the pup­ pet, the puppet was merely held outside the tank for! min. Different subjects were tested at different times of day, six fish being tested a day over a period of 3 consecutive days. The Test Situation On the 7th day after the above-described 'priming' had begun, the fish were given only the mirror, and then a white sheet of paper was placed outside the tank where the puppet was to be placed. Three min later the paper was re­ moved, revealing the puppet in a broadside orien­ tation. Recording was begun at once, and 2 min later the puppet was made to face, by pressing one of the keys on the event recorder, which switched a solenoid rotating the puppet through

47

its supporting rod (Fig. 15). The key also acti­ vated one of the pens on the recorder. After the puppet had faced for 2 min, it was turned broad­ side again, and thus its orientation continued to change every 2 min throughout the 40-min test. The puppet's gill covers and pelvic fins remained erect throughout the whole test. (A real fish withdraws its pelvic fins when it turns to face, and lowers its gill covers when it turns broadside.) Figure 15B shows the shape and colours of the puppet. The puppet was so pivoted that when it was broadside its flank was as far from the tank as its snout had been when it was facing. The puppet (Fig. 15B) had a sealed balsa body, which was oil-painted and varnished. The black eyes, gill covers and the cross bars on the dorsal fin were black polythene, and the bright scales and flashes on the fins and eyes were cut from the shiny wrapping of a confection called Buttercrunch. The side of the body to be presented to the fish was rounded and painted, as was the whole head, but the other side of the body was open, to hold the mechanisms by which movements were transmitted to pelvic fins, gill covers etc. in other experiments. Figure 15A shows how the solenoids were connected to the rod supporting the puppet. (The cores of the solenoids were cut from nails, and they rested in Tufnol reels, shaped on a lathe, and 200 turns of insulated 32-gauge wire were wound on to the reels. Direct current was provided by dry cells. Full details of these and other aspects of the puppet's design and construction are in Simpson (1966).

Recording Six pens of the time-event recorder were used. Turning to face, tail flashing, tail beating, turning broadside, gill cover erection and biting were recorded according to the criteria described under Methods, and on p. 13 et seq. The time the fish spent within its own length of the puppet was also recorded. This was easy because the fish approached and left the puppet quickly.

48

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

A

6

B

Fig. 15. B shows the side of the puppet visible to the fish, and A the arrangement of the solenoids which change its orientation. The puppet is 7 ·4 cm long, and the solenoids are drawn to the same scale, but are viewed from above, so that the 10-cm rod supporting the puppet is shown end-on in A. In B, 8 is the transparent plate on whose back parts of the mechanisms working the puppet's moving parts were mounted. The rod (6) is inserted into a cork screwed on to the plate, to make an adjustable and detachable mount. In the diagram of the puppet itself, white is velvety black-brown, solid black is black polythene, stipple is crimson-red, vertical hatching is ultramarine­ blue and diagonal hatching is blue-green shiny Butter­ crunch paper. The puppet's pelvic fins had white tips. In A, the rod supporting the puppet (6) (viewed from above in this part of the diagram) was turned to the position shown when current was passed in the coils (1) of the solenoid, thus drawing the rod (2) towards the centre of the Tufnol reel on which the wire was wound. With it, the rod pulled the rubber strip (3), through which part of an entomological pin (4) was stuck. This pin fitted into a hole in the grub screw (5), which was firmly at­ tached through the bush wheel to the rod (6). The rubber strip (3) also drew the other rod (7) out of its solenoid. The positions of the rods (7 and 2), and thus the orientation of the puppet, were reversed by passing current in rod 7's solenoid.

Analysis Fin flickering, tail beating and tail flashing were expressed as frequencies per broadside bout. The frequencies of these components were also expressed as frequencies with respect to each other, so that the relative frequency of fin

flickering is, for example, sum of fin flickers during the test total fin flickers + tail beats + tail flashes The analyses in this experiment refer to the results of the whole test for all the fish except Fish 1, which turned to face and turned broad­ side much more frequently than did the others, so that by the 8th min it had faced 118 times, compared with the median of 72 times for the whole group's display over the 40-min test. Because Fish 1 seemed more 'fatigued' halfway through the test (by which time it had turned to face more than 200 times) than the others seemed at the end, only the first 8 min of 1's display were used for the analysis. Fish 3 is treated in the analyses as if it were two individuals, 3a and 3b. In the first 12 min of its test, 3 spent most of its time away from the puppet (Table XII); then it approached the puppet and stayed for the remaining 28 min. Although the periods during which 3a and 3b were watched are different from those during which the other fish were watched, the numbers of facing-broadside cycles are comparable (Table XII).

Results The behaviour of every fish was affected by the presence and movements of the puppet in some way although not all of them displayed to it. Two of the three non-displayers (Fishes 18 and 19) spent all their time away from it, while 17 approached it and examined it closely. None of these three fish raised their gill covers, or spread their fins in the puppet's presence, al­ though Fish 19 flashed its tail a few times. When the puppet changed orientation the first six times, 19 darted violently towards the bottom of the tank and stayed near that wall furthest from the puppet. Fish 18 made four approaches without ever coming within its own length of the puppet, and 18 reacted distinctly, but less violently than 19 to the puppet's changes in orientation. In contrast to 18 and 19, Fish 17 spent more time near the puppet than would be expected had it distributed its time between the

VARIATION IN THE DISPLAY FROM INDIVIDUAL TO INDIVIDUAL

49

Table XII. Percentage of Time the Fish Spend Near the Puppet and with Their Gill Covers Erect, and the Number of Times They Turn to Face it, When it is Broadside (br) and Facing (f) The fish are numbered according to their ranking in the proportion of the whole test they spend with their gill covers erect Fish

%time gill covers

%time near

erect

f

No. of times the fish faces f br

br

f

br

100

100

93·0

93·0

55

63

(1 *

97

97

65-6

75·4

207

274)

2

100

100

68·0

79·8

51

63

3••

100

100

44·0

63-3

46

110

4

70

63

41·7

37·6

24

21

5

25

32

44·2

31-2

46

53

6

17

41 ·1

17·2

28

18

7

90

25·9

27-9

37

46

6·0 90

8

5·4

6·7

20·2

20·7

41

36

9

1·8

1·5

10·8

16·3

23

20

10

3·0

2·5

13·0

9·4

29

31

11

3-8

1·8

12·0

7·5

47

27

12

11·6

1·5

13-3

5·7

40

31

13

4·1

2-7

8·2

6·9

43

32

14

1-2

0·5

7·4

4·9

42

11

15

1·4

2·8

4·4

3-6

58

42

0·0

0·0

10

4

O·O

0·0

0

0

16 17

16 0·0

15 0·0

• Refers to l's behaviour measured over the whole watch. **Refers to Fish 3 in the last 28 min of the test, and 6 is the same fish during the first 12 min.

volumes of the spaces 'near' and 'away' by chance. The remainder of this description refers to those fish that did display to the puppet. All of them erected their median fins fully at some time in the presence of the puppet, and all raised their gill covers at least once. Of these fifteen fish, one (Fish 16) is excluded from some analyses because it never beat its tail or flickered its pelvic fins. The fish's behaviour regardless of the puppet's orientation. A measure of a fish's readiness to

approach the puppet is the proportion of the time it spends near by, and this is positively correlated with the proportion of the watch spent with the gill covers erect (rS = 0·89, P < 0·001 *) and with the number of times the fish turned to face in the whole watch (rS = 0·45, ns). This last measure, of the total number of facing-broadside cycles the fish went through varies from 43 in Fish 6 to 481 in Fish 1 (Table XII). *All the probabilities given in this chapter are for two­ tailed tests. The degrees of freedom for the correlation tests are 13. (N = 15, because Fish 3 is counted as two individuals, but Fish 16 is excluded).

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

50

Such correlations are hardly surprising since the longer a fish spends near the puppet, the more time will it also spend displaying. (These results are also confirmed by the behaviour of four fish each of which was allowed to display to a mirror for 14 days. Over a series of watches, the proportion of time spent near the mirror, the proportion of time with the gill covers erect, and the proportion of time with the median fins erect were correlated with each other, in each of the fishes (See also Simpson, 1966). The frequencies per broadside bout of pelvic fin flickering, tail beating and tail flashing vary widely from fish to fish, as Tables XIII, XIV and XV show. These frequencies were tested for their correlations with the proportion of the whole watch the fish spent with their gill covers erect, and they were also tested for their correlations with each other. With the proportion of time spent with the gill covers erect, pelvic fin flicker­

t

°lo broadside movements as tail flashes - o

70

and pelvic fin flickers-• 0

•

60 50

•

•

30

•

0

10 80 60

100

••

0

0

0

0

•

40

20

• •

• • 10

4

°lo of test spent with gill covers erect x 100 tail flashes 16 tg. · tail flashes + pelvic fin flickers + tail beats (ordinate) in fish which spent different proportions of the whole watch with their gill covers erect (abscissa), shown by the open circles. Note that the abscissa is logarithmic. The filled circles refer to the percentage of broadside movements that are pelvic fin flickers.

