Siganids: Their biology and mariculture potential

Aquaculture,

3 (1974)

325-354

@ Elsevier Scientific Publishing Company, Amsterdam

SIGANIDS:

THEIR

~ Printed in The Netherlands

BIOLOGY AND MARICULTURE

POTENTIAL

T.J. LAM Department

o,f Zoology,

University of Singapore (Singapore)

(Received January 14, 1974; revised March 27, 1974)

Siganids (rabbitfishes), which are .widely distributed in the Indo-Pacific, have recently attracted the attention of mariculturists in the Pacific and Israel. Research into siganid mariculture has been initiated in several countries. This paper lists the reasons behind the interest in siganid mariculture, and reviews: (1) what is currently known about the biology of siganids considered under (a) species identification, (b) fisheries, (c) ecology, (d) reproduction and early development and (e) behaviour; (2) problems requiring solutions before large-scale siganid mariculture can be realized; and (3) progress made to date in each area.

INTRODUCTION Siganids or rabbitfishes are a group of marine fishes belonging to the family Siganidae (Teuthididae) which are widely distributed in the IndoPacific region (Herre and Montalban, 1928; Fowler and Bean, 1929; De Beaufort and Chapman, 1951; Schultz et al., 1953; Fowler, 1959; Scott, 1959; Smith and Smith, 1963; Bini, 1965; Marshall, 1966; Okada, 1966; and others). Four species also occur in the Red Sea, two of which have migrated through the Suez Canal and are now established in the Eastern Mediterranean (Ben Tuvia, 1966). They are therefore a fairly cosmopolitan group of fishes. Herald (196 1) puts the number of siganid species known as 30; D.J. Woodland (personal communication) has seen only 20 valid species, although he believes there may be as many as 25. Many of these species are of economic importance where they occur. Siganids are now attracting the attention of mariculturists in many parts of the Indo-Pacific and in Israel. The reasons are as follows: (1) Siganids (or at least some species) are considered excellent food fish by many peoples in the Indo-Pacific and Eastern Mediterranean, particu-

326 larly in the Pacific Islands (Oceania). The fish is meaty and tasty, and chemical analysis of one siganid species (S. @VUS) shows a relatively high protein content (Peiris and Grero, 1972). The existing demand and market potential are high. (2) They are primarily herbivores in nature but may turn to other diets readily. Thus, in captivity they have been shown to feed on a wide variety of foods offered (see Food Habits). (3) During certain seasons large numbers of siganid fry can be collected from coastal waters (such as ‘grass’ or reef flats) for cultivation in coastal ponds, enclosures, tanks or floating cages. (4) Some (if not all) species are gregarious (schooling) and thus may be able to tolerate crowded conditions. (5) They appear to be tolerant of changes in salinity and temperature. This is at least true of Siganus canaliculutus (= S. orumin) (see Tolerance to Environmental Factors). (6) They appear to adapt well to captivity and grow rapidly on a diet of natural foods (algae or other plant materials) or artificial food pellets. (7) They can tolerate any type of pond soil, provided vegetation is present (Ablan and Rosario, 1962). (8) Some species traditionally have already been farmed (albeit on a small scale) in coastal ponds in The Philippines either in pure culture or, as is generally the case, with milkfish (Pillai, 1962). (9) Two species have been induced to spawn in captivity, both of which have even spawned spontaneously in captivity. Mature fish are available from nature for this purpose predictably at certain times of the year. Furthermore there is some evidence that siganids can mature in captivity (see Reproductive Cycle). (10) One species has been raised from eggs to adults in the laboratory in Japan, although in other species larval mortality remains a major problem. The mariculture potential of siganids was realized and recommended earlier (Ablan and Rosario, 1962; Catanaoan, 1965) but active and general interest has only developed very recently. In November 1972, a meeting of those interested in siganids and their mariculture was convened at the Hawaii Institute of Marine Biology. During the meeting, an informal Siganid Mariculture Group was formed. “Plans for a Siganid Fish Farming The Group produced a report, Program” which outlines recommended research activities and presents a tentative plan of organization, dividing tasks among participating institutions. The author is the Interim Coordinator for the Program. A report of the meeting was given by May (1973). It was thought that at this early stage of siganid mariculture efforts a review paper on what is currently known of siganids would be appropri-

327 ate. This paper will therefore review: (1) the available information on siganids and their biology, considered under the broad headings of (a) species identification, (b) fisheries, (c) ecology, (d) reproduction and early development and (e) behaviour; (2) the problem areas which need to be studied before siganid mariculture can acquire a firm footing; and (3) the progress made to date in each area. SPECIES IDENTIFICATION Siganids also are sometimes called teuthidids. However, Woodland (1972, 1973) has proposed to the International Commission on Zoological Nomenclature that the genudname Teuthis Linnaeus, 1766, be suppressed in favour of the genus name Siganus Forsskal, 1775. There is considerable confusion in the literature regarding identification of siganid species. Dr. D.J. Woodland of the University of New England, New South Wales, Australia, has begun to revise the family Siganidae. The species referred to in this paper follow Woodland’s suggested nomenclature (personal communication). In doing so, however, a number of species reported in the literature have had to be renamed. Thus Siganus oramin used by Manacop (1937) and Soh and Lam (1973) is now called S. canaliculatus. Woodland (personal communication) explains that the name canaliculatus Park 1797 has priority over oramin (Bloch and Schneider) 1801. According to him, two forms (or species) are consolidated here. In one form the spots above the lateral line are small (5 or 6 rows of pinhead-sized spots about l- 1.5 mm in maximum diameter) (Fig. 1 and 2). In the other form the spots above the lateral line are larger (3 rows of matchhead-sized spots about 2-3 mm in maximum diameter (Fig.3). The small-spot form also has smaller and more spots on the body. Both these forms occur in Singapore. However, it appears that only the small-spot form occurs in Palau. Similarly S. rostratus used by Tsuda and Bryan (1972) is renamed here as S. argenteus, and McVey’s (1972) S. fuscescens is actually S. canaliculatus (small-spot form). A list of some economically important siganid species in a few selected countries is given in Table I, based on Woodland’s nomenclature; some selected local names of the fishes, which may vary from region to region in the same country, are also given. FISHERIES In most places siganid fisheries are small, by commercial standards, important and well-established. This is perhaps due to two factors:

but (1)

328

Fig.l. Siganus canalicularus Park (small-spot form). The colour pattern is that of an alive greengrey background with small oval white spots and some scattered black spots or patches. This is the pattern assumed when the fish is among algae or ‘grass’ (Etzhalus sp.).

