Science Philosophy Student Paper (PPs 702)

Graduate School, Institut Pertanian Bogor

Indonesia.

Instructors:

Prof Ir Rudy C Tarumingkeng, MF, PhD (Principal)

Prof Ir Zahrial Coto, MSc, PhD

BIOLOGY OF RABBITFISH IN RELATION TO

MARICULTURE PROSPECTS IN INDONESIA

BY:

SUBANDIYONO

{NRP.: P.19600002.AIR}

mailto:subandiyono@hotmail.com

PREFACE

The paper entitled ‘BIOLOGY OF RABBITFISH IN RELATION TO MARICULTURE PROSPECTS IN INDONESIA’ is one of the assignments in Philosophy of Science (PPS 702) and was made to accomplish of the subject.

The paper reviewed and discussed the biologically potential aspects of rabbitfish, one of the economically important marine fish, to mariculture, including the advantage and disadvantage characteristics of the fish. Most of the information was based on the references; however, recent experiences obtained by the author were included. Classification, description and distribution {ONTOLOGY}, the reasons why the fish was becoming more important economically and biologically to mariculture in Indonesia {EPISTEMOLOGY}, the expectations on the mariculture development of the fish in the future {TELEOLOGY}, and the contradictive situations so that mariculture activities of the fish were not well developed in Indonesia {CAUSALITY} were described. The purpose of these maricultural perspectives urgently to be developed {AXIOLOGY} was also implied.

I am grateful to Dr. Kok Leong Wee for his critical review of the paper and to Professors Rudy C. Tarumingkeng, PhD. and Zahrial Coto, PhD. for their supervisions during the class sessions.

Last but not least, any critiques to improve the paper are welcome.

The author

INTRODUCTION

Indonesia is an archipelago in which the seawater area is much bigger than the freshwater area, i.e. about 70%:30%, respectively. However, in terms of commercial fish farming, mariculture is not developed yet. One of the marine fish species that has great commercial potential for intensive culture is rabbitfish or siganids (locally named ‘beronang’ or ‘samadar’). Even though this fish has been popular as excellent seafood with a good price, there is little mass production. This is due to difficulties in larval rearing and the high larval mortalities that occurred during the first week from hatching (Ayson and Lam, 1993; Duray et al., 1994; Subandiyono et al., 1998; 1999; 2000).

Rabbitfish are widely distributed in the Indo-Pacific region, from the east coast of Africa to Polynesia, and from southern Japan to northern Australia. They can also be found in the eastern Mediterranean (Duray, 1990). They are, therefore, a fairly cosmopolitan group of fishes (Lam, 1974).

There are 26 known species of rabbitfish. This paper will only focus on those species that are important for the future of mariculture in Indonesia.

BIOLOGICAL ASPECTS

A. CLASSIFICATION

The biological classification of the rabbitfish described by Duray (1990) is as follows:

Phylum: Chordata

Subphylum: Vertebrata

Grade: Pisces

Class: Osteichthyes

Subclass: Acteropterigii

Infraclass: Neopterigii

Division: Halecostomi

Subdivision: Teleostei

Superorder: Acanthopterigii

Order: Perciformis

Family: Siganidae

Genus: Siganus (Teuthis)

Includes to this species are: S. argenteus (Quoy & Gaimard), S. canaliculatus (Park), S. corallinus, S. fuscescens (Houttunyn), S. guttatus (Bloch), S. luridis (Ruppell), S. spinus, (Linnaeus), S. vermiculatus (Cuvier & Valenciennes).

B. DESCRIPTION

In general, rabbitfish can be described morphologically as follows: 1) the body shape is compressed; 2) the body is protected by smooth and small cycloid scales; 3) the snout resembles that of a rabbit; 4) the terminal-small mouth possesses small teethes; 5) the linea lateralis is simple; and 6) the number of spines at the dorsal, anal region and ventral is 13, 7 and 2, respectively (Fig. 1). Species are identified based on their color and behavior.