F'

Fish

Pelvic fin flickers

Pelvic fin flickers per facing-broadside cycle

Puppet broadside facing

Puppet broadside facing

l*"'

56

59

1-02

0·94

2

67

113

1-31

1-79

3

62

128

1-35

1-17

4

87

101

3-62

4-81

5

84

110

1-83

2·08

6

35

26

1·25

1 ·45

7

40

57

1·08

1·24

8

58

62

1·41

1-72

9

44

34

1-91

1-70

10

52

28

1 ·79•

0·90

11

53

51

1·13•

1-89

12

57

23

1·43•

0·74

13

27

19

0·63

0·59

14

21

15

1·05

1·27

15

29

32

0·50

0·76

*The distribution of fin flickers between the broadside bouts when the puppet is broadside and facing is different from that expected by chance at the 5 per cent level, by the x-squared one-sample test. **In this, and in Tables XIV and XV, the behaviour of 1 during the first 8 min of the test is shown.

0

• 00

0

0

0

0

0

0

• •

•

40

20

0

Table XIII. Number of Pelvic Fin Flickers, and Number of Pelvic Fin Flickers per Broadside Bout, When the Puppet is Broadside and Facing

ing was positively correlated, not significantly (rS = 0·45), tail beating negatively correlated (rS = - 0· 14, ns) and tail flashing negatively correlated (rS = -0·74, P < 0·001). The cor­ relations between the frequencies of the com­ ponents of the broadside display for the whole watch are: 1. Pelvic fin flickering per facing-broadside cycle and tail beating per facing-broadside cycle, rS = + 0·30, ns. 2. The same measures of pelvic :fin flickering and tail flashing, rS = + 0·16, ns; and 3. tail beating and tail flashing, rS = + 0·71, (P < 0·01 to 0·001).

VARIATION IN THE DISPLAY FROM INDIVIDUAL TO INDIVIDUAL Table XIV. Tail Beats, and Tail Beats per Broadside Bout, When the Puppet is Broadside and Facing

Tail beats per broadside bout

Tail beats

Fish

Puppet broadside facing

51

Table XV. Tail Flashes, and Tail Flashes per Broadside Bout, When the Puppet is Broadside and Facing

Fish

Puppet broadside facing

Tail flashes per broadside bout

Tail flashes Puppet broadside facing

Puppet broadside facing

1••

24

18

0·44

0·29

2

27

29

0·40

0·46

3

45

120

0·98

1·08

4

23

18

0·96

0·86

5

41

38

0·89

0·72

6

26

24

0·93

1-50

7

31

34

0·84

0·74

8

90

90

2-20

2-50

9

167

165

7-26

8·25

10

77

32

2·66

1·03

l1

122

118

2·60*

4·73

12

75

67

1'88

2'16

0·28

13

47

46

1·09

1·44

1·40

1·00

14

37

29

1 ·85*

2-64

1 ·15*

1-90

15

263

210

4·53

HO

34

49

0·62

0·78

2

22

38

0·43

0·60

3

42

104

0·91

0·95

4

32

36

1-33

1-72

5

37

54

0·80

1-02

6

19

18

0·68

1·00

7

l1

16

0·30

0·35

8

39

55

0·95*

1-53

9

68

60

2·96

3·00

10

54

27

l ·86

0·87

l1

119

89

2·54

3-30

12

22

13

0·51

0·42

13

24

9

0·56*

14

28

l1

15

67

80

• The distribution of tail beats between the broadside bouts when the puppet is facing and those when the puppet is broadside is significantly different from that expected by chance, at the 5 per cent level, by the x­ squared one-sample test. ••see Table XIII.

• The distribution of tail flashes between the fish's broadside bouts when the puppet is facing and when it is broadside is significantly different from that expected by chance, at the 5 per cent level, by the x-squared one­ sample test. ••see Table XIII.

Note that while this measure of tail beating is correlated with tail flashing, which is negatively correlated with the proportion of the time spent during the whole watch with the gill covers erect, tail beating is not itself significantly negatively correlated with the time spent with the gill covers erect. In other words, tail beating behaviour per broadside bout may, in certain respects, be con­ trolled separately from the tail flashing and gill raising behaviour. Tail flashing frequency can be regarded as an inverse measure of the fishes' readiness to approach the puppet. The frequencies of the broadside display components relative to each other, as opposed

to frequencies relative to the facing-broadside cycles, may also have signal value. Figure 16 shows the relative frequencies of the broadside components pelvic fin flickering and tail flashing, expressed as the percentage of the total broad­ side movements occurring in the whole test (p. 48, see also Table XVI). The ordinate shows the frequencies, and the abscissa the proportion of the test which the fish with each of the fre­ quencies spent with their gill covers erect. Tail flashing as a percentage of the total broadside movements is negatively correlated with the pro­ portion of the test spent with the gill covers erect (rS = - 0·89, P < 0·001), and this measure of

52

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS Table XVI. Pelvic Fin Flickering, Tail Beating and Tail Flashing as Percentages of (Total Fin Flickers + Tail Beats + Tail Flashes) while the Puppet is Broadside and Facing

Fish

Tail beating

Pelvic fin flickering puppet broadside facing

puppet facing broadside

Tail flashing puppet broadside facing

1

49·1

46·8

29·8

38·9

21 ·1

14·4

2

57·7

62·8

19·0

21-1

23·3

16·1

3

41·6

36·4

28·2

29·6

30·2

34·1

4

61·2

65·3

22-6

23·2

16·2

11·5

s

51-8

54·5

22·8

26·8

25-4

18-7

6

43-8

38·2

23-8

26·5

32·4

35-4

7

48·8

53·2

13-4

15·0

37·8

31 ·8

8

31·0

30·0

20·8

26·6

48·2

43·5

9

15·8

13·1

24·4

23·2

59·8

63·7

10

28·4

32·2

29·5

31·0

42-1

36·8

11

18·0

19·8

40·5

34·5

41·5

45·7

12

37·0

22'3

14·3

12·6

48·7

65·0

13

27'6

25·7

24·5

12·2

47·9

62·2

14

24·4

27·3

32-6

20·0

43·0

52'7

15

8·1

9·9

18-7

24'8

73·2

65'3

pelvic fin :flickering is positively correlated (rS = + 0·72, P < 0·01 to 0·001). Table XVI shows that tail beating contributes a relatively fixed proportion to the total. Thus pelvic fin flickering, as a proportion of the broadside display components, emerges as another measure of the fishes' approach readiness. Intuitively, an aspect of display which can be measured by the frequency of occurrence of two movements (fin flickering and tail flashing) relative to each other seems a more effective signal than the frequency of either relative to the broadside bout as a whole. Pelvic fin flickering and tail flashing are negatively correlated with each other (rS = - 0·67). This inverse correlation is not a trivial consequence of there being a limited amount of time available for broadside display movements during the broadside bouts (pp. 16 and 17).

The differential effects of the puppet's two orientations. The analyses in this chapter have

so far used only the variation between the differ­ ent individual fish. However, it was suggested in the introduction that the different orientations of the puppet might produce different behaviour patterns in the fish, perhaps making them spend less time near the puppet when it was facing. With such within-fish variation might be cor­ related other aspects of the display's variation, such as the frequency of tail flashing per broad­ side bout. In some respects, the fish change their be­ haviour little, compared with the variation from fish to fish, when the puppet changes its orien­ tation, as the tables in this chapter show. Thus tail beating per broadside bout while the puppet is facing is well correlated with tail beating per broadside bout while the puppet is broadside

53

VARIATION IN THE DISPLAY FROM INDIVIDUAL TO INDIVIDUAL

in the individual fish (rS = + 0·91), and these measures of tail flashing for the two orientations of the puppet are also well correlated (rS = + 0·93), but those for pelvic fin flickering less well (rS = + 0·52). Nevertheless, the puppet's orientation makes a difference to some of the display measures. Most fish that spend relatively little time near the puppet in the test as a whole, spend an even smaller proportion of the time near when the puppet is facing, while those fish spending most of their time near spend an even greater proportion of their time near while the puppet is facing. In other words, those fish that were relatively ready to approach the puppet in the first place, as they show by being near it for longer than might be expected by chance (Table XII), become even more ready to approach it when it shows more 'aggression' by turning to face. In terms of the data, the fish can be classi­ fied as 'approachers' or 'avoiders', depending on whether they spend more or less of their time near the puppet than would be expected by chance, given the relative volumes of their tanks, occupied by space 'near' and 'away' from the puppet*. Of the six 'approachers', four had their gill covers erect for more of the time while the puppet was facing than while it was broadside (Table XII), and of the ten 'avoiders' only two had their gill covers erect for more of the time while the puppet was facing. Moreover, five of six 'approachers' faced the puppet more frequent­ ly while it was facing, while only one of ten avoiders did so. The two orientations of the puppet might be expected to affect the frequencies of the broad~ side components of the fishes' displays. Although ten of fifteen fish (fifteen fish, because Fish 16 has been excluded for not making any broadside movements) beat their tails more frequently when the puppet was facing, eleven of fifteen flashed their tails more. Neither of these differ­ *Note that the actual movements of the fish in their tanks had not been observed before the test was started. It may well be that they avoided the wall of the tank close to which the puppet was to be put, because it was a front wall.