Fig.2. Siganus canaliculafus Park (small-spot form). The colour pattern here is that of a yellowishbrown (sand-coloured) background with distinct small oval white spots. This is the pattern assumed when the fish is over sand or a light background.

329

Fig.3. Fig.2.

Si@vzus cunaliculutus

Park

(large-spot

form).

Fig.4. Siganus guttatus Bloch. This fish is much

The colour

pattern

here

iS

larger than S. canaliculatus Park.

Shih

to

that

in

330 TABLE 1 Some economically important siganid species in a few selected countries. Species identification is based largely on D.J. Woodland’s nomenclature. The local names given are by no means complete since there may be many names for the same fish in the same country. (Information on Fiji, New Caledonia, New Hebrides and Solomons from D. Popper, personal communication, and that on The Philippines partly from I.A. Ronquillo, personal communication).

Country/ territory

Species

Local name

Figure/Plate

Palau

S. lineatus

Klsebuul

S. canaliculatus (small-spot form; = S. oramin)

Meyas

Col. Pl. 50, Fig. 335 (Marshall, 1966); Pl. VII, Fig. 2 (Halstead, 1967b). Figs. 1 and 2 (this paper)

S. spinus

Fry: Manahac Hatang; Adult: Sesjun Fry: Manahac Leso; Adult: Sesjun

Pi. VII, Fig. 4 (Halstead, 1967b; Pl. 73 (Schultz et al., 1953) Pl. 35C (Smith and Smith, 1963); PI. 74 (Schultz et al., 1953)

S. argenteus (= S. rostratus) Fiji

New Caledonia

New Hebrides and Solomons The Philippines

S. vermiculatus S. punctatus S. doliatus S. spinus S. argenteus (= S. rostratusj

Nuqa ni veidogo Nuqa ni cakau Nuqa ni cakau Nuqa mulu

PI. IX, Fig. 2 (Halstead, 1967b) see above references see above references

S. canaliculatus (= S. oramin) S. lineatus S. argenteus (= S. rostratus) S. punctatus S. doliatus

Figs. 1, 2 and 3 (this paper)

S. canaliculatus (= S. oramin) S. lineatus

Figs. 1, 2 and 3 (this paper)

S. canaliculatus (= S. oramin) S. vermiculatus S. guttatus S. fuscescens S. virgata S. striolata (= S. spinus? ) [Siganid fry]

see above references see above references see above references

see above references Barangen; Titang; Dangit

Figs. 1,

Malaga Batawayi; Dangit; Layap Mandalada

Fig. 4 (this paper) Pl. VII, Fig. 1 (Halstead, 1967b).

Kuyog; Padas

4 and 3 (this paper)

331 _ Country/ territory Singapore Malaysia

and

Species

Local name

Figure/Plate

S. canaliculatus (both small-spot and large-spot forms; = S. oramin) S. guttatus

Peh-Tor Dengkis

Figs. 1, 2 and 3 (this paper)

S. jaws

Israel and Eastern Mediteranean

S. rivulatus

(Chinese); (Malay)

Wuay Tiam (Chinese); Dengkis (Malay) Tee-Qui (Chinese); Dengkis, Debam (Malay)

Fig. 4 (this paper)

Sikkan; Black Spine-foot (Israel);

Fig. 1 (Ben-Tuvia, 1966); PI. 47, Fig. 334 (Marshall, 1966)

Fig. 5 (this paper)

Agriosalpa (Greece); Sigano (Italy); Qawsalla (Malta); Carpan (Turkey) S. luridus

Fig. 2 (Ben-Tuvia,

1966)

Japan

S. fuscescens

Aigo; Ae

(Okada, 1966); PI. VII, Fig. 1 (Halstead, 1967b).

Hong Kong

S. fuscescens

Lai Maan

See above references

Sri Lanka (Ceylon)

S. jaws

Nava; Orava

Fig. 5 (this paper)

Fig.5

Siganus jaws Linnaeus

332

seasonal nature of the catch and (2) relative difficulty of catching adult siganids on a large, commercial scale because of their habitats and behaviour. However, in Palau, siganids form a major fishery; an estimated 500 metric tons of siganids are caught, constituting an average of some 27% of the fish landed at the Palau Fishermen’s Co-operative (Helfman, 1968). Adults

Adult siganids are caught mainly on a seasonal basis (e.g., during the spawning runs) by a variety of indigenous fishing gear (mainly traps) and methods (particularly spearing). In Singapore, S. cunaliculatus (= oramin) is caught in ‘kelong’ (large palisade fish traps), by ‘bubu’ (portable basket-traps) placed in reef and Enhalus flats, and by means of seining along Enhalus beds at low tide. Descriptions of ‘kelong’ and ‘bubu’ are given by Burdon and Parry ( 1954). The siganids caught are sometimes cooked whole in boiling salt water and sold in this form in the market. The fish is said to be better preserved by this means. In The Philippines, siganids (‘barangen’) are caught by fish traps simple speargun (‘bobo’, ‘nasa’ or ‘pasabing’), fish corrals (‘baklad’), (‘pana’), or by hook and line (Catanaoan, 1965; I.A. Ronquillo, personal communication). The fish are sometimes made into ‘pindang’, fillets salted and dried in the sun. A good account of the siganid fishing techniques in Palau is given by Helfman (1968) and Drew (1971). Briefly, the siganids (mainly S. lineatus) are speared individually after they have been impounded by approp.riate nets in an area of the reef or grass flat that is exposed at low tide. This type of fishing is most successful at night when the fish can be immobilized by a flashlight beam (Helfman, 1968). Similarly, in Guam siganids are collected by spearing (R.T. Tsuda, personal communication). In Israel, siganids are mostly caught in traps (made of chicken wire and set in depths of 2-20 meters) in Eilat and by gill-nets and trammel-nets on the Mediterranean coast (Ben-Tuvia et al., 1973). Juveniles

Juvenile siganids (fry) are much more easily collected than adults because of their abundance in certain seasons. At present, the only fishery that exists for these fry is in The Philippines. There they are caught in shallow and deep waters by beach seine (‘karokod’), push net, lift net and round haul seine; the latter two nets are used with incandescent lights to

333 attract the fry (Ablan and Rosario, 1961, 1962). The fry (‘padas’) are utilized for making ‘bagoong’ by the local fishermen. According to LA. Ronquillo (Chief, Marine Fisheries, The Philippines, personal communication), ‘bagoong’ is a fish paste obtained by fermentation of properly salted whole or ground fish in which the siganid fry is one of the raw materials. “It has a flavor similar to anchovy paste prepared in Europe” and is commonly used in The Philippines “as a condiment or flavoring agent for vegetables and meat.” Besides ‘bagoong’, “a liquid fish .sauce known as ‘patis’ is often made by separating the solid from the liquid portion of the autolysate.” The sauce “has a characteristic cheese flavor and fish odor.” This practice, however, is wasteful; the fry could be better utilized for mariculture (Ablan and Rosario, 1962).

