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Observations on the breeding and growth of the giant freshwater prawn Macrobrachium rosenbergii (de Man) in the laboratory
Aquaculture,
3 (1974) 159-174 @ Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
OBSERVATIONS ON THE BREEDING AND GROWTH OF THE GIANT FRESHWATER PRAWN Macrobrachium rosenbergi (DE MAN) IN THE LABORATORY
J.F. WICKINS and T.W. BEARD Shellfish Culture Unit, Fisheries Experiment
Station, Conwy, Wales (Great Britain)
(Received November 26, 197 3)
INTRODUCTION
The development of intensive prawn culture in a controlled environment in Great Britain will partly depend on the ability of fast-growing exotic species to mature and reproduce in captivity (Forster and Wickins, 1972). The giant freshwater prawn Mucrobruchium rosenbergii (de Man) has been considered for intensive culture (Wickins, 1972b), and this report describes observations made with 23 M. rosenbergii (3 males and 20 females) which were reared from the egg to sexual maturity in captivity. The aims of the work were to investigate the conditions in which the prawns would mature, mate and produce viable larvae in the laboratory and to estimate the yield of viable larvae that might be expected in captivity. M. rosenbergii belongs to the Caridea, a group of prawns which carry their eggs attached to modified abdominal appendages for a period of incubation, In this report the term spawning refers to the release of eggs from the genital pore prior to attachment to the pleopods. Hatching refers to the emergence of the larvae from the egg after a period of incubation. Unproductive spawning refers to eggs which were initially attached. to the pleopods but which later became detached. METHODS
The prawns used in this study were hatched at Conwy and cultured for 340 days before the observations described here commenced. During this time they were reared in crowded canditions as part of an experiment to determine the effect of population density on growth and survival (Wickins, 1972b). It is possible that stresses experienced during this period
160 influenced their later growth and reproductive ability (see Results). Observations on the prawns were made over a subsequent period of 390 days (from November 1970 to December 197 1). The prawns were kept separately in white polythene tanks measuring either 57 x 37 x 25 cm deep or 48 x 28 x 25 cm deep. Each tank received a flow of water (28 + l”C, 5%0 salinity) of about 24 I/hour from a.400 litre glass-tibre reservoir tank. All the culture tanks were gently aerated and more vigorous aeration was given to the reservoir. The brackish water was produced by mixing Conwy tap water and sea water from the laboratory supply (Wickins, 1972b). It was recycled continuously through a percolating biological filter (Forster and Wickins, 1972) 48 cm diameter, 46 cm high, at a rate of 720 l/hour. The column of 2-4 cm diameter gravel in the falter was covered by a layer of oyster shell. Some water was lost from the system by evaporation and also when siphoning the uneaten food from the tanks each day. These losses were made up daily and the salinity was adjusted when necessary. Throughout the first 220 days, 3% of the water was changed every day but the oyster shell on the filter was not changed or disturbed; during this period the pH fell from 7.5 to 5.5. For the last 170 days, 7% of the water was removed each day and the oyster shell renewed regularly; during this period the pH remained between 6.4 and 7.4. Freshly opened mussels (Mytilus edulis L.) were supplied daily as food and, at the same time, uneaten food from the previous day and detritus were removed. Once each week frozen shrimps (Crangon crangon (L.)) were given as a food supplement. Artificial illumination was used and did not exceed 10 lm/ft2 (approx. 0.1 m2 ) at the water surface. Periods of illumination were irregular during the first 150 days of the experiment, usually between 8 and 24 h;but for the remaining 240 days it was restricted to 8 h each day. An 8-litre polythene bucket was placed under the overflow of any tank containing a female about to release larvae. The larvae, as they hatched, were carried by the water current into the bucket where they were caught by a 250 E.tmmesh filter (Wickins, 1972a). An estimate of the size of each brood was made by placing the larvae in 2-30 1 of water - the larger the brood, the larger the quantity of water - and then counting the animals contained in five 100 ml samples. The mean percentage standard error of these estimates ranged from 1.5% to 9.9%, with one value at 15.9%; the overall mean was 4.4%. Live larvae were measured with a low-power binocular microscope fitted with an eyepiece graticule. They were placed in a drop of water on the stage and manipulated into an extended position with a fine paint brush while the water was removed with a narrow bore pipette. Measure ments were made from the tip of the rostrum to the tip of the telson.
161
Records were kept of the frequency of moulting of the adults, the number of times they mated and spawned, and the fate of their eggs. Adult prawns were measured by holding them against a graduated rule (Wickins, 1972a). Measurements were made at approximately the middle of each intermoult period, or immediately after larvae had hatched. Female prawns were inspected each day for signs of maturity. Ripe females were recognized by the conspicuous orange gonads visible through the dorsal and lateral areas of the carapace. As mating usually occurs within 24 h of the pre-spawning moult of the female prawn (Rae, 1965). a male was placed with a ripe female that had moulted within the past 24 h: after a period of l-4 h (usually 1 h) the male was removed. We were reluctant to disturb ovigerous females lest their eggs became detached or were eaten; however, they were inspected every 7-10 days to check the development of the eggs. Unfertilized eggs were normally lost within 2-3 days of spawning (Ling, 1969). Some batches of fertilized eggs which had developed eyespots - a sign of advanced development - were lost in some trials. EXPERIMENTAL
RESULTS
The results are divided into two parts, those recorded during the first 220 days (part 1) and those recorded over the remaining 170 days (part 2) of the experiment. This has been done because of the reduced control over the photoperiod and the pH of the water during part 1 (see Methods), and because it was apparent that the increased control of these two factors during part 2 affected the animals. In addition the crowded conditions in which the prawns had been reared prior to the experiment may have in~uenced their growth and reproduction, and such effects would probably have been greater in the first than in the second period of observation. Division of the results in this way allowed the effect on the prawns of the more stable conditions of part 2 to be compared with the effects of the environment during part 1. Number of larvae
The number of larvae that hatched from each brood ranged from only 50 to 98 100, with a mean of 24 000 (Table I). .During part 1 there was no correlation between number of larvae and the size of the female parent (Fig. 1A), but in part 2 there was a proportional increase in the brood size as the size of the female increased. (Fig. IB). During this time broods contained over 20 000 larvae, with one exception of 7 000. The slope of the fitted line was found to be significantly different from 0 (variance
162 TABLE I The number and mean lengths of newly hatched larvae of Macrobrachium Male reference letter
Female reference number
Total length of female
2 2 4* 5* 5* 5 I 11 12* 13 13 13 16* 17
148 154 145 130 132 165 133 174 132 137 146 155 132 133
1 1* 1* 4* 4 5 8* 8 8* 11 13 13* 13* 16 16 17* 17
180 220 230 170 _
(mm)
Number of larvae hatched
rosenbergii
Mean length of larvae
S.E.
