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  1. Identity
    1. Biological features
    2. Images gallery
  2. Profile
    1. Historical background
    2. Main producer countries
    3. Habitat and biology
  3. Production
    1. Production cycle
    2. Production systems
    3. Diseases and control measures
  4. Statistics
    1. Production statistics
    2. Market and trade
  1. Status and trends
    1. Main issues
      1. References
        1. Related links
      Identity


      Siganus spp. [Siganidae]
      FAO Names:  En - Spinefeet(=Rabbitfishes) nei,   Fr - Sigans nca,  Es - Síganos nep
         
      Biological features
      Rabbitfishes are composed of 28 species belonging to the genus Siganus. Rabbitfishes are distributed across the Indo-Pacific Ocean ranging from the Red Sea and the Gulf to French Polynesia and from Japan to southern Australia. Based on morphology and ecology, rabbitfishes have been split into two groups: those that are drab coloured, fusiform and school in macro-algal habitats (e.g. S. argenteus, S. canaliculatus, S. spinus) and those that are brightly-coloured, reef associated and pairing (S. doliatus, S. corallinus, S. vulpinus). Molecular analysis has identified a third group consisting of the fusiform schooling S. argenteus and the deep-bodied S. woodlandi. In general, rabbitfish are morphologically similar having a deep and compressed body with a rounded blunt snout, with the exception a few species which have a distinctive tubulate snout and distinctive facial markings reminiscent of a fox, previously classified in the genus Lo. There are a number of spines along the fins: 13 in the dorsal fin, 7 spines in the anal fin, and 2 spines in the ventral fin. Colour ranges from olive-green to brown. Scales are smooth and small.
      Images gallery
      Experimental floating cages in the Solomon Islands. Source: Teitelbaum et al. 2008.Sea cages for Siganus canaliculatus in India. Source: Jaikumar et al. 2011
      Concrete tank culture for S. canaliculatus. Source: Jaikumar et al. 2011.Marine cages with Siganus rivulatus in Cyprus. Courtesy of George Anastasiades, 2007.
      Profile
      Historical background
      Rabbitfishes are nutritionally important fish with economic value in several Indo-Pacific countries/regions including Palau, Guam, Fiji, New Caledonia, New Hebrides and the Solomon Islands, the Philippines, Singapore, Malaysia, Japan, China and Sri Lanka, as well as Eastern Mediterranean nations. Several of these nations have dabbled with aquaculture but large-scale rabbitfish farming did not catch on probably because the fish is inexpensive yet has similar culture requirements to expensive carnivorous fish. As concerns about the sustainability of fishmeal use in aquaculture increase, interest in the farming of algivorous species such as rabbitfishes will grow. Rabbitfishes have been cultured in the Philippines, India, Saudi Arabia and Cyprus. There are also reports of extensive production of rabbitfishes in Tanzania, Australia and Indonesia.
      Active interest in the potential of rabbitfish aquaculture started around the 1970s. In 1972 a Siganid Mariculture Group was formed during a meeting at the Hawaii Institute of Marine Biology to plan a Siganid Fish Farming Program (1974). However, some small-scale rearing of rabbitfish species occurred in the Philippines prior to the 1970s.
      Main producer countries
      Main producer countries of Siganus spp. (FAO Fishery Statistics, 2018)
      The map shows main producing countries of rabbitfish based on FAO reported statistics. However, the authors based on their knowledge, affirm that the main rabbitfish producing countries since 2000 have been Indonesia and the Philippines. Some siganids are produced in Egypt, India, and Saudi Arabia. Bahrain, Fiji, Mauritius, Qatar, Singapore, and United Arab Emirates have also cultured siganids intermittently but discontinued this activity for undisclosed reasons.
      Habitat and biology
      Most rabbitfishes occupy shallow areas around corals, mangrove swamps, kelp beds and harbours. Species such as S. guttatus and S. vermiculatus have also been noted to enter rivers and lakes. Some rabbitfishes, such as S. canaliculatus and S. rivulatus, have been found to tolerate wide ranges of temperatures (eurythermal) and salinities (euryhaline).

      Rabbitfishes generally swim and feed in schools although some live in pairs. The schooling behaviour of some of the rabbitfishes is attractive to aquaculturists because it permits high stocking densities.

      In general, larval rabbitfish are plankton feeders and the juvenile and adult rabbitfish are primarily herbivorous. The morphology of the mouth and gut reflects the herbivorous nature of the fish: small mouth, many conical teeth in jaws in addition to pharyngeal teeth, thin-walled stomach, long, coiled and thin-walled intestine. Some of the items found in the natural diet of the rabbitfishes include filamentous green algae, seagrasses, brown algae and diatoms. However rabbitfishes are not obligatory herbivores. Some rabbitfishes have been noted to consume detritus, sediment and sponges in the wild. In captivity, S. canaliculatus and S. rivulatus consume both plant and animal sourced ingredients.