Figure 1. A 32-cm body length-broodstock of S. guttatus

C. GONADAL DEVELOPMENT

The time required for one cycle gonadal development varies between species (e.g. S. canaliculatus requires about 4.5 months). Also, this is affected by several environmental conditions such as: 1) photoperiod (e.g. 18 h light : 6 h dark retards gonadal maturation of S. canaliculatus) (Lam and Soh, 1975); 2) quantity and quality of diet (e.g. females of S. guttatus fed with commercial diet containing 43% protein spawned monthly for 11 months; when lecithin, cod liver oil, or both were added to the diet, spawned occurred for at least 4 consecutive months) (Hara et al., 1986a); 3) temperature (e.g. rapid gonadal development usually occurs when the water temperature range from 25-30 ºC); and 4) lunar cycle (e.g. gonads of S. canaliculatus mature during new moon).

The development of gonads can be identified at the following stages, each characterized by the size of the ovary (Table 1).

Table 1. Development of gonads in relation to size of ovary of the rabbitfish (Alcala and Alcazar, 1979 in Duray, 1990)

*STAGE*	*SIZE OF OVARY* *(mM)*	*STAGE OF OOCYTE DEVELOPMENT*
I	14 – 70	Chromatin nucleolus and early perinucleolar oocytes
II	14 – 238	Late perinucleolar and yolk vesicle oocytes
*III*	56 – 350	Yolk vesicle and primary yolk oocytes
IV	210 – 364	Secondary and tertiary yolk oocytes
V	266 – 406	Mature oocytes
VI	336 – 420	Eggs
*VII*	14 – 70	Resting or desorbing oocytes

D. FECUNDITY AND EGG PROPERTIES

In general, absolute fecundity is higher in larger fish. Female S. canaliculatus of 11.1 – 11.5 cm body length produces 166,000 – 650,000 eggs (Lam, 1974; Woodland, 1979; Tseng and Chan, 1982), while at 21.6 – 27.3 cm body length (or about 166 – 346 g body weight) may produce 348,000 – 1,339,000 eggs (Basyari et al., 1988). A 400-g S. guttatus produces 0.8 million eggs, while a 520-g fish produces 1.2 million. Newly caught S. vermiculatus with 25 – 30 cm TL (total body length) produce 200,000 fertilized eggs (Popper and Gundermann, 1976).

When ripe, the egg is: small, spherical, demersal and strongly adhesive (Subandiyono et al., 2000; Fig. 2), except in the case of S. argenteus that are free-floating and non-adhesive (Lam, 1974). This sticky layer enables the eggs to attach to any type of substrate, whether floating or static, as spawning sites.

Figure 2. Newly fertilized eggs (±24-h embryos) of S. guttatus

The time required for egg incubation is slightly different depending on the species, water temperature, and egg diameter (Table 2). In general, bigger eggs and lower water temperature result in a relatively longer period of incubation. For example, fertilized eggs with diameter 0.42 – 0.70 mm require 18 – 35 h at 22 – 30ºC, except for S. canaliculatus that needs 62 h (Table 2).

Table 2. The relationship between egg size of rabbitfish, incubation period, water temperature and salinity

Species	*Egg* *Diameter* *(mm)*	*Incubation* *Period* *(h)*	*Water* *Temp.* *(ºC)*	*Water* *Salinity* *(ppt)*	*Type of* *Incubator* *Used*	*Refs.*
*S. argenteus*	0.62 – 0.68	-	24 – 25	40	a)	1)
*S. canaliculatus*	0.51	30	27 – 29	20.9 – 32	60-l tanks	2)
*S. guttatus*	0.55 0.55 0.54 – 0.59 0.55 – 0.57 56 - 58	20 – 26 20 18 – 20 18 – 25 24	26 – 30 26 – 29 26 – 28 27 – 30 27 – 28	Ambient 32 – 33 31 – 34 33 32	Tanks 500-l tanks Tanks b) 1-l beakers	3) 4) 5) 6) 7)
*S. luridus*	0.50 – 0.63	-	24 – 25	40	a)	1)
*S. rivulatus*	-	29 – 30	25.5 – 27	-	2-l beakers	8)
*S. vermiculatus*	0.56	24	30	-	c)	9)

a): 200-l cylindrical tanks with conical bottom and 1000-l cylindrical flat bottom tanks; b): 5-t rectangular concrete tank; c): 100-l plastic tanks and nylon mesh hatching baskets.