(mm)
Part 1 A A B A A A A A A B B A B A
2 250 100 6 068 900 20 730 12 840 463 3 000 6 360 640 50 42 380 329 192
2.1 _
0.010 _
2.1 _
0.005 -
2.1 2.1 2.0 2.2 2.1 2.1 -
0.008 0.014 0.013 0.015 0.006 0.009 _
2.0 2.1 2.1
0.014 0.007 0.009
2.0 _ _
0.015 _
2.0 2.0 2.1 1.9 _ _
0.012 0.010 0.011 0.012 _ _
1.9 1.9 2.1 2.0 1.9 1.9 1.9 2.1
0.020 0.015 0.016 0.011 0.017 0.017 0.019 0.007
Fart 2 A A A B A A B B A A B B A A A B A
200 160 175 220 185 157 169 200 173 182 170 190
82 98 54 24 17 51 20 35 33 34 7 37 82 55 -
320 100 510 970 148 744 160 100 420 560 840 218 400 440
27 513 24 939
*Larvae hatched on two successive nights (see Table III)
ratio (F) = 7.163, d.f. 1, 13, 0.05 > P > 0.01). This showed that in part 2 larger females tended to produce larger broods, but in part 1 brood size varied considerably (from 50 larvae in one brood to 42 380 in another) regardless of female size. The relationships between length of larvae at hatching and size of the
163
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150
175
TOTAL
LENGTH
OF
FEMALE
1000 ~~~
260 (mm)
t 1 150 TOTAL
1 175 LENGTH
200 OF
225 FEMALE
I 250 (mm)
Fig. 1. The relation between the number of larvae produced and the length of the parent female Mucrobrachium rosenbergii during (A) part 1 and (B) part 2 of the experiment. The calculated regression line is drawn from the equation: log, 0 number of larvae = 3.2099 + 0.00132 total length (correlation coefficient (r) = 0.596, d.f. 13, 0.02 > P > 0.01).
female parent (Fig.2) and brood size (Fig.3) were inconclusive. When results from parts 1 and 2 were combined there was a tendency for larval size to decrease with increasing female size (0.05 > P < 0.1) (see Table I and Fig.2) and with increasing brood size (P < 0.05) (Fig.3). However, data from part 2 showed a positive correlation between larval size and adult size, which was significant at the 5% level. Growth during egg production
It is generally expected that growth of the female will be reduced during egg development, since a proportion of the available energy is used for the development of the oocytes. It may be assumed that inM. rosey1bergii the majority of eggs develop in one intermoult period, since a total of 14 females spawned on 34 consecutive moults.
164 100 000
r
-
0
0
x
> x 10 000
-
n 8
s E
P-SO 05
a
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1000
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x
4
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6 2 2 TOTAL
LENGTH
OF
FEMALE
(mm)
x
100 19
I
LENGTH
OF
I
I
20
21 LARVAE
22 (mm)
2. The relation between the length of larvae and the length of the parent female brachium wsetzbergii. Crosses represent data from part 1, open circles those from part calculated regression line for the combined data is drawn from the equation: larval length = 2.23848-0.001326 female length (r=-0.3655,d.f.21,0.05
Mucro2. The
Crosses for the
Increment
The increases in length at moulting. of female prawns that were and were not producing eggs are compared in Fig.4. Length before moulting was plotted against length after moulting for females in which eggs developed during the previous intermoult period, and which spawned immediately after the moult in question. This was compared with similar plots for females that were not producing eggs. Data from the two parts of the experiment are shown separately. In part 1 the values of b (slope) fell within the range b > 0.95 < 1.05 set by Kurata (1962) as defining arithmetic growth, i.e. constant increments were added at each moult (Fig.4A and B), but in part 2 the values of b were larger (1.14 and 1.05) and were outside Kurata’s arithmetic range (Fig.4C and D). There were fewer measurements available from part 2 than from part 1, which gave larger standard errors of b, as shown in Fig.4C and D. This meant that no one slope differed from another at the 5% level of significance. When part
165 200-
(A,
180
-
160
-
240-
CL.)
._,
:
140 =0994:0063 120-
100 -
160
140 J
‘; c =1037~0098
120
ITHOUT
100 100
120
340
WITHOUT
EGGS
160
180
113
!60
L”
181)
EGGS
200
220
L”
Fig. 4. Hiatt diagrams (Hiatt, 1948) which show the growth pattern of mature female Mucrobrachium rosenbergii. The regression lines are drawn from the equations: (a) y = 7.2914 + 0.9937 x (r = 0.9846, d.f. 33, P < 0.001) (b)y = 3.3357 + 1.0371 x (r = 0.9639, d.f. 35, P < 0.001) (c)y = -11.7469 + 1.1435 x (r = 0.9159, d.f. 13, P< 0.001) (d)y = 6.2716 + 1.0512 x (r = 0.8626, d.f. 5, 0.02 > P > 0.01) where y = premoult length (mm) and x = post-moult length (mm)
1 was compared with part 2, regardless 95% confidence limits of b were: Value of slope ‘b’ Part 1 1.01 Part 2 1.12
of egg production, 95% confidence 0.95-1.07 0.88- 1.36
the values and limits of ‘b’
This indicated that arithmetic growth was a less accurate description of the growth of the females during the second part of the experiment. The mean length increments achieved by each group at a moult were: Eggs produced mm 95% limits 6.43 5.547.32 Part 1 13.07 7.19-18.94 Part 2 There
was no significant
Eggs not produced mm 95% limits 7.90 6.589.22 14.71 7.15-22.28 difference
Total mm 7.20 13.59
in the mean increment
95% limits 6.39-8.02 9.28-17.91 due to egg
166 260
x
MALES
.
FEMALES
t :oo---
.
:
lt 400 AGE
I
PART 1 -bPART2 *
500 IN
DAYS
f-‘ROM
,
8
600
700
HATCHING
fig. 5. The relationshjp of age to length of ~ffcrob~u&kiu~ ~osenbe~gij m~ntained calculated regression Iines are drawn from the equations: Maie length = 47.4659 + 0.2133 Age V = 0.9277, d.f. 18, P< 0.001) and Female lengrh = 36.6178 + 0.2320 Age (v = 0.9028, d.t: 121, P < 0.001)
in captivity.
The
production in either part 1 or part 2, but when the data were combined the mean increment was significantly larger (P < 0.05) during part 2 than part 1. Regressions of increment on original length were also calculated but there were no significant changes of increment with increase in size at the 5% level of significance in any of the groups tested. Growth was thus more likely to be arithmetic than geometric, and the greater mean increments in part 2 were probably indicative of a trend towards progressive geometic growth, but evidence for this is slight. The overall growth of males and females throughout the experiment is shown in Fig.5. lntermoult period
A comparison was made between the length of intermoult periods which preceded spawning and those which did not. In the first case eggs were developing and therefore using some of the prawns’ resources, whereas in the second more energy was available for somatic growth. The results showed that there was no correlation of intermoult period with length of the prawn except during part 1 in the case of females that were not producing eggs (Fig.@. In this,group the intermoult period increased proportionately with length.
167
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“; ; z -
20-
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. 10 100
a,*
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.