ECOLOGY

The ecology of siganids has been little studied. Much of the available information is based on field observations and information from fishermen. The food habits of the fish are the only aspect which has received considerable attention.

Habitat

In general siganids’often occur in large schools, on and around ‘grass’ or reef flats. They may also be found in mangrove or harbour areas (see Table II). Some species (es., S. guttutus and S. vermicu2utus) may even enter rivers and lakes. In certain areas (e.g., Singapore and The Philippines), siganids seem to disappear from the usual habitats during certain times of the year. In The Philippines, the appearance and disappearance of siganids seem to be related ‘to the lunar cycle (I.A. Ronquillo, personal communication).

Tolerance to environmental

factors

factors has been studied in S. canaliculutus. of a fairly wide range of changes in salinity and temperature. The fish can withstand direct transfer to at least one-third sea water and seems to thrive in this medium and in 50% sea water. It can be acclimated gradually to live in low salinities (down to 5%0 ). The fish has been maintained in open tanks where the temperature of the water may vary from 25 to 34°C. This tolerance to salinity and temperature changes is also indicated by the fact that the fish occurs on ‘grass’ flats where the salinity fluctuates from 17 to 37%0, and the temTolerance

to environmental

Our studies show that the fish is tolerant

334 TABLE II Habitats of some siganid species

Species

Habitats

References

S. canaliculatus

‘Grass’ (mostly Enhalus spp.) flats mainly; also found on reef flats and among mangroves.

Soh and Lam, 1973; Lavina and Alcala, 1973; Drew, 1971.

S. lineatus

Reef flats Along docks and on ‘grass’ flats; juveniles seem to prefer mangroves.

D.J. Woodland, personal communication; Drew, 197 1.

S. spinus S. argenteus

Reef flats; harbours; seem to prefer areas of fairly brackish and turbid water. Juveniles invade reef flats seasonally. S. spinus is found where there are some coral growths but usually not where the growths are heavy.

Tsuda and Bryan, 1975

Schultz et al., 1953.

S. rivulatus

‘Grass’ Rats (Halophila sp.) Shallow water in harbour; semienclosed rocky pools.

G.W. Kiss& personal communication; Ben-Tuvia et al., 1973.

S. fuscescens

Reef flats Well-vegetated bottoms of shallow waters. Coastal waters; they choke water intakes (for cooling purposes) from time to time in Hong Kong.

D.J. Woodland, personal communication; Okada, 1966; E.H. Nichols, personal communication.

S. guttatus

Coastal, but seem to enter and leave rivers with the tides.

C.L. Soh and T.J. Lam, unpublished observations; Herre, 1953.

S. javus

Marine, brackish and fresh water. May enter rivers and lakes.

De Beaufort and Chapman, 195 1 Herre, 1953.

S. virgata

Around coral reefs

Herre and Montalban, 1928; CL. Soh and T.J. Lam, unpublished observations.

S. vermiculatus

Marine, brackish and fresh water. Often enter rivers.

De Beaufort and Chapman, 1951; Herre, 1953.

perature

from 23 to 36°C (Drew,

1971). However,

we have found that S.

cunalicuZutu~ is sensitive to O2 deficiency and high pH values (>9). In another study, S. canuliculutus was acclimated successfully to 40% sea water (about 14%0 salinity) but did not tolerate well a medium of 25% sea water (8.75%0 salinity) (Lavina and Alcala, 1973). The latter observation seems contrary to our own. However, Lavina and Alcala (1973) found that the fish did not tolerate O2 concentrations below 2 ppm, which is consistent with our observations.

335

Ben-Tuvia et al. (1973) have observed that S. rivulatus and S. luridus are tolerant of rough handling, overcrowding, and oxygen deficiency and can be transferred easily in small containers. Their ability to withstand large changes in temperature and salinity is indicated by the fact that they have passed through the Suez Canal from the Red Sea and are now well established in the eastern Mediterranean (Ben-Tuvia, 1966). However, Pillai (1962) suggests that siganids (species not specified) may not tolerate low salinities and high temperatures. Food habits

A number of studies have been made on the food habits of siganids (Suyehiro, 1942; Hiatt and Strasburg, 1960; Okada, 1966; Jones, 1968; Helfman, 1968; Drew, 1971; Tsuda and Bryan, 1973). They have all shown that siganids, both juveniles and adults, are primarily herbivores; this is also reflected in the dentition and gut morphology of the fishes: mouth small, numerous small, conical teeth in each jaw, pharyngeal teeth well developed; stomach rather thick-walled; intestine broad, extremely long, coiled, and thick-walled (Suyehiro, 1942; Hiatt and Strasburg, 1960; Tominaga, 1969). The larval fishes, however, are most likely plankton feeders. A detailed analysis of the stomach contents in adult Siganus spinus has been made by Jones (1968). His data show that S. spinus is a roving herbivore browsing on a relatively narrow range of benthic algae including the following genera: Padina, Cladophoropsis, Gelidium, Hypnea, Dictyota, Sphacelaria, Ectocarpus and Jania. Some thirteen other genera were also observed but they were considered insignificant in the diet. Tsuda and Bryan ( 1973) studied the food preference of juvenile Siganus argenteus (= S. rostratus) and S. spinus in Guam. They found that ( 1) only 10 of the 45 common genera of reef algae tested were eaten by both species; (2) both species fed preferentially on filamentous algae but did not eat blue-green and noncalcareous fleshy algae; (3) there were differences in food preference between the two species; Chlorodesmis fastigiatq was avoided by S. spinus but devoured by S. argenteus (= S. rostratus), while Polysiphonia sp. was rejected by S. argenteus but eaten by S. spinus; (4) both species would eat only one genus at a time and would begin feeding on the next preferred alga only after the first alga was completely consumed; (5) the order of preference was similar for both species: (i) Enteromorpha, (ii) Feldmannia and Derbesia, and (iii) Cladophoropsis. Comparison with Jones’ (1968) work on adult S. spinus (above) shows that the food preference of juveniles and adults is similar. There is evidence, however, indicating that siganids are not obligatory