Table XVII Turning to Face while Puppet Faces ) _ 100, ( Turning to Face while Puppet Broadside x 100 and

Tail Beats while Puppet Faces x ) _ 100 100 ( Tail Beats while Puppet Broadside Turning to

Fish

face

Tail beating

+

+

15

44

2

243

73

3

139

147 13

4 5

15

12 46

25

6

5

7

24

45

8

12

41 13

9

10

12

50

7

11

43

25

12

22

41

13

26

62

14

74

61

15

28

19

ences is significant by two-tailed Wilcoxon matched-pairs signed-ranks tests. Tables XIV and XV show that these differences are rather small in most of the fish. While the puppet's orientation had rather little effect on tail beats per facing-broadside cycle (Table XIV), its effect on tail beating per unit time is greater, because the puppet's orien­ tation affects the rate at which the fish go through the facing-broadside cycle. For example, Fish 8 beat his tail 55 times while the puppet was facing and 39 times while it was broadside, while Fish 10 beat his tail 27 times while the puppet was facing, and 52 times while it was broadside.

54

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

In Table XVII the fish are scaled according to their scores of number of turns to face while the puppet is facing number of turns to face while the puppet x 100 is broadside and number of tail beats while the puppet is facing x 100 number of tail beats while the puppet is broadside respectively. Thus the dichotomous classification of fish into 'approachers' and 'avoiders' can be replaced by a continuous scale. The differential facing rate is positively correlated with the original scale of readiness to approach-the proportion of the whole watch that the fish spent near the puppet (rS = + 0·77, P < 0·001), and so is the differential tail beating rate (rS = + 0·74, P < 0·01 to 0·001). Figure 17 plots individual fish in terms of the differential effect

of the puppet's orientation (ordinate) and the proportion of the test spent with the gill covers erect (abscissa, with logarithmic scale). -----·~J!:+J_

80

•

60 40

•

20 0 - 20 -40 -60 . 17 ( F~ .

• • • •

80 60 40

•

• 20

•

4

10

•

•

• •

••

Tail beats while puppet faces ) x 100 Tail beats while puppet is broadside - 100 (ordinate) against the percentage of the time spent during the test with the gill covers erect (abscissa).

8. SUMMARY AND DISCUSSION OF RESULTS In this chapter the findings of the previous chapters are summarized and reconsidered in an attempt to build them into a coherent account of the relationships between events during the fishes' displays, and the outcomes of the dis­ plays. Finally, the processes that may underlie such relationships are discussed. A display can be described in terms of the alternation of the facing and broadside orien­ tations of the participating fish. When they are broadside, the fish may flicker their pelvic fins, beat their tails and flash their tails. The act of gill cover erection often coincides with that of turning to face, and the gills are often lowered when the fish turns broadside. Sometimes the gill covers are held erect all the while. The be­ haviour of the fish when they are carouselling (i.e. displaying parallel to each other, but with the head of one opposite the other's tail) and when they are biting each other, is excluded, from the accounts of the interaction that follow. Chapter 4 described a method of making generalizations about how some of the units in one fish's display follow each other. It showed that after a fish had turned broadside, pelvic fin flickering was the most likely movement early in the broadside bout, then tail beating became most likely, and finally tail flashing, often just before the fish turned to face again. Chapter 5 used the same methods of analysis as chapter 4, but applied them to the relations between the events in the displays of two inter­ acting fish. Using males on the two sides of transparent Perspex screens, it showed that a facing fish is more likely to turn broadside if its partner is facing than if the partner is broadside. It is also more likely to tum broadside just after the partner has turned to face than just after the partner has turned broadside. Some broadside fish are more likely to tum to face when their partners have just turned broadside. The males on their two sides of the Perspex screen spend much of their time in the mutual orientations

facing-broadside, someofit broadside-broadside, and least time facing-facing. When females have complete access to each other, they behave similarly, except that they spend more time mutually broadside. Chapter 5 also showed that in the pairs of males on the opposite sides of the Perspex screen, each turned to face approxi­ mately as often as its partner, and the two tended to face each other in turn. The last finding could not have been predicted from the data about the effects of each fish's orientation on that of the other. The data about the interaction of one fish's gill cover erection, and its partner's broadside display, come from analyses of pairs of females displaying with complete access to each other. (It is assumed that gill cover erections coincide with facing bouts). If a fish flickers its pelvic fin after its partner has raised its gill covers, it is most likely to do it in the first 1·5 sec interval after the partner has done so. There was no relation between the moment when the partner lowered its gill covers and when the fish flickered its pelvic fin. It is more difficult to generalize about the effects of gill cover erection on the partner's tail beating. But, whether the gill covers are raised or lowered, such a change in their position seems to be followed by a decrease in the part­ ner's tail beating frequency in the first l ·5 sec interval afterwards. In some fish, the frequency of tail beating then increases over the time that the gill covers are held erect. There may also be a temporal relation between the peak in the part­ ner's tail beating frequency, and the moment when the fish lowers its gill covers again. A possible interpretation of these temporal relations is that the tail beating fish, in each of the part­ ner's gill cover raising bouts, responds with an increase in tail beating frequency to the time the partner holds it gill covers erect. Finally the partner responds to the fish's tail beating by lowering its gill covers, and some partners may 55

56

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

be more responsive in this respect than others. When both fish are broadside, there is sometimes an increase in the tail beating of both, until one of them raises its gill covers. In comparing the displays of winners- and of losers-to-be, in encounters between females that have not displayed at each other before, chapter 5 shows that winners-to-be eventually spend a greater part of the time with their gill covers erect than do losers-to-be, although both increase in this measure in the course of display. Since the rate of raising the gill covers does not increase, the bout lengths of the gill cover erec­ tions must increase. The eventual differences be­ tween the winners and losers in the lengths of their gill raising bouts could be a consequence of different concurrent behaviour patterns by their partners, affecting the duration of the gill raising bouts, and/or different responsiveness in the fish, in lowering their gill covers in the presence of their partners. Since a fish is usually broadside while its partner has its gill covers erect, the effect a facing partner with erect gill covers has on the fish's broadside behaviour is interesting, and this is considered both in chapter 6 and in the next chapter. In chapter 6, attention is confined to the tail beating during the partner's gill cover erections. (It is likely that pelvic fin flickering is as import­ ant in some of the subjects shown in Table IX). But the effects of pelvic fin flickering were not analysed.) Table X demonstrates that when win­ ners and losers were compared for the frequencies with which they beat their tails while their part­ ners had their gill covers erect, the losers beat their tails more frequently in seven of the eight pairs. Comparison between the losers and win­ ners showed that the losers' tail beating rates per 2-min period spent by the partner with its gill covers erect were less, the longer the partner held its gill covers erect, while the winners' tail beating rates may even have increased the longer their partners held their gill covers erect (Fig. 14). These findings suggest that although losers' tail beating rates may have been slightly higher than those of the winners, the losers' tail beating had

less effect on their partners' gill lowering than did the winners' tail beating. Chapter 6 described a free-running situation where one fish's broadside display may have re­ flected the other's gill raising behaviour, and thus made it impossible to disentangle the con­ tributions of the fish and its partner to the fish's own display. Chapter 7 used a situation where different domestic male fish were allowed to display to a stationary puppet that changed its orientation every 2 min and showed that much of the variation in these fish's displays was orderly. (Note the limitations of this test situation. The puppet changed orientation every 2 min, and it did not give any display while it was broad­ side. Thus there are insufficient data for com­ parisons between the different fish for the effects of changes in the puppet's orientations, and it is not possible to compare the effect of a standard broadside display on the gill lowering and rais­ ing behaviour of the fish.) The fish could be said to vary in their readiness to approach the puppet, or their aggression towards it. Thus, with the proportion of the test spent near the puppet was correlated the proportion of the test spent with the gill covers erect, and with this measure were correlated total fin flickers (a) total fin flickers+tail beats + tail flashes, positively; and total tail flashes (b) total fin flickers + tail beats + tail flashes, negatively. (c) Also correlated with the proportion of the test spent with the gill covers erect was the measure of the fishes' responsiveness to the difference between the puppet's two orientations: total tail beats while the puppet was facing 1 total tail beats while the puppet was x OO broadside Displays are often described as if they reflected both tendencies to attack and to flee, but a failure to find an independent fear or fleeing 'dimension' among these display measures sug­ gests that such an hypothesis is unnecessarily

SUMMARY AND DISCUSSION OF RESULTS

complicated for Betta's display. Such hypotheses are discussed in chapter 9. At :first glance the :findings of this chapter, that :fish that beat their tails more frequently when the puppet turns to face are also those that have their gill covers erect for longer, seems to contradict the finding in the previous chapter, that the winning :fish, which have their gill covers erect longest, are those that beat their tails less when their partners have their gill covers erect. However, the two situations are not really com­ parable, because the fish's tail beating can affect the partner's gill cover erecting and lowering in the fish-fish situation, while it cannot affect the puppet's orientation.