I
I
110
120
TOTAL
-1 130 LENGTH
I
I
I
1
I
140
150
160
170
18C
b-m)
Fig. 6. The relation between intermoult period and length of female Macrobrachium rosenbergii that were not producing eggs, during part 1 of the experiment. The calculated regression line is drawn from the equation: Intermoult period = -2.82714 + 0.264996 total length (r = 0.321055, d.f. 51, 0.05 > P > 0.02)
The mean intermoult period during part 1 was significantly longer when eggs were being formed (38 days, s.e. 1.63, d.f. 43) than when they were not (31 days, s.e. 1.64, d.f. 60) (‘t’ test, P < 0.05). During part 2 prawns moulted at the same rate whether they were producing eggs (mean 43 days s.e. 2.799, d.f. 14) or not (mean 46 days, s.e. 3.200, d.f. 13). In the case of females that produced larvae the period between hatching of the eggs and the next moult varied between 9 and 37 days; it was longer (mean 34 days, s.e. 1.26, d.f. 3) when eggs were spawned at the following moult than when spawning did not occur (mean 16 days, s.e. 3.13, d.f. 5) (P < 0.05). The delay in moulting was thought to be associated with the development of oocytes in the ovaries. Spawning, incubation
and hatching
In Table II the number of times each female spawned and hatched larvae, and the total numbers of larvae produced by each female, are shown. One female did not spawn at all, eight others spawned once or twice but lost their eggs, and only 11 of the total number of 20 females produced live larvae. The mean number of broods from these 11 females lost following 37 of the total number of 68 was 2.82. Eggs-were spawnings. Three females spawned more than four times at successive moults and one produced larvae five times at successive moults. After the eggs were spawned they remained attached to the abdominal
168 TABLE II The spawning and larval production of Macrobrachium lasted 390 days Reference number of female
rosenbergii during an experiment
Total number of Spawnings
Hatches
Larvae
1 2 3
9 2 1
3 2 0
234 930 2 350 _
4 5 6
4 5 1
3 4 0
‘48 186 86 214 -
I 8 9 10
4 5 1 2
1 3 0 0
463 88 680 _ -
11 12 13 14 15
4 6 1 0 2
2 1 6 0 0
31560 6 360 166 630 _ _
16 17 18 19 20
6 5 1 1 2
3* 3 0 0 0
55 169 42 644 _ _ -
Totals
which
68
31
769 786
* The number of larvae in one of the broods was not determined
pleopods for an incubation period which lasted 19-22 days (mean 19.9 days, s.e. 0.134, d.f. 3 1) which is in agreement with the observations of John (1957) and Rao (1965). Eighteen of the broods hatched in one night, but 13 others took two nights to complete hatching (Table III). In the latter group there were no significant differences between the proportion of larvae in each brood that hatched on the first night (49%, range 6.9-92.8%) and those that hatched on the second (51%, range 7.2-93.1%) (P > 0.1). Similarly there were no significant differences in the mean lengths of larvae which hatched on the first and second nights (see Discussion). Samples of 20 larvae taken at random from each brood were measured and were between 1.9 and 2.1 mm (mean 2.0 mm) total length. In Fig.7 the experimental period is divided into consecutive 30 day intervals for which are shown the mean numbers of larvae per brood (line A), the total number of broods that hatched (line B), and the number of
169 TABLE III The number of larvae of Macrobrachium Reference number of female
First night Number of larvae
rosenbergii
that hatched on two successive nights
%
Second night Number of % larvae
First night Mean S.E. length
Second night Mean SE. length ~_.___
120 800 2 910 3 120 219
13.5 87.5 16.3 29.0 49.8
5 348 100 17 820 2 640 110
86.5 12.5 83.7 71.0 50.2
2.1 _ 2.1 2.1 2.1
0.007
2.1 _
0.006
0.013 0.009 0.009
2.1 2.1 2.0
0.008 0.008 0.010
33 600 20 560 18 800 8 244 70 852 1 714
52.1 18.5 92.8 28.5 83.7 6.9
64 500 4 410 1 360 28 914 11 548 25 739
41.9 21.5 1.2 71.5 16.3 93.1
_
Part 1 4 5 5 12 16 Part 2 1* 4 8* 13 13 17
1.9 1.9
_ 0.017 0.018
2.0 1.9 _
0.018 0.015
0.015
2.0 -
0.008
2.0 _
* Data for one brood not available (see Table 1).
100000 r
4” 10000
f----*
-
2 4
b
1000
-
n ii f
100 -
z
TIME
(30
DAY
P’ERI~OS)
Fig. 7. The mean number of larvae per brood (line A), the number of times spawning was successful (line B) and unsuccessful (line C) in an experiment with Macrobrachium rosenbergii reared in captivity.
170 times eggs were spawned but did not hatch (line C). For example, in the third 30 day period, which corresponds approximately to January 1971, 14 females spawned; of these, five retained their eggs and produced larvae. The mean number of larvae per brood was 2 600. Nine of the females lost their eggs before incubation was completed. The unproductive spawnings were more frequent than productive spawnings during the first seven periods, but after this time (May-June 197 1) the production of larvae was consistently higher and the number of unproductive spawnings was less than the productive (see Discussion). Males
Three males were used in this study and the number of times that mating was successful in each intermoult period is shown in Table IV. A successful mating resulted in viable larvae being produced by the female 20 days after copulation. The large proportion of matings that were unsuccessful during part 1 may have been due to adverse environmental conditions affecting either the males, the females or the eggs and their
I
1
‘40
,
1
!60
180 L,
I
200
I
220
(mm)
Fig. 8. Hiatt diagram (Hiatt, 1948) which shows the growth pattern of three male Mucrobrachium rosenbergii. The calculated regression line is drawn from the equation: Post-moult length = 3.2105 + 1.0557 pre-moult length (r = 0.8962, d.f. 15, P < 0.001)
171 TABLE IV The frequency with which each male Macrobrachium
rosenbergii mated in each intermoult
period _
Male tag
Length of intermoult period (days)
A
42 30 51 33 34 98
Number of successful matings
Total number of opportunities including successful matings 13 4 12 I 6 8
June 1971 25 Data incomplete B
26 49 36 38 45
June 1971 34 41 Data incomplete C
58 31 56 46
June 1971 Data incomplete
0
1
supporting membranes. It is not known why male C (Table IV) did not sire any larvae. The growth of the males is shown in Fig. 8. Growth was best described as arithmetic (although b = 1.056), since the standard error of b was sufficiently large to give 95% confidence limits of 0.8579- 1.2535, and because there was no significant correlation of increment and total length. There were no differences in the mean increments between individual males during either part of the exp.eriment. The combined data gave a mean length increment of 13.0 mm with 95% confidence limits of 9.23-16.77 mm, and this was similar to the mean increment (13.89 mm)
172
achieved by females during part 2. The mean intermoult period was 41.9 days (s.e. 9.89, d.f. 17) and was independent of the size of the prawn (Y= 0.04808, d.f. 16, P> 0.1). DISCUSSION