336 herbivores. Hiatt and Strasburg (1960) have found 5’. urger&us in the vicinity of garbage dumps where it consumes waste meat scraps. In Palau, Klsebuul (S. Eineatus) are often found with large amounts of sponge in their stomachs and intestines, and meyas (S. canaliculatus) are frequently caught from docks with small hooks baited with fish scrap (Helfman, 1968). In studies of stomach contents of siganids, animal matter is sometimes found admixed with algae. Ingested animal material has contained amphipods and copepods (Jones, 1968), sponges (Drew, 197 1), foraminiferans (Hiatt and Strasburg, 1960), fish larvae, crustacean larvae and siliceous spicules (Lavina and Alcala, 1973) although all of these items may be considered incidental. In captivity, S. canaliculatus (= oramin) has been shown to feed readily on all kinds of food offered, such as Enhalus sp. (‘eel grass’), tapioca leaves, grass, Hydrilla sp. (freshwater aquatic plant), chicken food pellets, cooked rice, dried shrimps and even fish scraps (Fig.6) of their own species (T.J. Lam and C.L. Soh, unpublished data), algae, unsalted crackers and pieces of tuna (Drew, 1971). In fact when the non-plant food items are present, the fish shows no interest in any algae or other plant materials placed in the tank (personal observations; Drew, 197 1). Similarly, 5’. rivulatus kept in aquaria will feed on a variety of foodstuffs such as chopped fish or molluscs, fish meal, pellets, seaweeds and lettuce (BenTuvia, 1971; Ben-Tuvia et al., 1973). Thus siganids are potentially omnivorous even though they may be primarily herbivorous in nature.

Fig.6.

Dead S. canaliculatus

showing

pats

eaten

away

by other

members

of the school (arrowed).

337 Growth

There is some information in the literature on growth of siganids in nature. In southern Negros (The Philippines) S. canaliculatus grows to a mean standard length of 8 cm in about three months, 10 cm in about four and a half months, and 14 cm in about seven or eight months (Lavina and Alcala, 1973). In Singapore, S. canakulatus grows to about 120 grams in about 9-l 1 months, while in the Mediterranean, S. rivulatus grows to about 150 grams at the end of its first year (Ben-Tuvia et al., 1973). In Palau, preliminary studies suggested that juvenile S. lineatus can grow at a rate of 14 mm a month in an “enriched” dockside area and about 3 mm a month in a more natural mahgrove area (Drew, 197 1).

Spawning seasons and grounds

From available information to date, it would appear that most siganids have a definite spawning season (Table III), although it may be more marked in some species than in others. It is interesting that a species like S. canaliculatus, which occurs in the tropics, should have a marked spawning season. This season is remarkably similar in three different regions of the Pacific where the fish occurs, although the season in Palau appears to be slightly later. However, Drew (197 1) has observed large TABLE

III

Spawning

seasons

in some siganids

Species

Spawning

S. canaliculatus (= S. oramin)

Singapore: January-April (peak in February-March); possibly a second but minor season in July-October

C.L. Soh and T.J. Lam (unpublished data)

The Philippines: January-April in some areas; January-February in others; possibly a second season in July-September

Manacop (1937); Lavina and Alcala (1973)

Palau: February-June (peak in AprilMay); possibly a second season in October-December

McVey (1972); Drew (1971)

S. fuscescens

July-August

Okada

S. rivulatus

Late spring and early summer (presumably May-July)

H.W. Kissil (personal communication)

S. lineatus

February-March and around August (?) or various times of the

Drew (1971)

year (7)

seasons

References

(1966)

338 numbers of S. canaliculatus juveniles in March-April in Palau, which would put the spawning season closer to those in Singapore and The Philippines. There appears to be a second but minor spawning season for S. canaliculatus. In Singapore waters, the juveniles appear not only in FebruaryMay but also in August-October though to a lesser extent. However, ripe fish have not been obtained either prior to or during the second period. Similarly, in The Philippines, the fry appear for a second season in August and September (Lavina and Alcala, 1973). And in Palau, Drew ( 197 1) has also observed large numbers of juveniles (presumably S. canaliculatus) a second time in November-December. Nevertheless, direct evidence of a second spawning season for S. canaliculatus is lacking and the possibility exists that the juveniles observed belong to another species. Information on spawning grounds of siganids is scanty. Manacop (1937) reported that in The Philippines, Amphacanthus oramin (presumably = S, canaliculatus) lays eggs on the bottom in shallow waters, especially in and around fish corrals. In Palau, S. canaliculatus is said to spawn in the surf zone of the outer reef (Helfman, 1968; McVey, 1972) and ‘klsebuul’ (S. lineatus) is suspected to spawn near mangroves (Drew, 197 1).

REPRODUCTION

AND EARLY DEVELOPMENT

Sexual dimorphism Sexual dimorphism in siganids was reported by Helfman (1968). The male is said to have a slightly more elongated body’than the female. However, our measurements of depth in relation to length in S. canaliculatus revealed neither a statistically significant difference nor an apparent difference between the sexes. We tend to agree more with Manacop (1937) who wrote: “The dangit [probably S. canaliculatus] are not sexually dimorphic; nevertheless, during the breeding season the sexes may be readily distinguished and separated by the following criteria: (1) The males are generally smaller than the females . . . (2) The abdominal region of the females is more distinctly plump and enlarged than that of the male on account of the ripening ovary. (3) The genital aperture of the female is more enlarged than that of the male for the free passage of the ripe eggs. (4) When slight pressure is applied on the vent region, ripe, orangecolored eggs come out from the female and white milt from the male. (5) In the water the female is less active than the male because of the weight of the ripe eggs.”