1) Popper et al., 1979; 2) Westernhagen and Rosenthal, 1976; 3) Juario et al., 1985; 4) Bagarinao, 1986; 5) Hara et al., 1986a; 6) Hara et al., 1986b; 7) Ayson and Lam, 1993; 8) Popper et al., 1973; 9) Popper et al., 1976

FOOD AND FEEDING HABITS

A. FIRST-FEEDING LARVAE

Rabbitfish larvae hatch with non-functional eyes and mouth; and the onset of feeding will commence after these organs become functional. Meanwhile, the larvae continue to consume the endogenous nutrient supply for their growth (Table 3).

Table 3. The transition from endogenous to exogenous feeding of rabbitfish larvae (after Kohno et al., 1988)

Phase	Period	Remarks
I	Hatching – 15 h TAH	Rapid growth due to rapid yolk resorption
II	15 – 50 h TAH	Slow growth and organogenesis based mainly on yolk energy
III	50 – 70 h TAH	Slow growth based on energy of yolk, oil globule and exogenous food
IV	70 – 90 h TAH	Slow growth based on energy from oil globule and exogenous food
V	90 – 120 h TAH	Slow growth based on energy from oil globule and certain amount of feeding
VI	120 – 150 h TAH	Accelerated growth and effective swimming and feeding based only on exogenous food
VII	Beyond 150 h TAH	Same mode as in the preceding but with accelerated increase in food consumption

Bagarinao (1986) and Subandiyono et al. (1999; 2000) found that the eyes of larvae S. guttatus become fully pigmented and the mouth opens at 36 h TAH (‘time after hatching’), while complete yolk resorption occurs at 72 h TAH. Thus, as the time required from the initial feeding to the oil globule exhaustion is relatively short (i.e. about 36 h), the provision of suitable food during this critical period is crucial for the larvae to survive further. A delay in the initial feeding beyond 24 h of eye pigmentation and mouth opening (i.e. after 60 h TAH) may be fatal for the larvae (i.e. causes 50% mortality), while starved larvae will die after 88 h TAH (Bagarinao, 1986).

Chlorella, rotifers, Brachionus sp. (in which the size less than 90 μm) can be used to improve the survival rate of the first feeding larvae (Hara et al., 1986a). Copepod nauplii may be more suitable as its size is smaller than Brachionus. However, Chlorella, Tetraselmis and Isochrysis as the sole food for the larvae will not support life beyond 4 days TAH (Duray, 1990; Subandiyono et al. 1998; 1999; 2000).

Besides phytoplankton and zooplankton, an artificial diet can be added (e.g. after 20 days TAH) when the larvae grow bigger (Bryan and Madraisau, 1977; Juario et al., 1985; Hara et al., 1986a). The use of enriched live food to feed rabbitfish larvae may improve the larval performance. Sorgeloos et al. (1988) reported that HUFA-fortified Artemia increased the growth of S. guttatus larvae.

The feeding behavior of rabbitfish larvae changes distinctly during metamorphosis (Bryan and Madraisau, 1977). At the first stage (i.e. pre-metamorphosis) they are carnivorous fish. They become omnivorous, then herbivorous at the last stage (post- metamorphosis). Furthermore, larvae of S. guttatus exhibit diurnal feeding pattern. It has been shown that the percentage of larvae with food in the gut decreases in the evening and reaches zero at 22:00 hrs. The time of active feeding (i.e. 50% of larvae with food in the gut) shifts earlier in the day with larval age.

B. JUVENILES

Whereas rabbitfish larvae are zooplankton feeders, the juveniles are primary herbivorous. Thus, the juveniles have a thick stomach wall and long intestine with a large surface area (Basyari et al., 1988). As with the larvae, the juveniles feed actively during the day to the evening and become inactive at night (Duray, 1990; Popper and Gundermann, 1975). Light may be used to attract the juveniles when collecting them from the wild. Usually, filamentous green algae are required as a lure (Ben-Tuvia et al., 1973; Bwathondi, 1982), and then a net was used to scoop the fish.