The reduced control of pH and photoperiod during the first 220 days (part 1) of the experiment may have produced a lasting effect on the reproductive potential of the prawns. The results show a distinct improvement in the reproductive ability of the animals after the environmental conditions were more constant. We consider that the control of photoperiod and pH exercised during part 2 of the experiment was beneficial to the prawns and, secondly, that the overall performance of the prawns (in terms of the number of larvae and broods produced per unit time) was improved. The first postulate is supported by the observed increase in mean brood size which occurred after 220 days and was maintained throughout part 2. Similarly, the number of times females spawned and lost their eggs, frequently after carrying them until eyespots had developed, was less in part 2 than in part 1. Our results compare favourably with those of Ling (1969), who reported that female M. rosenbergii kept in the laboratory were able to lay eggs twice within five months; he thought that they may be able to spawn 3-4 times in one year under natural conditions. In the experiment reported here eight females spawned two and three times, and one produced viable larvae four times, in the 170 days of part 2 of the experiment. The change in the environmental conditions may also have influenced the growth of the prawns. In parts 1 and 2 growth was arithmetic regardless of egg production, although in part 2 the mean length increment was larger (7.2 cf. 13.6 mm) (P < 0.05). The moulting frequency was very variable in all the four groups shown in Fig. 6, and the intermoult periods of females that were not producing eggs during part 1 increased with size. It should be noted that these females were mature (see below), since they produced eggs during other intermoult periods in part 1. In the other three groups there was no correlation of intermoult period with size and the mean intermoult periods did not differ significantly (P > 0.05). There was no evidence for progressive geometric growth and this possibly indicates that the smaller increments achieved at each moult in part 1 were a result of the less well controlled conditions. Kamiguchi (1971) found that the intermoult period of sexually immature Palaemon paucidens increased with size, but mature specimens moulted at approximately constant inter-
173
vals. His prawns also increased in length by a constant amount at each moult throughout the range studied (Kamiguchi, 1973, personal communication). Variations in the mean length of larvae from each brood also occurred, but there was no relation between larval size and either brood size or adult size. It might be expected, for example, that smaller larvae would hatch from the larger broods, due to less yolk being available for each egg or to the effects of physical crowding. No explanation is available for the significant positive correlation between larval size and adult size in the data from part 2. Some broods took two nights to complete hatching. Pandian and Katre ( 1972) found that the larvae of ~uc~o~~~c~~~~ idae Heller which hatched on the second night were 2% longer than those which hatched on the first night. Our larvae were too small (2 mm compared with the 5 mm of M: idae) for differences of this magnitude to be detected. Fecundity is usually determined by estimates of the number of eggs spawned by a given size group of females. The figure obtained in this way for caridean prawns is frequently higher than estimates of the number of live larvae produced, presumably because of mortality during incubation (Reeve, 1969). Rajyal~shmi ( 196 1) found the relationship between length and fecundity (expressed as the number of ova) in M. rosenbergii (Palaemon carcinus Fabr.) to be: log, ,, number of ova = -2.7949 + 3.3209 log, 0 female length (1) Our results were described by the equation: log, ,, number of larvae = 3.01036 -+3.34477 log, e female length (2) Eq. 1 may be solved to demonstrate that a 200 mm female produces 70 230 eggs and a 160 mm female produces 33 470 eggs; from eq. 2 the same sizes of female would give 48 530 and 23 010 larvae respectively, a difference of about 3 1%. It is not known if mortality during incubation is likely to be as high as this, and some of the difference probably results from the different populations that were studied.
Three male and 20 female prawns, ~acrobr~c~~~~ rosenbergii (de Man), were observed for 390 days. They were maintained in brackish water (5%0 salinity) at 28°C which was recycled continuously through a percolating biological filter. Illumination was artificial and did not exceed 10 lm/ft2 (approx. 0.1 m2 ) at the water surface. Mating readily occurred in the experimental tanks (48 x 28 x 25 cm deep). Eggs were incubated for 20 days; the mean number of larvae per brood was 24 000 (range 50-98 100). Over 750 000 larvae were hatched during the experiment.
174
Larger females had proportionately larger broods and larvae from seven broods were cultured to the post-larval stage at intervals throughout the experimental period, which demonstrated their viability. The increase in length of the adults at each moult was constant (arithmetic growth) and did not alter when ova were maturing in the ovary. Prawns achieved larger mean length increments after the environmental conditions were improved. The moulting frequency was very variable and, with one exception, did not change proportionately with length or age of the prawns. Females grew from 115 to 205 mm and males from 145 to 230 mm total length. Three females spawned more than four times in successive intermoult periods, and one produced viable larvae five times in succession. Two of the males sired viable larvae four and seven times respectively during one intermoult period. ACKNOWLEDGEMENTS
We acknowledge the assistance of Mr G. Williams in this work. REFERENCES Forster, J.R.M. and Wickins, J.F. (1972) Prawn culture in the United Kingdom: its status and potential. Lab. Leafl. Fish. Lab. Lowestoft, (New Series) No. 27, 32 pp. Hiatt, R.W. (1948) The biology of the lined shore crab Pachygrapsus crassipes Randall. Pacif Sci, 2,135-213.
John, C.M. (1957) Bionomics and life history of Macrobrachium rosenbergii (de Man). Bull. cent Res. Inst. Univ. Travancore, Ser. C, 5 (l), 93-102. Kamiguchi, Y. (1971) Studies on the molting in the freshwater prawn, Palaemon paucidens. I. Some endogenous and exogenous factors influencing the intermolt cycle. J. Fat. Sci Hokkaido Univ., Ser. VI, ZooL 18 (l), 15-23. Kurata, H. (1962) Studies on the age and growth of crustacea. Bull. Hokkaido reg. Fish. Res. Lab., No. 24, 1-115. Ling, SW. (1969) The general biology and development of Macrobrachium rosenbergii (de Man). Fish. Rep. F.A.O.,
57 (3), 589-606.
Pandian, T.J. and Katre, S. (1972) Effect of hatching time on larval mortality and survival of the prawn Macrobrachium idae. Mar. Biol., 13, 330-337. Rajyalaksmi, T. (1961) Studies on maturation and breeding in some estuarine palaemonid prawns. Proc. natn. Inst. Sci India, 27B (4), 179-188. Rao, R.M. (1965) Breeding behaviour in Macrobrachium rosenbergii (de Man). Fishery Technology, 2 (l), 19-25. Reeve, M.R. (1969) The laboratory culture of the prawn Paloemon serratus. Fishery Invest., Lond., Ser. 2, 26 (l), 38 pp. Wickins, J.F. (1972a) Developments in the laboratory culture of the common prawn Palaemon serratus Pennant. Fishery Invest., Lond, Ser. 2, 27 (4), 23 pp. Wickins, J.F. (1972b) Experiments on the culture of the spot prawn Pandalus plcltyceros Brandt and the giant freshwater prawn Macrobrachium rosenbergii (de Man). Fishery Invest., Land, Ser. 2, 27 (5), 23 pp.