339 Size at maturity Manacop (1937) gave the sizes (probably standard lengths) of mature Amphacanthus oramin (probably S.canaliculatus) as 11-14 cm for males and 13-2 1 cm for females. Our data tend to agree with his although mature males larger than 14 cm standard length have also been recorded. Helfman (1968) has similarly recorded a standard length of 13 cm and longer for S. canaliculatus females found to have maturing eggs. For S. lineatus, Drew (1971) gave the average minimum size of ripe females as about 22 cm standard length. However, Helfman (1968) has observed maturing eggs in S, lineatus 14 cm standard length and larger. Reproductive cycle We have made a study of the reproductive cycle of S. canaliculatus (C.L. Soh and T.J. Lam, unpublished data). The cycle is an annual one. Juveniles appear during the spawning season (peak, March-April). These will grow rapidly to adult size by December after which the gonads begin to mature rapidly, attaining full maturity by late January of February. Spawning follows until April. The spent fish seem to disappear thereafter. It is possible that the fish die after spawning. However, no direct evidence exists and at least some may survive spawning because exceptionally large fish (> 180 g), which we believe to be more than one year old, are sometimes collected. A similar cycle has been reported for S. canaliculatus in The Philippines and subsequent gonadal cycles have been observed (Lavina and Alcala, 1973). We have observed that the fish can indeed mature in captivity given favourable environmental conditions and sufficient food. Similar observations have been made by McVey (1972) and Popper et al. (1973) for S. canaliculatus and S. rivulatus, respectively. In fact, we have evidence to indicate that S. canaliculatus can mature in captivity earlier than in nature (T.J. Lam and C.L. Soh, unpublished data). Most of the males maintained in our tanks (low nitrite level; pH 7.8 + 0.1; temperature 26630°C; adequate aeration and circulation; fish fed chicken food pellets) since July were fully mature (milt expressed on gentle pressure on abdomen) by October-November, at least two months ahead of nature. However, only some females showed maturing eggs at this time. Thus the male appears to mature earlier than the female. However, we also have evidence to show that under certain stressful conditions gonad regression occurs in S. canaliculatus. This happened when gravid females were brought back from nature and kept in small

340 earthern jars without filtration or other means of controlling water conditions; the fish did not appear to feed under these circumstances (Soh and Lam, 1973). Similarly gonad regression appeared to occur when water conditions in a tank of fish, maintained for some time, deteriorated due to excessive growth of algae in increased sunlight. Before this change occurred the fish were less wary, coming voraciously for the food as soon as and whenever food was given, and most of the males were found to be milting. After the change, however, the fish became extremely wary? hiding in corners and among the algae most of the time, and would not come for the food when food was given. After one month under these conditions, none of the males was found to be milting. Thus it appears that proper environmental conditions and food are essential for the maturation of the fish. It is possible that when environmental conditions are favourable, food is an important factor which influences the maturation rate of the fish. Spawning Spawning of Arnphacanthus oramin (presumably S. canuliculatus) was studied by Manacop ( 1937) in The Philippines. It occurs from the fourth to the seventh*night after the appearance of the new moon during the spawning season (Table III) in some areas, and from the fifth to the sixth night of the new moon in other areas. “The fish come in large schools to shallow tidal flats as the tide begins to rise, and spawning begins after midnight, when the tide begins to recede, and lasts until dawn.” In Palau, S. canaliculatus spawns five to seven days after the new moon during the spawning season (McVey, 1972). The fish has been induced to spawn spontaneously in captivity (McVey, 1972). When the ripe fish were transferred from 3 ft of water (0.9 m) in a circular tank to 7-9 in of water (18-23 cm) in a flat, rectangular tank, spawning began immediately. “Females would nudge the abdomen of males to encourage release of milt and as soon as the males responded the females would release their eggs.” Apparently the fish would depend on wave action for mixing the eggs and sperm together. Natural spawning in captivity has also been achieved for S. rivulatus (Popper et al., 1973). When the water in the aquarium (2 m3) in which mature fish had been kept for two weeks was “changed to fresh sea water”, spawning occurred 10 h later. It would appear from this and McVey’s (1972) work that some form of environmental change (probably a fall in water level) is needed to stimulate spawning in siganids. In this connection, it is interesting to recall from the above-mentioned report by Manacop (1937) that 5’. canaliculatus (? ) spawns when the tide begins to recede.

341 Fecundity S. cunaliculutus (? ) was reported to deposit from 300 000 to 400 000 eggs at one spawning (Manacop, 1937). Our estimation of the number of eggs in the ovary of S. carzaliculatus gives similar figures (300 OOO500 000).

Early development

The early development of siganids has been studied in three species: S. fuscescens (Fujita and Ueno, 1954; Uchida et al., 1958; Okada, 1966), S. canaliculatus (= S. oramin)‘(Manacop, 1937; McVey, 1972; Soh and Lam, 1973), and S. rivulutus (Popper et al., 1973). It appears similar to that of other teleosts. A comparison of some aspects of the early development of the three species is given in Table IV. In general the ripe eggs of siganids are small, transparent, colourless, spherical, demersal and adhesive, and contain oil globules. Hatching time is variable, depending on temperature and perhaps on the species and locality. The larvae of S. canaliculutus are very small, those of S. fusccscells are larger, and the larvae of S. rivulutus are intermediate in size. The behaviour of the larvae is described by McVey (1972) and Popper et al. (1973). The larvae appear to be attracted by light (Soh and Lam. 1973; Popper et .al., 1973). In most cases the larvae did not survive much beyond the time of yolk absorption. This has been attributed to a lack of proper food for the larvae. However, larvae of advanced development have been described for S. fuscescens (Uchida et al., 1958; Okada. 1966). BEHAVIOUR

A good account of the behaviour of S. lirleatus and S. canaliculatus has been given by Drew (197 1 ), and Okuno (1963 ) has described the social behaviour of S. fuscescens. From these accounts and our own observations of S. cunaliculutus, the following may be said of the behaviour of siganids (or at least some siganids) in general. (1) They are gregarious, swimming and feeding in schools whose size seems to vary not only among species but also among schools of the same species. However, when conditions are unfavourable and the fish are under stress, S. canaliculatus has been observed to become territorial, each individual defending a specific area and chasing off approaching intruders. (2) They are wary and appear easily frightened, the juveniles perhaps less so than the adults.