In captivity, rabbitfish required high dietary protein and energy for better growth. Parazo (1990) did an experimental feeding trial on juveniles cultured in 250-l tanks for 8 weeks. Six semi-purified diets comprising 3 levels of protein (i.e. 25, 35, and 45% of dry matter) each at 2 levels of estimated energy (i.e. 3161 and 3832 kcal/kg diet) were fed to juveniles at a stocking density of 80 fish/tank. It was concluded that the growth increased with increasing dietary protein and energy. Also, there is a positive correlation between the body weight gain and dietary protein-to-energy ratio (P/E). For diets with the same energy content but different dietary protein levels, higher P/E rations yielded better growth rate. Conversely, lower P/E rations also resulted in better growth rate for the diets containing the same protein levels but with higher energy content. Parazo (1990) suggested that the fish fed low-energy diets had insufficient total energy intake to satisfy their requirement as compared to those fed high-energy diets. However, Parazo (1990) recommended that a diet with high energy content (i.e. 3832 kcal/kg diet) and medium protein content (i.e. 35%) to be the most economical diet for juveniles S. guttatus.

Lichatowich et al. (1984) used a moistened mixture of soy meal (53%), fish meal (14%), maize (15%), flour 15%) and vitamin-mineral premix (3%) to feed 3 g-juvenile rabbitfish reared in 10-m3 cages for about 5 months. This investigations resulted in the non-significant growth rate for the juveniles stocked in different density, either monoculture or polyculture system with other fish (e.g. sea bream, Crenibus crenibus).

C. ADULT

In the wild, adult rabbitfish consume seagrass (e.g. Enhalus sp., Padina sp., Gelidium and Sargassum halophyla) or filamentous algae (e.g. Chaetomorpha sp., Enteromorpha sp. and Cladophoropsis sp.) (Basyari et al., 1988), whereas in captivity they take any types of food including the seagrass, filamentous algae, fish meals, shrimp meals, cassava flour or pelleted diet (Subandiyono, 1998; 1999; Subandiyono et al., 1996; 1997). However, adequate protein content in the diet or mixed-diet is needed as the fish (e.g. S. canaliculatus) gives poor growth rate when fed low protein diets or just seaweeds (Bwathondi, 1982).

Feeding habits of adult fish may be influenced by the food available in the area where they live, as they are opportunistic feeders. The analysis of gut content showed that the algae preferred by captive fish were not always those found in greatest quantity in the gut of wild fish (Westernhagen, 1973; 1974). Juveniles and adult S. spinus, juveniles S. argenteus, S. guttatus, S. virgatus, and S. canaliculatus prefer Enteromorpha sp. in the laboratory but take this only in small amounts in nature (Tsuda and Bryan, 1973; Westernhagen, 1973; 1974). However, Enteromorpha sp. is important in the diet of S. rivulatus and S. argenteus lived in the Elat Gulf, Middle East (Lichatowich et al., 1984). This phenomenon indicates that the differences of food preference may be related to the algal availability and other factors in the area.

D. BROODSTOCKS

The quality of diet for the broodstocks is an important factor for the survival performance of the larvae (Duray et al., 1994; Subandiyono, 1999; Subandiyono et al., 1998; 1999; 2000). Also, the age of spawner cause the fertilization and hatching rates and larval quality to decline. Juario et al. (1985) found that the percentage of larval survival rate at the first experiment varies between 6.3 – 37.4%. By using the same broodstocks, this value decreased to 0.9 – 9.0% for the next year and 0.7 – 2.0% for the next 2 years. Hormonal treatment for broodstocks prior to spawning has been investigated to improve larval performance. An experiment done by Ayson and Lam (1993) showed that larvae from females treated with 10 and 100 μg T₄-thyroxine/g fish tended to be longer and somewhat better survivors.

MARICULTURAL ASPECTS IN INDONESIA

Recently, rabbitfish are becoming more important as a mariculture product. In terms of maricultural purposes, rabbitfish possess both desirable and undesirable characteristics.

A. DESIRABLE CHARACTERISTICS:

1. The fish are an excellent food with high market value (Duray, 1990). In Indonesia they cost about twice of milkfish, a staple fish for meals. As a traditional dish during Chinese New Year, their price can be even more expensive at such time (i.e. may be twice as much as normal price).

2. Due to the beauty of their color, some of them (e.g. S. magnificus and S. vulpinus) are also sold live as an aquaria fish to America and Europe. They fetch more than US$ 100/pair (Woodland, 1979).