3 (1974) 159-174 @ Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
OBSERVATIONS ON THE BREEDING AND GROWTH OF THE GIANT FRESHWATER PRAWN Macrobrachium rosenbergi (DE MAN) IN THE LABORATORY
J.F. WICKINS and T.W. BEARD Shellfish Culture Unit, Fisheries Experiment
Station, Conwy, Wales (Great Britain)
(Received November 26, 197 3)
INTRODUCTION
The development of intensive prawn culture in a controlled environment in Great Britain will partly depend on the ability of fast-growing exotic species to mature and reproduce in captivity (Forster and Wickins, 1972). The giant freshwater prawn Mucrobruchium rosenbergii (de Man) has been considered for intensive culture (Wickins, 1972b), and this report describes observations made with 23 M. rosenbergii (3 males and 20 females) which were reared from the egg to sexual maturity in captivity. The aims of the work were to investigate the conditions in which the prawns would mature, mate and produce viable larvae in the laboratory and to estimate the yield of viable larvae that might be expected in captivity. M. rosenbergii belongs to the Caridea, a group of prawns which carry their eggs attached to modified abdominal appendages for a period of incubation, In this report the term spawning refers to the release of eggs from the genital pore prior to attachment to the pleopods. Hatching refers to the emergence of the larvae from the egg after a period of incubation. Unproductive spawning refers to eggs which were initially attached. to the pleopods but which later became detached. METHODS
The prawns used in this study were hatched at Conwy and cultured for 340 days before the observations described here commenced. During this time they were reared in crowded canditions as part of an experiment to determine the effect of population density on growth and survival (Wickins, 1972b). It is possible that stresses experienced during this period
160 influenced their later growth and reproductive ability (see Results). Observations on the prawns were made over a subsequent period of 390 days (from November 1970 to December 197 1). The prawns were kept separately in white polythene tanks measuring either 57 x 37 x 25 cm deep or 48 x 28 x 25 cm deep. Each tank received a flow of water (28 + l”C, 5%0 salinity) of about 24 I/hour from a.400 litre glass-tibre reservoir tank. All the culture tanks were gently aerated and more vigorous aeration was given to the reservoir. The brackish water was produced by mixing Conwy tap water and sea water from the laboratory supply (Wickins, 1972b). It was recycled continuously through a percolating biological filter (Forster and Wickins, 1972) 48 cm diameter, 46 cm high, at a rate of 720 l/hour. The column of 2-4 cm diameter gravel in the falter was covered by a layer of oyster shell. Some water was lost from the system by evaporation and also when siphoning the uneaten food from the tanks each day. These losses were made up daily and the salinity was adjusted when necessary. Throughout the first 220 days, 3% of the water was changed every day but the oyster shell on the filter was not changed or disturbed; during this period the pH fell from 7.5 to 5.5. For the last 170 days, 7% of the water was removed each day and the oyster shell renewed regularly; during this period the pH remained between 6.4 and 7.4. Freshly opened mussels (Mytilus edulis L.) were supplied daily as food and, at the same time, uneaten food from the previous day and detritus were removed. Once each week frozen shrimps (Crangon crangon (L.)) were given as a food supplement. Artificial illumination was used and did not exceed 10 lm/ft2 (approx. 0.1 m2 ) at the water surface. Periods of illumination were irregular during the first 150 days of the experiment, usually between 8 and 24 h;but for the remaining 240 days it was restricted to 8 h each day. An 8-litre polythene bucket was placed under the overflow of any tank containing a female about to release larvae. The larvae, as they hatched, were carried by the water current into the bucket where they were caught by a 250 E.tmmesh filter (Wickins, 1972a). An estimate of the size of each brood was made by placing the larvae in 2-30 1 of water - the larger the brood, the larger the quantity of water - and then counting the animals contained in five 100 ml samples. The mean percentage standard error of these estimates ranged from 1.5% to 9.9%, with one value at 15.9%; the overall mean was 4.4%. Live larvae were measured with a low-power binocular microscope fitted with an eyepiece graticule. They were placed in a drop of water on the stage and manipulated into an extended position with a fine paint brush while the water was removed with a narrow bore pipette. Measure ments were made from the tip of the rostrum to the tip of the telson.
161
Records were kept of the frequency of moulting of the adults, the number of times they mated and spawned, and the fate of their eggs. Adult prawns were measured by holding them against a graduated rule (Wickins, 1972a). Measurements were made at approximately the middle of each intermoult period, or immediately after larvae had hatched. Female prawns were inspected each day for signs of maturity. Ripe females were recognized by the conspicuous orange gonads visible through the dorsal and lateral areas of the carapace. As mating usually occurs within 24 h of the pre-spawning moult of the female prawn (Rae, 1965). a male was placed with a ripe female that had moulted within the past 24 h: after a period of l-4 h (usually 1 h) the male was removed. We were reluctant to disturb ovigerous females lest their eggs became detached or were eaten; however, they were inspected every 7-10 days to check the development of the eggs. Unfertilized eggs were normally lost within 2-3 days of spawning (Ling, 1969). Some batches of fertilized eggs which had developed eyespots - a sign of advanced development - were lost in some trials. EXPERIMENTAL
RESULTS
The results are divided into two parts, those recorded during the first 220 days (part 1) and those recorded over the remaining 170 days (part 2) of the experiment. This has been done because of the reduced control over the photoperiod and the pH of the water during part 1 (see Methods), and because it was apparent that the increased control of these two factors during part 2 affected the animals. In addition the crowded conditions in which the prawns had been reared prior to the experiment may have in~uenced their growth and reproduction, and such effects would probably have been greater in the first than in the second period of observation. Division of the results in this way allowed the effect on the prawns of the more stable conditions of part 2 to be compared with the effects of the environment during part 1. Number of larvae
The number of larvae that hatched from each brood ranged from only 50 to 98 100, with a mean of 24 000 (Table I). .During part 1 there was no correlation between number of larvae and the size of the female parent (Fig. 1A), but in part 2 there was a proportional increase in the brood size as the size of the female increased. (Fig. IB). During this time broods contained over 20 000 larvae, with one exception of 7 000. The slope of the fitted line was found to be significantly different from 0 (variance
162 TABLE I The number and mean lengths of newly hatched larvae of Macrobrachium Male reference letter
Female reference number
Total length of female
2 2 4* 5* 5* 5 I 11 12* 13 13 13 16* 17
148 154 145 130 132 165 133 174 132 137 146 155 132 133
1 1* 1* 4* 4 5 8* 8 8* 11 13 13* 13* 16 16 17* 17
180 220 230 170 _
(mm)
Number of larvae hatched
rosenbergii
Mean length of larvae
S.E.