S. rivulatus

Demersal, adhesive, with 4-7 large oil globules and several small ones

Transparent colour\ss

S. fuscescens

Spherical

Demersal, adhesive, with more than 10 large oil globules and many small ones

Spherical

Transparent yolk

Adhesive, with oil globules

Demersal, adhesive

Other features

S. fuscescens

Spherical

Spherical

Shape

Demersal; a few floating

Transparent colourless

Translucent orange

Colour

Ovulated or ripe eggs

S. canalicdatus (wrongly identified as S. fuscescens)

S. canalicuhtus (= S. oramin)

canaliculatus)

(probably = 5.

Amphacanthus oramin

Species

0.620.66

0.60

0.53

0.420.46

0.70

Size (mm)

Comparison of some aspects of early development in three siganid species

TABLE IV

-

at 25.5-27°C: 30 (fish from Mediterranean); 29.5-31.5 (fish from Red Sea)

27 at 23.5-26°C

28 at 31°C

30-35 at 25-27°C

62 at 27.5”C

Hatching time (h after fertilization)

1.8 (Mediterranean fish) 1.8-2.3 (Red Sea fish)

2.60

0.76-1.27 (0.03-0.05”)

1.55

1.50

Larva size at hatching (mm)

98

75

64-68

72

Time of complete or almost complete yolk absorption (h after fertilization)

Popper et al., 1973

Fujita and Ueno, 1954; Uchida et al., 1958

Okada, 1966

McVey, 1972

Soh and Lam, 1973

Manacop, 1937

References

8

W

343

Fig.7. S. canaliculatus

Fig.8. S. canaliculatus

showing

in fright

a colour

colour

pattern

pattern.

that blends effectively

with the background.

344 (3) They are capable of rapid colour changes and show remarkable camouflage ability. Some of the colour patterns of S. cunaliculutus are given in Figs. 1, 2, 3, 7 and 8 (see figure legends for explanation). (4) They seem to be attracted by diffuse light, particularly the juveniles. They may be immobilized at night, particularly the adults, by shining a flashlight directly upon them. In fact this is the means we employ to catch the wary S. cunaliculatus in our tanks.

PROBLEM

AREAS

AND

PROGRESS

TO DATE

The Siganid Mariculture Group has identified five main problems and one subsidiary problem as areas requiring active research before siganid mariculture can be fully realized. These are (1) a species survey, (2) juvenile-to-adult farming, (3) fry production, (4) production economics, (5) spine irritation (fin spines possess venom) and ciguatera (gastrointestinalneurological problems associated occasionally with ingestion of some fishes), and (6) transportation techniques (see “Plans for a Siganid Fish Farming Program” by the Siganid Mariculture Group)*. To these may be added the problem of disease, although it is actually part of problem (2). In this paper, each of these problem areas will be discussed, briefly, in turn, together with an account of the progress made to date.

Species survey

The data presented previously is a start toward this requirement (Table I). The survey should be expanded to include other regions and countries. Further data on identification including common names and photographs of specimens should be obtained. In addition, a market survey should be conducted to identify factors affecting the market value and acceptance of various species in the different regions - such as palatability and abundance - in order to pr0vide.a rational basis for selection of species to be cultured. Juvenile-to-adult

farming

As noted before, juvenile siganids (fry) often occur in great abundance during certain seasons, and they may be collected easily at these times. At present they are not being utilized in many regions. In fact they are being regarded as a nuisance by fishermen in the Singapore-Malaysian region because the fishermen catch large numbers of them unintentionally and *Copica available

from the author

on request

345 have no use for them. In The Philippines, as mentioned earlier, the juveniles are utilized for producing fermentation products. These juveniles could be utilized profitably or better utilized for mariculture. They could be reared to marketable size in suitably designed holding structures such as ponds, tanks or enclosures in natural areas and in floating cage nets. These suggestions are thought to represent the best immediate prospect for the initiation of commercial farming of siganids. Development of efficient and economical foods and the design of suitable holding structures are important related research needs. The progress made to date in the farming of juvenile siganids may be categorized into: (a) collection, (b) transportation, (c) food habits and (d) culture. (a) Collection. The seasons and places of occurrence of juvenile siganids are known in many regions. The juveniles appear during and immediately following the spawning seasons and are found predominantly on or around “grass” or reef flats. In some areas the actual time of their appearance can be accurately predicted. Thus, in Guam the juveniles of 5’. urgenteus and S. spinus occur plus or minus two days of the third-quarter moon during the months of April and May, and occasionally during June and October (Tsuda and Bryan, 1973). Similarly, in The Philippines juvenile siganids (“padas”) predictably appear on or before the new moon during the months of February, March and April (I.A. Ronquillo, personal communication). The juveniles have been collected alive by various means such as the push-net, scoop or dip net, seines, throw nets and lift nets (Ablan and Rosario, 1961, 1962; Drew, 1971; Ben-Tuvia et al., 1973; C.L. Soh and T.J. Lam, unpublished data). Artificial light is sometimes used to attract the fish at night during collection (Ablan and Rosario, 1962; Ben-Tuvia et al., 1973). Three methods of collection used in The Philippines have been described in considerable detail by Ablan and Rosario (1962) and Pillai (1962). (b) Transportation. Siganid fry have been transported alive successfully from the place of capture to the place of culture (tanks, cage-nets, or ponds). While some species (e.g. S. canaliculutus) require care in handling during transit (Ablan and Rosario, 1962; Pillai, 1962; C.L. Soh and T.J. Lam, unpublished data), other species (e.g. S. rivulutus) seem to be tolerant of rough handling and may be transferred easily in small eontainers (Ben-Tuvia et al., 1973). A good account of the transportation techniques used in The Philippines has been given by Ablan and Rosario (1962) and Pillai (1962). To ensure success, Ablan and Rosario (1962) have given the following points: “( 1) Keep the fry always under water. Never expose them to atmospheric air.