3. The marketable size is relatively small (i.e. varies about 100 – 300 g, depending on species). Therefore, a fast turnover for farmers, as they can grow fish to this size quickly.

4. Rabbitfish are able to take an artificial diet (Bwathondi, 1982; Juario et al., 1985; Hara et al., 1986a; Subandiyono, 1999). This encourages mass production using intensive culture system.

5. The fish can be cultured in monoculture or polyculture system with milkfish (Chanos chanos), mullets (Mugil and Liza spp.) or seabass (Lates calcarifer) (Lichatowich and Popper, 1975; Bagarinao, 1986), without affecting growth.

6. The fish spawn easily, whether naturally or by using hormonal treatment (Ayson and Lam, 1993; Subandiyono et al., 1999; 2000).

7. The fecundity is relatively high, approximately 0.8 million eggs for 400 g fish and 1.2 million for 520 g fish (depending on size and species) (Popper and Gundermann, 1976).

8. Even though the larvae are very fragile, they can be transported for 2 days using simple equipment (Basyari et al., 1988).

9. Large numbers of rabbitfish juveniles can be collected from coastal waters during certain seasons (Lam, 1974), for instance in northern coast of Java in the beginning of rainy seasons.

10. The juveniles and adults most species occupy shallow water (Lam, 1974; Popper et al., 1979). Therefore, in terms of commercial farming, they don’t require a deep cage.

11. They inhabit different types of habitat (e.g. coral reef, sandy and rocky bottom with or without vegetation, lagoons, river estuaries, and mangrove swamps) (Lam, 1974; Popper and Gundermann, 1975; Woodland and Randall, 1979).

12. Rabbitfish are able to tolerate a wide range of salinity and temperature (5 – 50 ppt and 23 – 32 ºC) with a preference range of about 10 – 35 ppt and 26 – 30ºC.

13. Rabbitfish can be used to control the growth of filamentous algae if they are stocked in shrimp ponds and tropical oyster or clam culture (Chen, 1990).

14. They can be used as a bait to catch tuna (Duray, 1990).

B. UNDESIRABLE CHARACTERISTICS:

1. In general, they grow slowly but mature early. For example, sexual maturity for male S. guttatus is about 10 months with the size about 19 cm, while the female maturity is reached after 12 months with the size about 21 cm or about 200 g. The growth rate decreases after attaining sexual maturity.

2. Even though natural or induced spawning is not a problem, especially in S. guttatus (Hara et al., 1986a; Duray et al., 1994; Subandiyono et al., 2000), mass juvenile production is still limited.

3. The time required from the initial feeding to the exhaustion of endogenous nutrient supply is relatively short, i.e. about 36 h TAH (Duray and Kohno, 1988).

4. The larvae have a relatively small mouth gape at the first opening, i.e. about 125 μm (Duray and Kohno, 1988). Therefore, they need small size feeds.

5. The fish are difficult to handle due to the poisonous spines that may induce severe headaches (Herzberg, 1973).

6. The sex is difficult to distinguish except during the breeding season (Duray, 1990).

7. It is difficult to differentiate between the species due to only a few morphological differences. Therefore, the identification relies only on the coloration of live fish, habitat, and behavioral characteristics (Woodland and Randall, 1979).

CONCLUSIONS

As the biologically aspects and feeding habits of rabbitfish vary between species, special attention to one or few species that have commercial potential for mariculture is needed. Considerations include the ease of spawning, with or without hormonal treatment. The chosen species should be fecund, fast growing, hardy and suited to intensive culture. The important species for mariculture in Indonesia are S. vermiculatus, S. guttatus, S. canaliculatus and S. javus.

These fish have potential prospects to be cultured commercially in Indonesia as they are suited to the local growing conditions and are a recognized delicacy with a high market value. Other factors which encourage the farming of rabbitfish in Indonesia are: 1) the fish can be grown using a simple floating cage (e.g. made of bamboo which is abundant in Indonesia; 2) sites suited to this type of fish farm are easy to find; 3) many types of commercial diet for fish have been produced in a large quantity; and 4) labor cost is relatively cheaper. Therefore, rabbitfish farming has tremendous potential in Indonesia.

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