(mm)
Part 1 A A B A A A A A A B B A B A
2 250 100 6 068 900 20 730 12 840 463 3 000 6 360 640 50 42 380 329 192
2.1 _
0.010 _
2.1 _
0.005 -
2.1 2.1 2.0 2.2 2.1 2.1 -
0.008 0.014 0.013 0.015 0.006 0.009 _
2.0 2.1 2.1
0.014 0.007 0.009
2.0 _ _
0.015 _
2.0 2.0 2.1 1.9 _ _
0.012 0.010 0.011 0.012 _ _
1.9 1.9 2.1 2.0 1.9 1.9 1.9 2.1
0.020 0.015 0.016 0.011 0.017 0.017 0.019 0.007
Fart 2 A A A B A A B B A A B B A A A B A
200 160 175 220 185 157 169 200 173 182 170 190
82 98 54 24 17 51 20 35 33 34 7 37 82 55 -
320 100 510 970 148 744 160 100 420 560 840 218 400 440
27 513 24 939
*Larvae hatched on two successive nights (see Table III)
ratio (F) = 7.163, d.f. 1, 13, 0.05 > P > 0.01). This showed that in part 2 larger females tended to produce larger broods, but in part 1 brood size varied considerably (from 50 larvae in one brood to 42 380 in another) regardless of female size. The relationships between length of larvae at hatching and size of the
163
. . .
10000 l
.
. .
100030
1000!2
1000 . .
8
.
i
g
E
.
% :2 100 3 B E5
40000
1
.
.
.
l* .
K LL :
l
-
al
.
. .
/ .
20000-
.
.
. P
2 Q J
.
LL
0 (I
s
1oorJTl
I .
z
3
10
L I
I
I
I
100
125
150
175
TOTAL
LENGTH
OF
FEMALE
1000 ~~~
260 (mm)
t 1 150 TOTAL
1 175 LENGTH
200 OF
225 FEMALE
I 250 (mm)
Fig. 1. The relation between the number of larvae produced and the length of the parent female Mucrobrachium rosenbergii during (A) part 1 and (B) part 2 of the experiment. The calculated regression line is drawn from the equation: log, 0 number of larvae = 3.2099 + 0.00132 total length (correlation coefficient (r) = 0.596, d.f. 13, 0.02 > P > 0.01).
female parent (Fig.2) and brood size (Fig.3) were inconclusive. When results from parts 1 and 2 were combined there was a tendency for larval size to decrease with increasing female size (0.05 > P < 0.1) (see Table I and Fig.2) and with increasing brood size (P < 0.05) (Fig.3). However, data from part 2 showed a positive correlation between larval size and adult size, which was significant at the 5% level. Growth during egg production
It is generally expected that growth of the female will be reduced during egg development, since a proportion of the available energy is used for the development of the oocytes. It may be assumed that inM. rosey1bergii the majority of eggs develop in one intermoult period, since a total of 14 females spawned on 34 consecutive moults.
164 100 000
r
-
0
0
x
> x 10 000
-
n 8
s E
P-SO 05
a
s
1000
-
2
x
4
x
8
x
6 2 2 TOTAL
LENGTH
OF
FEMALE
(mm)
x
100 19
I
LENGTH
OF
I
I
20
21 LARVAE
22 (mm)
2. The relation between the length of larvae and the length of the parent female brachium wsetzbergii. Crosses represent data from part 1, open circles those from part calculated regression line for the combined data is drawn from the equation: larval length = 2.23848-0.001326 female length (r=-0.3655,d.f.21,0.05
Mucro2. The
Crosses for the
Increment
The increases in length at moulting. of female prawns that were and were not producing eggs are compared in Fig.4. Length before moulting was plotted against length after moulting for females in which eggs developed during the previous intermoult period, and which spawned immediately after the moult in question. This was compared with similar plots for females that were not producing eggs. Data from the two parts of the experiment are shown separately. In part 1 the values of b (slope) fell within the range b > 0.95 < 1.05 set by Kurata (1962) as defining arithmetic growth, i.e. constant increments were added at each moult (Fig.4A and B), but in part 2 the values of b were larger (1.14 and 1.05) and were outside Kurata’s arithmetic range (Fig.4C and D). There were fewer measurements available from part 2 than from part 1, which gave larger standard errors of b, as shown in Fig.4C and D. This meant that no one slope differed from another at the 5% level of significance. When part
165 200-
(A,
180
-
160
-
240-
CL.)
._,
:
140 =0994:0063 120-
100 -
160
140 J
‘; c =1037~0098
120
ITHOUT
100 100
120
340
WITHOUT
EGGS
160
180
113
!60
L”
181)
EGGS
200
220
L”
Fig. 4. Hiatt diagrams (Hiatt, 1948) which show the growth pattern of mature female Mucrobrachium rosenbergii. The regression lines are drawn from the equations: (a) y = 7.2914 + 0.9937 x (r = 0.9846, d.f. 33, P < 0.001) (b)y = 3.3357 + 1.0371 x (r = 0.9639, d.f. 35, P < 0.001) (c)y = -11.7469 + 1.1435 x (r = 0.9159, d.f. 13, P< 0.001) (d)y = 6.2716 + 1.0512 x (r = 0.8626, d.f. 5, 0.02 > P > 0.01) where y = premoult length (mm) and x = post-moult length (mm)
1 was compared with part 2, regardless 95% confidence limits of b were: Value of slope ‘b’ Part 1 1.01 Part 2 1.12
of egg production, 95% confidence 0.95-1.07 0.88- 1.36
the values and limits of ‘b’
This indicated that arithmetic growth was a less accurate description of the growth of the females during the second part of the experiment. The mean length increments achieved by each group at a moult were: Eggs produced mm 95% limits 6.43 5.547.32 Part 1 13.07 7.19-18.94 Part 2 There
was no significant
Eggs not produced mm 95% limits 7.90 6.589.22 14.71 7.15-22.28 difference
Total mm 7.20 13.59
in the mean increment
95% limits 6.39-8.02 9.28-17.91 due to egg
166 260
x
MALES
.
FEMALES
t :oo---
.
:
lt 400 AGE
I
PART 1 -bPART2 *
500 IN
DAYS
f-‘ROM
,
8
600
700
HATCHING
fig. 5. The relationshjp of age to length of ~ffcrob~u&kiu~ ~osenbe~gij m~ntained calculated regression Iines are drawn from the equations: Maie length = 47.4659 + 0.2133 Age V = 0.9277, d.f. 18, P< 0.001) and Female lengrh = 36.6178 + 0.2320 Age (v = 0.9028, d.t: 121, P < 0.001)
in captivity.
The
production in either part 1 or part 2, but when the data were combined the mean increment was significantly larger (P < 0.05) during part 2 than part 1. Regressions of increment on original length were also calculated but there were no significant changes of increment with increase in size at the 5% level of significance in any of the groups tested. Growth was thus more likely to be arithmetic than geometric, and the greater mean increments in part 2 were probably indicative of a trend towards progressive geometic growth, but evidence for this is slight. The overall growth of males and females throughout the experiment is shown in Fig.5. lntermoult period
A comparison was made between the length of intermoult periods which preceded spawning and those which did not. In the first case eggs were developing and therefore using some of the prawns’ resources, whereas in the second more energy was available for somatic growth. The results showed that there was no correlation of intermoult period with length of the prawn except during part 1 in the case of females that were not producing eggs (Fig.@. In this,group the intermoult period increased proportionately with length.
167
l
s
.
. l
.
p-r ,._:.:::‘: . t
“; ; z -
20-
.