346

(2) Fill empty containers (e.g., earthenware jars) with clean and clear sea water to a half full capacity before the necessary number of fry is accommodated. (3) Eliminate the undesirable species to insure maximum oxygen while the fish are in the containers. (4) Scoop and transfer fry cautiously with a porcelain cup or bowl to minimize struggling to maintain vitality. (5) Maintain the maximum amount of water the containers can hold. (6) Fry should be given proper aeration by simply removing some water and adding the same quantity of water from the sea, a process repeated until the destination is reached.” (We have successfully used aeration with an air pump.) (c) Food habits. The food habits of juvenile siganids in nature and in captivity have been investigated including their preferences (see Food habits, p.335). (d) Culture. Attempts have been made in several countries to culture juvenile siganids in (i) tanks; (ii) floating cage-nets or pens and (iii) coastal ponds. The results of all studies but one have been most encouraging. (i) Tanks. In Israel, S. rivulatus fry maintained in aquaria (2 15 x 67 x 10 cm) and fed with algae (UZva sp.) and commercial fish food pellets (25% proteins) showed a tenfold increase in weight and a twofold increase in length after 39 days. Fish fed with lettuce also grew well but at a slower rate than those fed with fish’ pellets (Ben-Tuvia, 1971; Ben-Tuvia et al., 1973). Similar results have been obtained for “padas” (unidentified siganid fry) in The Philippines fed with algae (Ablan and Rosario, 1961) and for S, canaliculatus in Palau fed with trout chow (McVey, 1972) and in Singapore fed with commercial chicken food pellets (C.L. Soh and T.J. Lam, unpublished data). Further experiments in Israel showed that multiple feeding each day produced better growth in S. rivulatus than feeding the same quantity of food once each day (Kiss& 1972). (ii) Floating cage-nets. Some experiments on floating cage-net culture of S. rivulatus fry have been conducted in Israel (Kissil, 1972). The results showed that (1) the fish grew much faster in floating cage-nets than in tanks, some attaining a weight of 185 g in a total of 300 days; (2) food conversion ratios at a 6% feeding rate were between 2 : 1 and 4 : 1; (3) a combination of fish scraps and pellets might be as effective a food as fish pellets alone, although fish scraps alone we,ie inadequate; and (4) pelletfed fish were in better condition than naturally occurring fish. Similarly, encouraging results have been obtained for S. canalicukztus in Palau (McVey, 1972). The fish showed good growth in floating pens, and those in pens located where there was good water circulation grew faster

347

than those in pens located where water circulation was poor. Also, better growth was obtained with trout chow than with algae alone. (iii) Coastal ponds. Certain species of siganids (esp. S. vermiculutus) are already farmed either in pure culture or, as is generally the case, with milkfish in coastal ponds in The Philippines (Pillai, 1962). The siganids attain a marketable size within five to seven months. Pillai (1962) gives a good account of the farming methods used. An attempt to culture S. canaliculatus (= S. orumin) fry in a marine fishpond at Lucap (The Philippines) also yielded good results. However, the same species has been shown not to be a good candidate for pond culture in southern Negros (The Philippines) where the marine fish-ponds show great fluctuations in environmental conditions (Lavina and Alcala, 1973). The problem appears to lie in the fish’s intolerance to low oxygen concentrations (below 2 ppm). Fry production

Although fry collection from nature may be relied upon to initiate siganid mariculture, research on fry production must be carried out concurrently, in the long-term view, to ensure a steady year-round supply of fry for the stocking of commercial farming operations. The research involves (a) natural spawning in captivity, (b) induced spawning, (c) larval rearing, (d) induced gonadal maturation and (e) hybridization. (a) Natural spawning in captivity. As mentioned earlier, natural spawning in captivity has been achieved in two species, S. canaliculatus and S. rivuhtus. (b) Induced spawning. S. canaliculatus has been induced to ovulate or spermiate using human chorionic gonadotropin (HCG), followed by successful artificial fertilization (Soh and Lam, 1973). Stripping and artificial fertilization have also been achieved in fully ripe S. canaliculatus and S. rivulatus without hormone treatment (Manacop, 1937; Popper et al., 1973). (c) Larval rearing. This appears to be the main problem in fry production. Attempts to rear larvae of S. canaliculatus and S. rivulatus have so far met with little success (McVey, 1972; Soh and Lam, 1973; Popper et al., 1973). The problem appears to lie in finding the right food for the larvae. However, Harada has succeeded in rearing S. fuscescens larvae to marketable size; the larvae, which are bigger than those of S. canaliculutus or of S. rivulutus (Table IV), were fed wild plankton (P.T. Wilson, personal communication). (d) Induced gonadal maturation. Mature fish are necessary for induced

348

or natural spawning, but they are available only on a seasonal basis. Thus in order to produce larvae on a year-round basis, the fish must be induced to mature outside the normal breeding season(s). Research is underway in our laboratory to identify environmental factors conducive to gonadal maturation in S. canaliculatus. Good water conditions and food appear to be important, but long photoperiod (18 h light) seems to retard maturation (T.J. Lam and C.L. Soh, unpublished data). The effects of salinity and temperature are now under study. (e) Hybridization. Since artificial fertilization does not seem to be a problem with siganids, hybridization may be attempted to improve the quality of the fish, particularly when there are several species of siganids in each region. For example, it would be interesting to hybridize S. curzaliculatus (Figs. 1, 2 and 3) with the much larger but less palatable S. guttutus (Fig. 4) to see if the offspring possess the useful qualities of both species. Diseases

It is anticipated that disease would pose a problem in siganid mariculture as it has for the culture of other fishes such as the yellowtail, Seriola quinquerudiata (Sindermann, 1970). We have already encountered several diseases in our attempts to culture S. canuliculutus in large cement tanks. The most problematic was the infestation of gills by monogenetic trematodes. Two species have been observed even on the same gills but these have not as yet been identified. They probably belong to Pseudohuliotrema or Pseudohaliotremutoides, two closely related genera, which are apparently specific to siganids (Paperna, 1972). Heavy infestations appear to cause tissue ischemia and respiratory distress, and the fish soon die, especially as the fish is sensitive to oxygen deficiency. Another gill infestation of S. canaliculutus was in the form of numerous small round white cysts (Fig. 9) which have not been identified (microsporidan Nosemu brunchiule? ). Some mortality resulted from this disease. A third disease which occurred occasionally was in the form of ulceration of the lateral line region (Fig. 10). The disease first manifested itself as a whitening of the tissue around the lateral line, followed by progressive ulceration. The fish eventually died when the ulceration was extensive. The etiology of the disease has not been studied. Other diseases encountered include exophthalmia (Fig. 1 l), unidentified white cysts or nodules in the viscera associated with emaciation, whitening of the roof of the skull, and fin rot. Obviously, proper studies of diseases and their control in siganids are badly needed.

349

Fig.9. Small white cysts on gills of S. canaliculatus.

Fig.1 0. Ulceration

of the lateral

line region

in S. canaliculafus.