Discussion Any speculation about how the display enables the :fish to resolve their encounters will obviously depend upon fragmentary data about part of the display only. However, such speculation may suggest further analysis and experiments, and some of these may highlight processes involved in the display. During an encounter, there are two sorts of change to be looked for: the parallel changes over its duration in both the fish, such as the gradual increase in the durations of their gill cover erections, and the differences between the two that emerge with time, as when one of the fish outstrips the other in the durations of its gill cover raising bouts. Braddock & Braddock (1955), Laudien (1965) and Clayton & Hinde (in press) have data about the manner in which the display changes with time spent displaying. Braddock & Braddock found that female fish, which had been isolated for 7 days before they were allowed to display with each other, did not usually start to bite before the third 2-min period displaying together, and the mean number of minutes before the first rapid exchange of bites was 6·6. Even in long fights, the highest biting rate seldom occurred before the 15th min. Laudien and Clayton presented males with mirrors, and they offer data about the display changes during the first 12 and 26 min of such displays respectively.

57

In two subjects, Clayton shows an increase in tail beating and rate of gill cover erection during the watch, with gill cover erection rate reaching its peak first. Laudien's two :figures show the same finding, except that his fish were quicker to reach their peaks in these measures. Laudien's fish then started to bite the mirror, both reaching a peak by the 9th min. In contrast only two of thirty fish, used by Clayton, ever bit in their first 26 min with mirrors. Simpson (1966) com­ pared the change in the tail beating and biting per facing-broadside bout in two fish on their first exposures to mirrors, and found that in the fish that beat its tail and did not bite, tail beating per broadside bout reached its peak in the fifth 5-min period. In the other fish, that bit as well as beating its tail, tail beating had reached a smaller peak earlier, and biting per facing bout reached its peak in about the fifth 5-min period. The mirror findings all show that, even in a situation which is constant, in the sense that the mirror does nothing that the fish has not done first, the display becomes more violent in terms of rate of gill cover erection (which is correlated with the rate of going through the facing­ broadside cycle, chapter 6) and in tail beating and biting. The latter increase is a consequence of an increased rate of going through the facing­ broadside cycle, and of an increase in frequency per cycle (Simpson, 1966). The mirror experi­ ments also show how great the variation in the course of the response is from fish to fish. The parallel changes in the displays of two fish displaying at each other could be the simple consequence of an increase in the violence of display with time, independently of moment to moment stimulation. But if there is some re­ lation between the two fishes' facing-broadside cycles, so that they can face each other at equal rates, it is likely that the fish will keep 'in step' in respect of these changes. Moreover, when two fish are broadside and one beats its tail violently, the other does so too, and when one bites, the other often bites back. Figure 13 shows that the in­ crease in two fishes' time per 2-min period spent with their gill covers erect can be very similar

58

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

from one 2-min period to the next. Only towards the end do the fish diverge in this measure. In order to discuss possible processes occur­ ring during displays between pairs of fish, a simple and ideal account of the changes in the display will be used as a starting point. At first the fish parallel each other in the bout lengths of their gill raising bouts; then one of them out­ strips the other in this aspect of its display; and then the other fish soon stops displaying. By what processes could these events be connected? The ideal display sequence where the fish take it in turns to raise their gill covers at each other, and where the gill raising bout of one fish hardly ever starts before that of the other has ended, will be considered. How does one fish 'match' an increase in the duration of its partner's gill cover erection with an increase in the duration of its own? Each fish may be responding, by altering its subsequent readiness to lower its gill covers, to the duration of its partner's gill raising bout, and perhaps also to how the partner has re­ sponded, by lowering its gill covers, to the fish's broadside bout. For example, if the partner originally lowered its gill covers in response to one tail beat by the fish, but if now the fish has to beat its tail twice before the partner lowers its gill covers, the fish itself may become cor­ respondingly less responsive to the partner in terms of the time when it lowers its own gill covers in the presence of its partner's display. At the end of the display, one of the fish finally continues to increase the durations of its gill raising bouts, in spite of further increases in the other's broadside display, and the other 'gives up' when it can no longer control the partner's gill cover erections. (Alternatively, the other fish starts to bite, but encounters which are de­ cided in terms of biting have not been considered in this monograph.) If the foregoing interpretation is correct, then it suggests an ability of one of the fish to respond to aspects of the timing of its partner's display relative to its own display. Two observa­ tions, each of a single fish, suggest how such a suggestion could be followed up.

The first observation uses the one-way mirror situation. If the fish on the bright side stays near its mirror image, some of its facing and gill raising bouts become long, relative to those of the fish on the dull side, so that the latter may go through three facing-broadside cycles to one 20-sec facing bout of the former. Moreover, the latter can see the former, but its display cannot affect these long facing bouts, because the fish on the bright side cannot see past its reflection (see also chapter 5). Figure 18 shows the tail beating behaviour of one fish displaying on the dull side of a one-way mirror, and compares tail beating in the first and third broadside bouts after the partner turned to face, on the twenty-five occa­ sions when the partner faced long enough for the fish to turn broadside three times running. It can be seen that the fish on the dull side beats its tail more frequently during its third broadside bouts in the presence of a facing fish than it did in its first broadside bout, as if it is able to re­ spond to the time spent facing by its partner, and/ or the number of broadside bouts it has gone

gi040

~

..0

~

020

I

\ I

1/

I

P,

'-

'o,

I

'-

0

15

30

60

'-

0

I

I

I

90

Seconds

Fig. 18. Tail beating per 1·5-sec interval (ordinate) in the successive intervals (abscissa) after the fish had turned broadside for the first time (filled circles) and third time (open circles) after the partner had turned to face (see text).

SUMMARY AND DISCUSSION OF RESULTS

through since its partner turned to face, and/or the number of times its partner failed to respond to such broadsides of tail beats. One interpretation of the preceding result is that tail beating in the fish has the goal of lower­ ing the partner's gill covers and of ending its facing bout, and the longer the partner stays facing, the more the fish beats its tail, in an attempt to achieve such a goal. One definition of goal-directed behaviour is that present be­ haviour is adjusted to reduce discrepancies be­ tween the existing situation (e.g. partner facing) and the goal situation (e.g. partner broadside). Such behaviour is also often characterized (e.g. Thorpe, 1963) as having rather a constant end­ point (e.g. eggs in a male stickleback's nest) and many possible starting points (e.g. where the male might find females). But unless the relevant variables can be isolated and measured (e.g. Mittelstaedt, 1964), the idea of goal direction as applied to behaviour is merely a suggestive metaphor. However, the following observation (details in Simpson, 1966) was part of an attempt to give a fish an opportunity to stop the puppet facing by beating its tail, in one condition, and by turning to face itself, in the other condition. It may be argued that if the fish controls the puppet's facing behaviour in the same way by these two different methods, then such facing behaviour by the puppet is one goal of the fish's display. It was expected that the fish would turn to face, or beat its tail, as soon as possible, thus keeping the puppet's facing bouts as short as possible. In the experimental trials the puppet turned to face independently of the fish, but only turned broadside after the fish had beaten its tail, or turned to face itself. (The observer controlled the puppet's behaviour through two of the keys on the event-recorder on which the fish's behaviour was being recorded.) In the control trial, the puppet turned broadside 5 sec after it had turned to face, regardless of what the fish had done. The results suggested that the fish preferred not minimum bout lengths of facing by the pup­ pet, but facing bout lengths of a particular