. 10 100
a,*
. .
l
.
l
.
.
I
I
110
120
TOTAL
-1 130 LENGTH
I
I
I
1
I
140
150
160
170
18C
b-m)
Fig. 6. The relation between intermoult period and length of female Macrobrachium rosenbergii that were not producing eggs, during part 1 of the experiment. The calculated regression line is drawn from the equation: Intermoult period = -2.82714 + 0.264996 total length (r = 0.321055, d.f. 51, 0.05 > P > 0.02)
The mean intermoult period during part 1 was significantly longer when eggs were being formed (38 days, s.e. 1.63, d.f. 43) than when they were not (31 days, s.e. 1.64, d.f. 60) (‘t’ test, P < 0.05). During part 2 prawns moulted at the same rate whether they were producing eggs (mean 43 days s.e. 2.799, d.f. 14) or not (mean 46 days, s.e. 3.200, d.f. 13). In the case of females that produced larvae the period between hatching of the eggs and the next moult varied between 9 and 37 days; it was longer (mean 34 days, s.e. 1.26, d.f. 3) when eggs were spawned at the following moult than when spawning did not occur (mean 16 days, s.e. 3.13, d.f. 5) (P < 0.05). The delay in moulting was thought to be associated with the development of oocytes in the ovaries. Spawning, incubation
and hatching
In Table II the number of times each female spawned and hatched larvae, and the total numbers of larvae produced by each female, are shown. One female did not spawn at all, eight others spawned once or twice but lost their eggs, and only 11 of the total number of 20 females produced live larvae. The mean number of broods from these 11 females lost following 37 of the total number of 68 was 2.82. Eggs-were spawnings. Three females spawned more than four times at successive moults and one produced larvae five times at successive moults. After the eggs were spawned they remained attached to the abdominal
168 TABLE II The spawning and larval production of Macrobrachium lasted 390 days Reference number of female
rosenbergii during an experiment
Total number of Spawnings
Hatches
Larvae
1 2 3
9 2 1
3 2 0
234 930 2 350 _
4 5 6
4 5 1
3 4 0
‘48 186 86 214 -
I 8 9 10
4 5 1 2
1 3 0 0
463 88 680 _ -
11 12 13 14 15
4 6 1 0 2
2 1 6 0 0
31560 6 360 166 630 _ _
16 17 18 19 20
6 5 1 1 2
3* 3 0 0 0
55 169 42 644 _ _ -
Totals
which
68
31
769 786
* The number of larvae in one of the broods was not determined
pleopods for an incubation period which lasted 19-22 days (mean 19.9 days, s.e. 0.134, d.f. 3 1) which is in agreement with the observations of John (1957) and Rao (1965). Eighteen of the broods hatched in one night, but 13 others took two nights to complete hatching (Table III). In the latter group there were no significant differences between the proportion of larvae in each brood that hatched on the first night (49%, range 6.9-92.8%) and those that hatched on the second (51%, range 7.2-93.1%) (P > 0.1). Similarly there were no significant differences in the mean lengths of larvae which hatched on the first and second nights (see Discussion). Samples of 20 larvae taken at random from each brood were measured and were between 1.9 and 2.1 mm (mean 2.0 mm) total length. In Fig.7 the experimental period is divided into consecutive 30 day intervals for which are shown the mean numbers of larvae per brood (line A), the total number of broods that hatched (line B), and the number of
169 TABLE III The number of larvae of Macrobrachium Reference number of female
First night Number of larvae
rosenbergii
that hatched on two successive nights
%
Second night Number of % larvae
First night Mean S.E. length
Second night Mean SE. length ~_.___
120 800 2 910 3 120 219
13.5 87.5 16.3 29.0 49.8
5 348 100 17 820 2 640 110
86.5 12.5 83.7 71.0 50.2
2.1 _ 2.1 2.1 2.1
0.007
2.1 _
0.006
0.013 0.009 0.009
2.1 2.1 2.0
0.008 0.008 0.010
33 600 20 560 18 800 8 244 70 852 1 714
52.1 18.5 92.8 28.5 83.7 6.9
64 500 4 410 1 360 28 914 11 548 25 739
41.9 21.5 1.2 71.5 16.3 93.1
_
Part 1 4 5 5 12 16 Part 2 1* 4 8* 13 13 17
1.9 1.9
_ 0.017 0.018
2.0 1.9 _
0.018 0.015
0.015
2.0 -
0.008
2.0 _
* Data for one brood not available (see Table 1).
100000 r
4” 10000
f----*
-
2 4
b
1000
-
n ii f
100 -
z
TIME
(30
DAY
P’ERI~OS)
Fig. 7. The mean number of larvae per brood (line A), the number of times spawning was successful (line B) and unsuccessful (line C) in an experiment with Macrobrachium rosenbergii reared in captivity.
170 times eggs were spawned but did not hatch (line C). For example, in the third 30 day period, which corresponds approximately to January 1971, 14 females spawned; of these, five retained their eggs and produced larvae. The mean number of larvae per brood was 2 600. Nine of the females lost their eggs before incubation was completed. The unproductive spawnings were more frequent than productive spawnings during the first seven periods, but after this time (May-June 197 1) the production of larvae was consistently higher and the number of unproductive spawnings was less than the productive (see Discussion). Males
Three males were used in this study and the number of times that mating was successful in each intermoult period is shown in Table IV. A successful mating resulted in viable larvae being produced by the female 20 days after copulation. The large proportion of matings that were unsuccessful during part 1 may have been due to adverse environmental conditions affecting either the males, the females or the eggs and their
I
1
‘40
,
1
!60
180 L,
I
200
I
220
(mm)
Fig. 8. Hiatt diagram (Hiatt, 1948) which shows the growth pattern of three male Mucrobrachium rosenbergii. The calculated regression line is drawn from the equation: Post-moult length = 3.2105 + 1.0557 pre-moult length (r = 0.8962, d.f. 15, P < 0.001)
171 TABLE IV The frequency with which each male Macrobrachium
rosenbergii mated in each intermoult
period _
Male tag
Length of intermoult period (days)
A
42 30 51 33 34 98
Number of successful matings
Total number of opportunities including successful matings 13 4 12 I 6 8
June 1971 25 Data incomplete B
26 49 36 38 45
June 1971 34 41 Data incomplete C
58 31 56 46
June 1971 Data incomplete
0
1
supporting membranes. It is not known why male C (Table IV) did not sire any larvae. The growth of the males is shown in Fig. 8. Growth was best described as arithmetic (although b = 1.056), since the standard error of b was sufficiently large to give 95% confidence limits of 0.8579- 1.2535, and because there was no significant correlation of increment and total length. There were no differences in the mean increments between individual males during either part of the exp.eriment. The combined data gave a mean length increment of 13.0 mm with 95% confidence limits of 9.23-16.77 mm, and this was similar to the mean increment (13.89 mm)
172
achieved by females during part 2. The mean intermoult period was 41.9 days (s.e. 9.89, d.f. 17) and was independent of the size of the prawn (Y= 0.04808, d.f. 16, P> 0.1). DISCUSSION