Fig. 11. Exophthalmia

Production

in S. canaliculatus.

economics

An analysis of all economic as well as socio-cultural aspects of siganid farming must be carried out to determine whether the venture will be commercially viable in a given set of circumstances. No work has yet been done but costs of all aspects of production (food, nets, labour, etc.) are being carefully recorded as research proceeds. Spine irritation

and ciguatera

Siganids possess venom glands within their spines. A good description of these venom glands has been given by Halstead (1967b). A sting from any of the spines causes a sharp pain which may last from 10 to 30 min but seems otherwise harmless. Subsequent contacts seem to be less painful, suggesting that one may develop immunity towards the venom. Moreover, when the fish has been dead for some time, the spines seem no longer able to inflict any pain. Presumably,,the venom will be destroyed by cooking. A more serious problem concerns occasional reports of ciguateru poisoning as a result of eating siganids (Halstead, 1967a; Drew, 197 1; Herzberg, 1973). Ciguatera poisoning, a type of intoxication characterized

351 by certain gastrointestinal-neurological manifestations (Russell, 1969), has also been implicated in many fishes (over 440 species) including many popular food fishes (Russell, 1965; Halstead, 1967a, b). Most investigators feel that the source of ciguatoxin is marine algae and this is passed on through the food chain (see review by Russell, 1969). Algae which have been implicated are Lyngbya mujuscula (Dawson et al., 1955 ; Helfrich et al., 1968), Plectonema terebrans (Cooper, 1964; Helfrich et al., 1968) and the blue-green alga Schizothrix calcicola (Banner, 1967). Thus if questionable algae could be avoided in feeding siganids and commercial food pellets or other prepared foods used, the problem of ciguatera poisoning may not arise ip siganid mariculture. Transportation techniques

Development of air transportation techniques for siganids is not an urgent task that warrants a full-fledged research programme. However, it would be necessary if interested institutions located where siganids do not occur, or where species from other localities are to be investigated, are to participate fully in siganid mariculture research. No work has yet been done. CONCLUSIONS

There seems little doubt that siganids have great potential for mariculture. Of the holding structures investigated so far (tanks, floating cagenets and ponds), floating cage-nets offer the best prospect for a successful farming of siganids. However, there are still problems to be solved before siganid mariculture can be realized on a commercial scale. The biology of siganids, as a study, has just begun. Much more work needs to be done to provide the necessary background information for an enlightened management of siganid mariculture. ACKNOWLEDGEMENTS

_

Our work is supported by a grant from the Ministry of Science and Technology, Singapore. I am very grateful to the Lee Foundation and the Shaw Foundation for grants which enabled me to participate in The Marine Sciences Special Symposium, Hong Kong (7-14 December, 1973) where this paper was presented (an abstract of the paper will be published in the Symposium Proceedings); and to Drs. J.E. Bardach, G. Wm. Kissil, R.C. May, D. Popper, LA. Ronquillo, R.T. Tsuda and D.J. Woodland and Messrs. E.H.

3.52 Nichols and W. Chan, who have supplied me with valuable information on siganids. I am also grateful to Mr. H.K. Yip for taking and preparing the photographs, and to Mrs. J. Mui for typing the manuscript. REFERENCES Ablan,

G.L. and Rosario,

W.M. (1961)

Teuthid

fish for marine

culture

in The Philippines.

Philipp.

Bur. Fish., Fish. Gaz., 5 (4), 23-24. Ablan, G.L. and Rosario, W.M. (1962) Method of collecting and transporting live teuthid fry (padas) for stocking. Philipp. Bur. Fish. Gaz., 6, 6-8 and 36. Banner, A.H. (1967) Marine toxins from the Pacific. I. Advances in the investigation of fish toxins. In: F.E. Russell and P.R. Saunders (editors), Animal Toxins. Pergamon Press, Oxford, pp. 157-165. Ben-Tuvia, A. (1964) Two siganid fishes of the Red Sea origin in the eastern Mediterranean. Bull. Sea Fish. Rex Stn., Haifa, 37, 1-8. Ben-Tuvia, A. (1966) Red Sea fishes recently found in the Mediterranean Sea. Copeia, (2), 254-275. Ben-Tuvia, A. (1971) Culture of siganids. FAO Aquacult. Bull., 3(2), 4-5. Ben-Tuvia, A., Kiss& G.W. and Popper, D. (1973) Experiments in rearing rabbitfish (Siganus rivulatus) in sea water. Aquaculture, I, 359-364. Bini, G. (1965) Catalogue of Fishes, Molluscs and Crustaceans o,f Commercial Importance in the Mediterranean. Vito Bianco, Rome, 407 pp. Burdon, T.W. and Parry, M.L. (1954) Malayan fishing methods. J. Malay. Branch R. Asiat. Sot. Vo1.27, pt.2 (No.l66), I-180. Catanaoan, CC. (1965) For fishpond farming siganid gets acclaim. Philipp. Farms Card., October 1965, 15. Cooper, M.J. (1964) Ciguatera and other marine poisoning in the Gilbert Islands. Pac. Sci., 18, 4 11-440. Dawson, E.Y., Aleem, A.A. and Halstead, B.W. (1955) Marine algae from Palmyra Island with special reference to the feeding habits and toxicology of reef fishes. Occasional Papers Allan Hancock Found., 17. 39. De Beaufort, L.F. and Chapman, W.M. (1951) The Fishes of the Indo-Australian Archipelago. Vol. 9, Brill, Leiden. Drew, A.W. (1971) Preliminary report on klsebuul and meyas, two fish of Palau Islands. Unpublished report, dated January, 1971, 20 pp. Fowler, H.W. (1959) Fishes of Fiji. Government of Fiji, Suva, Fiji, 670 pp. Fouler, H.W. and Bean. B.A. (1929) Fishes of The Philippines and Adjacent Seas. Bull. U.S. natl. Mus. 100, ~01.8. U.S. Gov. Printing Office, Washington, D.C. 00 pp. Fujita. S. and Uena, M. (1954) On the development of the egg and prelarval stages of Siganus fuscescens (Houttuyn) by artificial insemination. Jap. J. Ichthyol., 3, 129% 132. Halstead, B.W. (1967a) Poisonous and Venomous Marine Animals of the World. Vol.2. Printing Office, Washington, D.C., p. 116.

U.S.

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