59

length, about 5 sec. The fish grouped the re­ sponse (tail beating or facing) at this time, and when the puppet's turning broadside was con­ tingent upon tail beating by the fish, the fish delayed its tail beating compared with the other situations, where tail beating occurred before 5 sec had elapsed after the puppet turned to face. If one goal of the fish's display was facing bouts of a particular length by the puppet, then the fish must be able to respond to the duration of the puppet's facing bouts. The point of view of the display that is being developed can be described as an Sl-R-S2 view, similar to that of Teuber (1961), Held & Hein (1963), Miller et al. (1960) and reviewed by Hinde (1966). Thus, during display the partner may be facing (SI), the fish may beat its tail twice (R), and the partner may or may not re­ spond (S2) by turning broadside. Depending on S2, the fish will alter its further behaviour. In this account of the display, S2 includes aspects of the display's timing. If the delay after the fish's two tail beats and before the partner lowers its gill covers is long, then the next time the fish has its gill covers erect, the partner may beat its tail three times. If this delay is very long, the fish may stop to display altogether, or it may start to bite its partner. The ability of animals to respond to the timing of events has been widely demonstrated. Thus pigeons can be trained to peck a key for a reward after a delay of more than 20 sec since after they last pecked it (Kelle­ her et al. (1959). Sokolov (1960) has found that after a human being has been repeatedly pre­ sented with a light stimulus of a particular duration, the 'orientation reaction' wanes, but reappears if the stimulus duration is changed. Thus, if the stimulus is prolonged, the reaction reappears for the time that the new stimulus overlaps the original one, and if it is shortened, it reappears for the time that the old stimulus would have continued beyond the end of the new one. In the introduction to this monograph, the question of whether the effects of a change in the partner's display extend beyond the next

60

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BE1TA SPLENDENS

move by the fish, was raised. It could be argued that, since the display has the function of resol­ ving a dominance-subordination relationship between two fish, all events in it affect its out­ come, and so even the first events during the display may be affecting the occurrence of events 5 or 10 min later, at the very end of the encoun­ ter. But need such connections between these widely separated events involve the mechanisms in the fishes' C.N.S.s, concerned with integrating their whole experience of their displays, in coming to a final 'decision' about whether to stop or not? Prolonged human activities, such as games of draughts, or bidding at auctions, can be carried to their outcomes without the par­

ticipants 'remembering' more of their preceding moves than is sufficient to tell them whether their turn has come or not. Likewise, a displaying fighting fish must 'decide' when its turn (to beat its tail, or to raise its gill covers) has come, whether its partner's response warrants a change in its own future display, or the cessation of its display. In this chapter, it has already been suggested that, in making these 'decisions', a fish needs to draw on its experience of the partner's response during its previous facing-broadside cycle, and experiments such as the ones described in this chapter may provide evidence about which aspects of the partner's response are relevant.

9. REVIEW OF METHODS FOR STUDYING DISPLAYS preliminary guidelines may be provided by temporal correlations between the displays of the two participants, and within the displays of the individuals. Thus, an increase in the fre­ quency with which one fish beats its tail may be followed by an increase in the chance that its partner will lower its gill covers, and the subject that holds its gill covers erect for the greater proportion of the time at the end of the en­ counter may become the winner. Such findings suggested that the interaction of tail beating and gill cover raising and lowering was a promis­ ing one for detailed study. In such preliminary studies of free-running interactions it is necessary to be able to identify the two individuals during the encounter, and to record as much of the behaviour of both as possible, so that differences between them can be sought. More special and detailed studies can then follow. The problem of the relation between the inter­ action during an encounter and the final out­ come is a widespread one, because most en­ counters involving interaction between the par­ ticipants have more than one outcome. Thus, when a female is placed in the tank of a nesting male, the ensuing 'courtship' interactions do not necessarily go as far as the laying and fertili­ zation ofeggs. At first there is almost always some chasing and ramming of the female by the male, and the encounter may end at this stage, with the female remaining out of sight. Even if the court­ ship is consummated, its duration differs from pair to pair, and this duration may depend on the preceding interaction. (See Kiihme's 1963 description of Betta courtship.) Tinbergen (1959) was aware of this problem in courtship behaviour when he suggested that a major function of the early stages of the interaction was the reduction of aggression of the participants. Hinde (1953) described the progressive increase in a male chaffinch's fear of the female during courtship; such a change may depend on the preceding interaction. Levine, Barsel & Diakow (1966) attempt to interpret the greater mating success

In few fields of biological study is it so easy to obtain results and so difficult to explain them as it is in the study of animal behaviour. Con­ sequently, many experiments in this field seem to be done merely because they are possible, and the interpretations seem to become more summary as the experiments proliferate. This monograph has added more methods to the long list. Can the methods it describes be used for other studies, and can the results be discussed in wider terms? This chapter describes the ad­ vantages of the methods used in this monograph for any study of interaction. It then discusses interpretations of display behaviour and the possibilities of testing such interpretations. Finally, some problems raised by recent work with Siamese fighting fish are reviewed, to emphasize that although this monograph raises questions and suggests way of answering them, it does not succeed in providing a definitive description of the threat display. Methods for the Study of Interactions It is easy enough to describe and list the moves in an animal's threat or courtship behaviour, and particular aspects of the display can be selected for detailed study on the basis of the ease with which they can be recorded. But it is not so easy to understand an interaction in terms of the relationships between the events during the interaction and its final outcome, although this is an urgent and inviting problem. Difficulties in interpretation may arise, because the interaction may last for a considerable period, so that events widely separated in time may nevertheless participate in a causal pattern, and the complexity and time scale of such a pattern will have implications for theories about the nervous mechanisms underlying it. It is so difficult to break the stream of be­ haviour into parts still bearing a meaningful relation to the whole that selection of particular parts for detailed study all too easily becomes a random 'botanizing among reflexes'. However, 61

62

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

(proportion of matings that are fertile) of ST/J mice over CBA/J mice, and they find that ST/J males make the most mounts and fewest thrusts per mating encounter. On a longer time scale, Spencer-Booth, Hinde & Bruce (1966) describe how the development of infant rhesus monkeys' behaviour can be influenced by the restrictive­ ness of their mothers. Ethological Interpretations of Display This monograph has been concerned with the differences between the displays of individuals, and the differences in an individual's display from time to time, rather than with the question of why the display occurs in the first place. Many studies (reviewed by Hinde, 1966) have been of animals in situations where they may attack or flee, as well as display. Such studies raise the question of why the animal sometimes displays rather than attacks or flees. Questions about the relationships between particular frequencies of attack and flight (Stokes, 1962a) or particular frequencies of wins and losses (Kruijt, 1964), and the accompanying displays may also be raised. Studies of displacement activities (re­ viewed by McFarland, 1966a and 1966b, and Hinde, 1966) raise analogous questions. For example, Iersel & Bol (1958) study the situation where a tern preens after landing near its nest, rather than walking toward the nest, or flying away again. lf an animal attacks, flees and displays several times during the period in which it is watched, then its behaviour may be described in terms of its attacking and fleeing frequencies, sometimes also called its attacking and fleeing tendencies (e.g. Hinde, 1955/6 and 1966). In examining the results from several such periods, we may find the periods with most display to be those in which the frequencies of attacking and fleeing are most closely balanced. A common inference from such a result is that the conflict between the animal's tendencies to attack and to flee causes the display. In making such an inference, the tendencies are raised from their empirical status to the status of such logical constructs

as hunger or fear drives, for the conflict must be between two (or more) entities. There is another way in which the term 'tendency' can depart from its 'operational' meaning. In this monograph, factors influencing the display have been considered one by one, although many factors must in reality be influ­ encing the display simultaneously, and their combined effects may not be the ones expected from their separate effects. (This is a matter for empirical research.) However, it has often been pointed out (e.g. Tinbergen, 1959) that the situ­ ation in which the animal displays often com­ bines aspects some of which would, by them­ selves, cause flight, others attack, and others mating in some situations. The animal's tenden­ cies may be inferred from the situation in which it displays, as well as from the overt attacking, fleeing and mating behaviour accompanying its display. In field studies of displays (e.g. Moyni­ han, 1962) the values of the tendencies are inferred after the event. Sometimes, however, the event can be arranged. Blurton-Jones'(l958-9) Canada geese usually pecked strangers, and beat them with their wings. If Blurton-Jones dressed as a 'stranger' (i.e. wore strange clothes) they would attack him unless he carried the broom with which they were driven to bed every night. Then they neither attacked nor fled (as they would if Blurton-Jones wielded the broom when wearing his everyday clothes), but displayed in­ stead. But whether the situation is interpreted after the event, or arranged before it, to argue that the displaying animal analyses its situation in the same way as does the ethologist, is to assume that the animal attends to certain of the welter of possible stimuli, and that it classifies them in certain ways, i.e. into those promoting attack, flight etc. To show that an animal has been attending to a stimulus to which it was not responding by overt behaviour requires quite subtle research. McFarland's (1966b) paper, reviewing displacement behaviour with refer­ ence to reversal learning situations, contains some hints. Until such work has been done, the dangers of relating the animal's situation to the