The reduced control of pH and photoperiod during the first 220 days (part 1) of the experiment may have produced a lasting effect on the reproductive potential of the prawns. The results show a distinct improvement in the reproductive ability of the animals after the environmental conditions were more constant. We consider that the control of photoperiod and pH exercised during part 2 of the experiment was beneficial to the prawns and, secondly, that the overall performance of the prawns (in terms of the number of larvae and broods produced per unit time) was improved. The first postulate is supported by the observed increase in mean brood size which occurred after 220 days and was maintained throughout part 2. Similarly, the number of times females spawned and lost their eggs, frequently after carrying them until eyespots had developed, was less in part 2 than in part 1. Our results compare favourably with those of Ling (1969), who reported that female M. rosenbergii kept in the laboratory were able to lay eggs twice within five months; he thought that they may be able to spawn 3-4 times in one year under natural conditions. In the experiment reported here eight females spawned two and three times, and one produced viable larvae four times, in the 170 days of part 2 of the experiment. The change in the environmental conditions may also have influenced the growth of the prawns. In parts 1 and 2 growth was arithmetic regardless of egg production, although in part 2 the mean length increment was larger (7.2 cf. 13.6 mm) (P < 0.05). The moulting frequency was very variable in all the four groups shown in Fig. 6, and the intermoult periods of females that were not producing eggs during part 1 increased with size. It should be noted that these females were mature (see below), since they produced eggs during other intermoult periods in part 1. In the other three groups there was no correlation of intermoult period with size and the mean intermoult periods did not differ significantly (P > 0.05). There was no evidence for progressive geometric growth and this possibly indicates that the smaller increments achieved at each moult in part 1 were a result of the less well controlled conditions. Kamiguchi (1971) found that the intermoult period of sexually immature Palaemon paucidens increased with size, but mature specimens moulted at approximately constant inter-
173
vals. His prawns also increased in length by a constant amount at each moult throughout the range studied (Kamiguchi, 1973, personal communication). Variations in the mean length of larvae from each brood also occurred, but there was no relation between larval size and either brood size or adult size. It might be expected, for example, that smaller larvae would hatch from the larger broods, due to less yolk being available for each egg or to the effects of physical crowding. No explanation is available for the significant positive correlation between larval size and adult size in the data from part 2. Some broods took two nights to complete hatching. Pandian and Katre ( 1972) found that the larvae of ~uc~o~~~c~~~~ idae Heller which hatched on the second night were 2% longer than those which hatched on the first night. Our larvae were too small (2 mm compared with the 5 mm of M: idae) for differences of this magnitude to be detected. Fecundity is usually determined by estimates of the number of eggs spawned by a given size group of females. The figure obtained in this way for caridean prawns is frequently higher than estimates of the number of live larvae produced, presumably because of mortality during incubation (Reeve, 1969). Rajyal~shmi ( 196 1) found the relationship between length and fecundity (expressed as the number of ova) in M. rosenbergii (Palaemon carcinus Fabr.) to be: log, ,, number of ova = -2.7949 + 3.3209 log, 0 female length (1) Our results were described by the equation: log, ,, number of larvae = 3.01036 -+3.34477 log, e female length (2) Eq. 1 may be solved to demonstrate that a 200 mm female produces 70 230 eggs and a 160 mm female produces 33 470 eggs; from eq. 2 the same sizes of female would give 48 530 and 23 010 larvae respectively, a difference of about 3 1%. It is not known if mortality during incubation is likely to be as high as this, and some of the difference probably results from the different populations that were studied.
Three male and 20 female prawns, ~acrobr~c~~~~ rosenbergii (de Man), were observed for 390 days. They were maintained in brackish water (5%0 salinity) at 28°C which was recycled continuously through a percolating biological filter. Illumination was artificial and did not exceed 10 lm/ft2 (approx. 0.1 m2 ) at the water surface. Mating readily occurred in the experimental tanks (48 x 28 x 25 cm deep). Eggs were incubated for 20 days; the mean number of larvae per brood was 24 000 (range 50-98 100). Over 750 000 larvae were hatched during the experiment.
174
Larger females had proportionately larger broods and larvae from seven broods were cultured to the post-larval stage at intervals throughout the experimental period, which demonstrated their viability. The increase in length of the adults at each moult was constant (arithmetic growth) and did not alter when ova were maturing in the ovary. Prawns achieved larger mean length increments after the environmental conditions were improved. The moulting frequency was very variable and, with one exception, did not change proportionately with length or age of the prawns. Females grew from 115 to 205 mm and males from 145 to 230 mm total length. Three females spawned more than four times in successive intermoult periods, and one produced viable larvae five times in succession. Two of the males sired viable larvae four and seven times respectively during one intermoult period. ACKNOWLEDGEMENTS
We acknowledge the assistance of Mr G. Williams in this work. REFERENCES Forster, J.R.M. and Wickins, J.F. (1972) Prawn culture in the United Kingdom: its status and potential. Lab. Leafl. Fish. Lab. Lowestoft, (New Series) No. 27, 32 pp. Hiatt, R.W. (1948) The biology of the lined shore crab Pachygrapsus crassipes Randall. Pacif Sci, 2,135-213.
John, C.M. (1957) Bionomics and life history of Macrobrachium rosenbergii (de Man). Bull. cent Res. Inst. Univ. Travancore, Ser. C, 5 (l), 93-102. Kamiguchi, Y. (1971) Studies on the molting in the freshwater prawn, Palaemon paucidens. I. Some endogenous and exogenous factors influencing the intermolt cycle. J. Fat. Sci Hokkaido Univ., Ser. VI, ZooL 18 (l), 15-23. Kurata, H. (1962) Studies on the age and growth of crustacea. Bull. Hokkaido reg. Fish. Res. Lab., No. 24, 1-115. Ling, SW. (1969) The general biology and development of Macrobrachium rosenbergii (de Man). Fish. Rep. F.A.O.,
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Pandian, T.J. and Katre, S. (1972) Effect of hatching time on larval mortality and survival of the prawn Macrobrachium idae. Mar. Biol., 13, 330-337. Rajyalaksmi, T. (1961) Studies on maturation and breeding in some estuarine palaemonid prawns. Proc. natn. Inst. Sci India, 27B (4), 179-188. Rao, R.M. (1965) Breeding behaviour in Macrobrachium rosenbergii (de Man). Fishery Technology, 2 (l), 19-25. Reeve, M.R. (1969) The laboratory culture of the prawn Paloemon serratus. Fishery Invest., Lond., Ser. 2, 26 (l), 38 pp. Wickins, J.F. (1972a) Developments in the laboratory culture of the common prawn Palaemon serratus Pennant. Fishery Invest., Lond, Ser. 2, 27 (4), 23 pp. Wickins, J.F. (1972b) Experiments on the culture of the spot prawn Pandalus plcltyceros Brandt and the giant freshwater prawn Macrobrachium rosenbergii (de Man). Fishery Invest., Land, Ser. 2, 27 (5), 23 pp.