REVIEW OF METHODS FOR STUDYING DISPLAYS

attack tendencies etc., are the dangers of any unitary drive concept (reviewed by Hinde, 1959) with its implication that some factors in the situation are equivalent in their effects, and others ineffective, for each of the two or three separate drives*. Having referred to some of the dangers of the conflict approach to display, it remains to be shown how usefully it suggests ways in which the display can vary, and in which it can be related to the observed attacking and fleeing behaviour. The preceding section showed how the pattern of display can be related to approaching and fleeing behaviour. To show this, the frequencies of attacking and fleeing (or some other measures of non-display behaviour) must be measured independently, and different forms of display must be distinguished. Sometimes display can be described along a continuous scale (e.g. fre­ quency of tail flashing relative to the total broad­ side movements in this monograph, distance between front and hind legs in Leyhausen's (1956) catst). Sometimes different forms of display can be ranged according to the animal's actual or presumed attacking and fleeing be­ haviour. Examples include the tail kinking in Leyhausen's (1956) diagram of cat displays, where aggression is high, and fear moderate; and the different gull calls in Moynihan (1962) for particular absolute and relative values of attacking and fleeing. Note that in both these papers, the procedure for evaluating the attack­ ing and fleeing probabilities of the animals is not explicit. If there are several measures of display, it may be possible to test whether the display need be described in terms of more than one 'dimen­ •Tue contributions of tendencies to attack, flee etc. may also be argued from the forms of the display move­ ments (Tinbergen, 1959). In the 'aggressive upright' movement, are components of the pecking down of attacking gulls (Tinbergen, 1959). See Blest (1961) for discussion of the ritualization of display movements, and note that movements associated with locomotion need not be the only ones ritualized in evolution. Al­ though pelvic fin flickering in Betta splendens has components in common with pelvic fin movements in starting and stopping, it also resembles the scissoring movements by which the fish cut off strings of faeces. f Picture also in Hinde, 1966.

63

sion'. For example, the distance between the fore and hind feet of a cat seems to vary in­ dependently of how upright that cat stands (Leyhausen, 1956), and the distance between fore and hind feet may be an inverse measure of fear, while the degree of erectness with which the cat stands may be a measure of its aggression. In contrast, most of the measures of Siamese fighting fish display studied here seem to be cor­ related, suggesting that it varies only with the fish's probability of approaching. If the sole function of the fighting fish display is to establish dominance-subordinate relations, then it would be sufficient for the participants' displays to vary along one dimension only. If the two are very different in size, then the out­ come can be decided in terms of their actual lengths, as seems to be the case in domesticated female fighting fish that display for long periods of time (Braddock & Braddock, 1955), in Tilapia mossambica (Neil, 1964), and in the colour fights between Badis badis males (Barlow, 1963). Chapter 7 in this monograph showed that many of the measures of the display varied along one dimension only, so that given one measure of it, many of the other measures could then be calculated. From chapter 6 can be seen how one of this cluster of measures, the proportion of the time spent with the gill covers erect, was cor­ related with success in an encounter. If the display varies along one dimension only, and if outcomes of encounters can be resolved in terms of differences along that one dimension, then a conflict model would seem to be superfluous. Displays are seldom so simplet. While some measures of an animal's display can be ranged along continuous scales, certain movements occur only when the continuous scales have certain values. Thus, if some of the fish described in chapter 7 had bit the wall of the tank nearest the puppet, they would have been at the top of the scale of gill cover erection, pelvic fin flicker­ ing etc. Moreover, if the animals are scaled in tSee also Willis' (1967) comparison of such simple dis­ plays which have been described with reference to conflict models.

64

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

terms of the frequencies of approaches and flights before and after their encounters, then particular movements may occur at particular positions along such scales. Thus Stokes (1962a) sha shown that a blue tit that raises its crest never attacks, but flees subsequently on 90 per cent of the occasions, while the probability of fleeing is never so great after other display move­ ments. Wiepkema (1961) interprets the occur­ rence of fin spreading, jerking and turning beats in bitterlings in terms of the ratios of attacking and fleeing tendencies caused by the size of the opponent relative to the fish (i.e. when the fish has an opponent larger than itself, its fleeing tendency was presumed to be greater than its attacking tendency). Wiepkema's case, where certain display move­ ments are most frequent when there is a particu­ lar ratio between the animal's attacking and fleeing tendencies, is also a case where the movements are most probable when there is most conflict, in the sense that the tendencies* are balanced. This approach would suggest many further ways of analysing Betta splendens' display, if the fishs' approaching and fleeing frequencies could be measured independently of each other. Un­ fortunately, the measure used in chapter 7, 'proportion of the time spent near the puppet', provides a measure of approaching behaviour only. More detailed analyses of visiting and leaving could provide separate measures. For example, the leaving behaviour could be meas­ ured in terms of frequency of leaving per 10 sec spent near the puppet, and the approaching behaviour in terms of the frequency of approach­ ing per 10 sec spent away from the puppet, and these measures could vary independently of each other. Thus some subjects might make short visits, and spend short periods of time away (high leaving and high approaching tendencies*), while others might make short visits, but spend long periods of time away (high leaving and low approaching tendencies*) etc. Preliminary an­ •Is used whenever the term tendency is meant to describe a drive-like entity.

alyses, however, suggested that the fishes' be­ haviour was simpler, in that if they spent any time away from the puppet (or away from a mirror to which they displayed) they approached it at regular intervals (e.g. of approximately 40 sec), or sometimes at multiples of the interval (e.g. some of the approaches would be separ­ ated by about 80 sec), so that the longer the time they remained near the puppet after an approach, the shorter the time they spent away before returning again, i.e. the suggested meas­ ures of approaching and leaving tendencies* would not vary independently of each other. A complete account of the temporal pattern of the visiting and leaving, which takes into account the variation from fish to fish, has yet to be made. In analysing the data from chapter 7, it is nevertheless tempting to suggest that those fish intermediate in the scale of approaching the puppet, and raising their gill covers at it, are also the ones in greatest conflict. To do this, it must be assumed that the fear tendency* is the same in all fish (caused by the puppet, which is the same for them all). It must be further assumed that in those fish at the top of the scale (of approaching etc.) the approach tendency* exceeds the fear tendency*, while in those at the bottom of the scale, the approach tendency* is less than the fear tendency*. Supporting this assumption is the finding that the former spend more time near the puppet than would be ex­ pected by chance (Table XII), while the latter spend less time near it than would be expected by chance, and the former beat their tails more frequently when the puppet faces, while the latter do so less frequently. Tables XIV and XV show that the measures of display intensity, tail beating and tail flashing per broadside bout, tended to be greatest in fish that were inter­ mediate in terms of the proportion of the time spent near the puppet, and the proportion of the test spent with their gill covers erect. These intermediate fish were also those that beat their tails at about the same frequency whether the puppet was facing or broadside, and it could be argued from this that these fish were in greatest

REVIEW OF METHODS FOR STUDYING DISPLAYS

( 147•)

------­

100 80

•

60

-

•

40

•

20

•

0 0-3

Q.5

lO

•

• •• •

• 20

JO

• 6-0

• 8-0

. 19 ( tail beats while puppet faces x 100) Fig. · tail beats while puppet is broadside - 100 (ordinate) against tail flashes per broadside bout (abscissa). See footnote on p. 64.

conflict about approaching or leaving the puppet. Figure 19 shows that the more a fish flashes its tail per broadside bout, the smaller is the difference t made to its overall tail beating frequency by a change in the puppet's orienta­ tion. In other words, tail flashing per broadside bout could be a measure of the fish's conflict. Conclusion. The idea of conflict can be a convenient metaphor to guide one approach (of many possible ones) to studying displays, especially their variation from time to time and from animal to animal. The idea reminds us that some aspects of the display may vary with fleeing behaviour, others with attacking behaviour, and still others with mating. But the apparent simplicity and completeness of statements about attacking and fleeing tendencies, and the conflict between them, may distort the processes by which initial descriptions of behaviour are made, and discourage systematic analysis of the factors that could influence display behaviour. Opportunities for Rearch into Betta splendens' Threat Display The preceding section reviewed interpretations of display that were originally applied by field workers to behaviour occurring in situations over which they had little control. Such inter­ tNote that in Fig. 19 the sign of this difference is dis­ regarded.

65

pretations concealed many assumptions which were discussed. This section discusses some cur­ rent problems posed by threat behaviour. The limited aim of this monograph was to produce a coherent account of the way in which two fighting fish establish a dominance-sub­ ordination relationship by displaying at each other. But this aim has not been achieved com­ pletely. Many inconsistencies between the results from the different methods of studying display remain. For example, two displaying males separated by a Perspex screen face each other an approximately equal number of times over a 5-min period (Table I), but when two pairs of females are allowed to display with complete access to each other, they do not always face each other an equal number of times (Table VI). But, when there is a large discrepancy in the number of times the two participants in such a female-female encounter face each other, one of the fish often faces the other almost exactly twice as often as the other. Such a finding, if repeated, would raise further questions about the coordination of the fishes' displays. When the picture of the variation in display from fish to fish in situations where the fish display at each other is compared with that in situations where different fish display to the same puppet, there are many respects in which it is impossible to reconcile the two. Thus the differences in the patterns of broadside display between more and less aggressive fish, as re­ vealed in the puppet experiment, do not appear in comparisons between more and less aggressive fish, as measured by the outcomes of their encounters with each other. Such difficulties may reflect in part the artificiality of the puppet situation, where the 'partner' holds the same orientation for 2 min at a time, and where it never responds to anything the fish does. Ob­ viously, a next step would be to use the fish in stranger-stranger encounters in 'round-robin' fashion, and to repeat the puppet experiment with these fish. In this monograph, the factors affecting the fishes' readiness to display in the first place, and

66

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

determining their particular patterns of display, have hardly been considered. Thus, although the procedure, described in chapter 7, for ensuring that most of the fish displayed to the puppet was effective, it is not understood. But this work does provide data about the relations between the various displays measures, which could guide the choice of measures in future studies. Studies of the effects of different treatments on the same individual could be extended in the light of the findings about the variation in display from in­ dividual to individual. (Note that the variation from fish to fish is such that each may have to be used as its own control.) Examples of studies that could provide starting points include Liss­ mann's (1933), one of the displays elicited by different two-dimensional models, Hess's (1952) on the effects of temperature on the display to a model, and Marrone, Pray & Bridges' (1966) on the effects of norepinephrine on the ease with which the display can be released. Such studies, if extended, could raise the question of whether the relations between the display measures found in the puppet situation obtain in all situations. Clayton & Hinde's (1968) study of the waning and recovery of display to a mirror image shows that during prolonged presentations certain relations (e.g. between biting and gill cover erection) change. The ways in which experience of displaying in situations with special feed-back relations changes the pattern of the display could reveal more about its mechanism. These studies are complicated by the fact that the displays of individuals differ so widely, and Laudien (1965) and Clayton & Hinde (1968) provide data for individual fish which demon­ strate how complicated such variation is. Their work, and that described in here, suggests that such studies must include at least three measures of the display, such as the proportion of the time spent with the gill covers erect, the rate of turning to face (which is also the rate of going through the facing-broadside cycle) and the rates of the different broadside movements per broadside bout.

Reinforcing Properties of Display

Recent studies (e.g. Thompson, 1963 and Thompson & Sturm, 1965a) show that oppor­ tunity to display is reinforcing for domesticated male Betta splendens. In other words, when a situation is so arranged that one consequence of a particular non-display act is a view of a display-eliciting stimulus, the fish come to re­ peat that act more often. The act may be swim­ ming through a hoop (Thompson, 1963), or swimming through a series of three doors (Thompson & Sturm, 1965a), or from one arm of a U-shaped runway to the other (Hogan, 1968; and the display-eliciting stimulus may be a view of the fish's mirror image (Thompson, 1963 and Hogan, 1968), a moving model (Thom­ son & Sturm, 1965a), a stationary model (Thompson, 1963), or the view of another fish through a Perspex screen (Simpson, 1966). Note that in none of these situations is it possible to distinguish the reinforcing effects of the sight of the display-eliciting stimulus from the reinfor­ cing effects of the act of displaying to that stimulus. So many classes of event in the lives of animals have so far been found to reinforce behaviour patterns leading to them (see Hinde, 1966 for a review*) that Premack (1959 and 1965) has raised the question of whether there are any events that can be shown not to be reinforcing. This is a challenging way of asking whether re­ inforcers can be considered to be a special class of events. Premack (1965) suggests that reinforce­ ment involves a relation, so that whether the opportunity to perform a certain response is re­ inforcing or not depends on the relative probabil­ ities of the response, and of the behaviour on which the opportunity to perform that response is contingent. These probabilities must be meas­ ured in unconstrained situations, and this makes it obvious that in practice it is difficult to com­ pare the probabilities of different responses meaningfully. Premack's hypothesis is illustrated by the following example. Thirsty rats will run *See also Stevenson (1967), Liley (1966) and Thompson (1964).

REVIEW OF METHODS FOR STUDYING DISPLAYS

more in a wheel if the opportunity to lick a water spout is contingent upon wheel-running, and they will lick at the water spout more (even when they are not thirsty) if the running wheel is unlock­ ed only after they have licked the water spout. In contrast to Premack (1965), Glickman & Schiff (1967) and Hogan (1968) hold that oppor­ tunities to perform some classes of responses are better reinforcers than opportunities to per­ form other classes of responses. The best re­ inforcers, according to this hypothesis, are con­ summatory responses, as defined by Lorenz (1935), and Schiller (1958). Hogan (1968) con­ trasts his consummatory response theory with Premack's (1959 and 1965) prepotent response theory. In Tinbergen (1951) the performance of a consummatory response ends a chain of pur­ posive behaviour, such as the courtship of a female stickleback by a male, when it is released by the special sign stimuli (such as the presence of the female in the nest) which the animal en­ counters as a result of its foregoing interaction with the environment. Because such chains of behaviour start more often than they are con­ summated, such final consummatory responses are unlikely to be 'prepotent' (i.e. relatively probable in Premack's sense), so that it should in principle be possible to disprove Premack's generalization by showing that opportunities to perform such responses were reinforcers that were effective out of proportion to their frequencies relative to the foregoing re­ sponses. This should at least be possible in cases where the consummatory response can be easily defined, as in sexual behaviour. In rat sexual behaviour, it has already been shown that the opportunity to perform incom­ plete chains is reinforcing for the males (Sheffield, Wulff & Backer, 1951; Kagan, 1955; and Whalen, 1961); and that being allowed to per­ form the complete chain (i.e. to ejaculate) is most reinforcing in the sense that it leads to the greatest number of correct turns in T-maze learning. But it is difficult to interpret this result in terms of the values, as reinforcers, of the separate acts in the chain mount, thrust, in­

67

tromission and ejaculation, when the later acts cannot be elicited without the former ones. In Betta splendens' threat display it is difficult to recognize any consummatory act in the par­ ticipants' displays, for the display ends when the loser merely ceases to display without there hav­ ing been any obvious preceding change in the winner's display; and the winner stops too, after spending a few moments displaying to a decreasingly responsive partner. In the situations used by Thompson (1963) and Hogan (1968) to study the reinforcing effects of the display, it has not been allowed to come to any such conclu­ sion, and the times when the fish have been able to see and display to the stimulus have been shorter than 20 sec. In these situations, the partner disappears, but without paling, or giving the fish on opportunity for a chase, and it reappears as soon as the fish repeats the act on which its reappearance is contingent. Such considerations suggest that the consummatory response theory will not be testable for Betta displays. Betta splendens' threat display nevertheless provided many opportunities for studying the properties of reinforcing events. For example, Hogan's (1968) factual objection against Pre­ mack's (1965) account of the situation is the finding that the fishes' improvement and ex­ tinction of their runway performance were qualitatively different from those for food. Although their overall swimming speed for display was less than that for food, swimming times during display training in the runway were much more variable than those in food training, and all fish swimming for display swam as fast or faster than they ever swam for food. Their extinction was also much more rapid than that for food. Thompson (1963) suggested that the situation most effective for releasing display was also likely to be the best reinforcer. Thus he found that 20-sec views of their mirror images main­ tained the highest response rates, followed by the 20-sec views of the moving model, followed by the 20-sec views of the stationary model.

68

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

Unfortunately, he gave no independent meas­ ures of the display in the 20-sec periods, but in Thompson & Sturm (1965a) one blue-green fish swam a maze most often to secure a 4-sec view of a red model, less often for a green one, and least for a blue one, and the percentages of the viewings when the fish also displayed were respectively 99, 95 and 92, in the first five sessions with each colour. Baenninger's (1966) result also supports Thompson's suggestion. He arranged a situation where a fish could visit, from a central compart­ ment, either a compartment where there was a view of a mirror, or on the other side a compart­ ment where there was a view of another fish, which did not display much because it had been habituated. The subjects of the experiment spent three times as long with their mirror images, in the presence of which they displayed more in­ tensely, than they did in the presence of the habituated fish. Nevertheless, they tended to alternate between the mirror and the fish (Baenninger, personal communication). The fact that the fish did not spend all their time with either of the display-eliciting situations suggests that their effectiveness as reinforcers may change from moment to moment. In the previous chapter it was suggested that certain responses by the partner, such as its act of turning broadside, may reinforce certain parts of the fish's display. If it could be confirmed that some display responses by the partner were more reinforcing then others, then develop­ mental studies would become interesting, since the question of whether these responses were always particularly reinforcing would follow. If so, it would then be interesting to see whether the normal development of the display de­ pended on the fish being able to interact with a fish. that responded with the reinforcing re­ sponses. In such studies, it would also be inter­ esting to see what part was played by classical conditioning. Studies of the effects of isolation of week-old fish on their adult displays show that the com­

ponent moves look the same (Braddock & Braddock, 1958 and Laudien, 1965), but that the fish do not display so intensely to their mirror images as do fish that have been brought up together (Laudien, 1965). It remains possible that the sequences and frequencies of the move­ ments in single fish, and their coordination in pairs of fish, may be affected by isolation. Shaw (1962), working with sexual behaviour in platy­ fish, found that the orientation of some of the display movements was adversely affected if the fish had been reared in isolation and pre­ vented from seeing beyond the walls of their tanks. In Betta, the development of the facing­ broadside cycle, and of its coordination in pairs of fish, is an obvious subject for developmental research, and the feed-back to developing fish from their displays could be controlled by pro­ viding them with mirrors only, or by ensuring that their only view of displays was of displays offish on the bright sides of the one-way mirrors, which their own displays could not affect. Thus studies of the development of Betta displays could follow the lines suggested by Hein & Held's (1962) and Held & Hein's (1963) sensory­ motor coordination studies. The emphasis of this discussion on the ways in which experience of interaction can modify patterns of display has been from an operant point of view. But classical conditioning could also play a part. Adult Betta splendens can be classically conditioned to raise their gill covers with a weak electric shock as a conditioned stimulus, and with a mirror as an unconditioned stimulus (Adler & Hogan, 1963). Thompson & Sturm (1965b) showed how fin erection, undu­ lating movements, gill cover erection and frontal approach were acquired as conditioned re­ sponses to a red light, presented before, and overlapping with, the presentation of a mirror. Such findings also suggest that Betta splendens' display will provide material for research on the question of differences between operants and respondents.

10. SUMMARY A display pattern which combines orientations lasting several seconds (e.g. broadside) with almost instantaneous movements (e.g. tail beating), is difficult to describe in a way that preserves information about its temporal pat­ tern. The fourth chapter develops a method of describing a behaviour pattern of several units of behaviour. The frequency with which each unit (e.g. pelvic fin flickering) occurs is given for the successive intervals after some reference event (e.g. turning broadside). Thus, in a population of broadside bouts, there may be pelvic fin flickering in 1!!0 of their first 1·5-sec intervals, but only in l'-o of their second intervals. A method for testing whether patterns revealed in such analyses (e.g. that pelvic fin flickering occurs mostly early in the broadside bouts) could have occurred by chance, and for testing the statistical significance of differences between patterns, is developed. Broadside bouts commonly have a few fin flickers in the 1st sec or so, two tail beats in the 3rd to 5th sec, and a tail fl.ash as the fish finally turns to face, after 4 or 5 sec. The fifth chapter extends this method of analysis to the interaction between two fish. Then the reference event is provided by some action of the partner, such as its act of raising its gill covers. The finding that two males separated from each other by a Perspex screen face each other at approximately the same rate, and tend to take it in turns to face, provides the starting point. A facing fish is more likely to turn broad­ side if its partner is also facing than if its partner is broadside. While being faced by its partner, the fish is more likely to flicker its pelvic fin than when the partner is broadside. Individuals differ in their tail beating response to their partner's facing orientation, some showing it more fre­ quently, and others less frequently, than when the partner is broadside. After the partner has turned to face and raised its gill covers, most pelvic fin flickering occurs in the first 1·5 sec interval afterwards. When the distribution of tail beating frequency between the successive 1·5-sec

A participant in an encounter between two like­ sexed Siamese fighting fish, that have not dis­ played at each other before, can either win or lose, and this monograph explores the relation­ ships between the outcome of an encounter and the display during it. Since both participants perform the same display movements, differences in their displays must lie in frequencies and timing of these movements. Methods for reveal­ ing such differences constitute a large part of this work. Its relation to preceding research on displays is discussed in the introduction, and the strategy of the present work is outlined. The chapter on methods describes the care, culture and handling of the fish, and stresses the importance of specifying the colours and patterns of the subjects used. Limitations of the time-event recording method are discussed. The third chapter describes the display move­ ments, presenting first an encounter between two fish as a whole. In the detailed descriptions, easily visible changes in the behaviour are emphasized. Courtship movements are also described, since courtship has many movements in common with so-called threat display. Non­ display behaviour is presented, because fish in display-eliciting situations do not always display all the time, but the situations may nevertheless affect the frequencies of these movements. The larger part of this monograph is con­ cerned with the display between like-sexed fish when they are close to each other, in which case each participant goes repeatedly through a cycle of turning to face its opponent and turning broadside. If its gill covers are not already erect, the fish raises them as it turns to face. If it lowers them while displaying, it usually does so as it turns broadside. While broadside, it may flicker the pelvic fin on the offside from its oppon­ ent and may beat and fl.ash its tail. These move­ ments may occur in any combination of sequences and frequencies, but some combinations are more common than others. 69

70

THE DISPLAY OF THE SIAMESE FIGHTING FISH, BETTA SPLENDENS

intervals of the partner's gill raising bouts is significantly non-uniform, the maximum fre­ quencies occur later rather than earlier. The temporal relation between the interval when the fish beats its tail most frequently, and the moment when the partner lowers its gill covers again, suggests that gill cover lowering is a re­ sponse to tail beating. (There was no consistent relation between pelvic fin flickering and gill cover lowering.) While the partner has its gill covers lowered, tail beating frequency may also change, often increasing steadily until the part­ ner raises its gill covers again. In the sixth chapter, the encounters between pairs of females allowed to display until one of the 'participants' gave up, were analysed by 2­ min periods. During the encounter, both fish increase the durations of their gill cover raising bouts, but the winners eventually outstrip the losers in this measure. The broadside displays of the winners and losers were compared, and winners seem less responsive in lowering their gill covers to their partners' displays. The winners are also more likely to maintain and perhaps increase their tail beating frequency as their partners' gill raising bouts increase in length. Losers bite as soon and as often as winners. Differences between the displays of different individuals, possibly relevant in deciding out­ comes, are more easily seen in situations where all the fish have the same partner, and where the partner's behaviour is unaffected by the fishes' displays. Domesticated males were exposed individually for 40 min to a stationary puppet which changed its orientation between broadside and facing every 2 min. The proportion of the whole test spent with the gill covers erect was correlated with the proportion of time spent near the puppet. With the proportion of time spent with gill covers erect was positively cor­ related the measure: total fin flickers total fin flickers+ tail beats+ tail flashes

x lOO,

and negatively correlated the measure

total tail flashes 1 total fin flickers x tail beats+tail flashes x OO. The measure tail beats while puppet faces ) . broa dst.de x lOO - lOO ( tat·1 beats wh'l 1 e puppet ts which is a measure of the effect of a change in the puppet's orientation, was also positively correlated with the proportion of the whole test spent with the gill covers erect. The remaining two chapters discuss applica­ tions of the methods used in this work, and sug­ gest further research on Betta splendens. In chapter 8, the relevance of description of the display on a time scale intermediate between the second by second one of chapter 5, and the 2­ min by 2-min one of chapters 6 and 7, is dis­ cussed in the light of the suggestion that each fish's behaviour may depend on how its oppo­ nent responded to its gill raising bout during the preceding 5 or IO sec. Chapter 9 reviews etho­ logists' interpretations of display, and discusses research suggested by the work in this mono­ graph, and by the current work on the reinforc­ ing properties of opportunities to display.

Acknowledgments The work described in this monograph was supported by an S.R.C. Studentship and carried out at the Sub-Department of Animal Behaviour, Madingley, Cambridge. I am grateful to Pro­ fessor T. Weis-Fogh and Professor W. H. Thorpe F.R.s. for the use of facilities there, and to Mr R. Rice and Mr T. Wilson for technical help. I wish to thank Mr K. Klose and Dr A. D. Woodhead for their generous advice about caring for and breeding domesticated Betta splendens, Mr P. Karnasut for sending me wild­ type fish from Bangkok, and Professor T. I. Thompson for the use of the photograph in the plate. It is a pleasure to acknowledge the en­ couragement and keen criticism of my super­ visor, Professor R. A. Hinde, and of all those who were at the Sub-Department between 1963 and 1968.

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