      No clear differences have been noted between male and female rabbitfishes except prior to spawning. In general, males are smaller than females; maturing standard lengths are 11-14 cm for males and 13-21 cm for females. The maximum attainable sizes range from 20-45 cm standard length. In general, rabbitfishes spawn in late spring/early summer but in some species autumn or year-round spawning has been noted. Spawning follows a lunar periodicity, often occurring in the week following the new moon. Juveniles tend to grow rapidly, reaching adult size in about 6-8 months. In captivity, rabbitfishes held in optimum environmental conditions mature earlier than in the wild.
      Production
      Production cycle

      Production cycle of rabbitfishes (Siganus spp.)

      Production systems
      The rabbitfishes of interest to aquaculture include: Siganus canaliculatus, S. guttatus, S. virgatus, S. spinus, S. punctatus, S. fuscescens and S. javus in Malaysia, the Philippines and Indonesia; S. canaliculatus on the east coast of Africa; S. rivulatus in the Middle East and Mediterranean region; and S. randalli, S. lineatus and S. fuscescens in the Pacific region. Three rabbitfishes (S. canaliculatus, S. fuscescens and S. guttatus) have also been cultured in China.

      In the Philippines, rabbitfish are either monocultured or polycultured with milkfish in ponds. The ponds usually rely on brackishwater pumped from a river. Floating cages have also been used for the rearing of rabbitfish. These are made from bamboo or nylon nets, depending on the country. Floating cages are often placed in protected areas with at least 3 m water depth at the lowest tide. In China, rabbitfishes have been cultured both in monoculture and in polyculture with sugpo (Penaeus monodon), mud crab (Scylla paramamosain), milkfish (Chanos chanos), black bream (Sparus latus), Japanese croaker (Nibea japonica), large yellow croaker and groupers (Epinephalus spp.) both in ponds and in sea cages. There are no references to siganid farming in recirculation systems.
      Seed supply 
      Juvenile fry (1 to 7 cm) are often collected from local reef areas approximately one month after spawning events. The juveniles may be collected using push nets, scoop or seine nets, throw nets, lift nets, and fyke nets. Artificial light or various lures (e.g. stale bread, algae) are used to bait traps. The fry are often transported using hauling tanks with well-oxygenated seawater. Low doses of anesthetic (e.g. MS-222, clove oil) are also used in some cases to reduce handling stress.
      Hatchery production 
      The natural spawning of rabbitfishes follows the lunar cycle. Female rabbitfishes have been successfully induced to spawn by hormonal treatments (e.g. human chorionic gonadotropin, luteinizing hormone-releasing hormone analogue), dietary (e.g. clomiphene citrate) and physical manipulations (e.g. handling stress, drop in natural water levels). Less work has been done on the induction of male spermiation. However, some studies indicate the induction of spermiation using hormonal treatments. There is limited knowledge on the broodstock nutrition of rabbitfishes. For S. guttatus a diet containing 42 percent protein was found suitable for monthly spawning but fertilization, hatching rates and larval quality decreased with the age of the spawner. In general, it is recommended to feed broodstock with a diet high in energy and protein but low in ash. Hatcheries in Indonesia, the Philippines and Cyprus often just stock females and males together in large spawning tanks, add spawning matts and manipulate temperature and light regimes to emulate spring conditions. The fish appear to spawn naturally one week after the full moon and the matts are then collected and incubated separately.

      Rabbitfish eggs are small (0.42-0.70 mm in diameter), demersal, adhesive and take about 18-35 h to hatch at 22-30 °C. The larvae are pelagic and range between 1.5-2.5 mm in total length. Survival of larvae in captivity for four species (S. lineatus, S. vermiculatus, S. fuscescens, and S. guttatus) have been observed to range from 0.2 to 38.0 percent.

      There is limited knowledge on optimum water quality parameters during the embryonic and larval development of rabbitfishes. Apparently, in species such as S. guttatus, naturally spawned eggs are more tolerant to salinity variations than hatchery spawned eggs. Salinity ranges of 15.8 to 32.2 ppt for eggs and larvae have been noted for S. canaliculatus. Reduced temperatures (22-26 °C) have been observed to improve survival rates in S. guttatus. In the hatchery, larvae are fed rotifers, Artemia nauplii and artificial diets at about 27-28 percent of their body mass. For S. guttatus a diet of 40 percent protein with an energy content of 3971 kcal kg-1 has been recommended. However, few studies on the nutritional requirements of larval rabbitfishes have been conducted.
      Nursery 
      There are no published reports of nurseries for rabbitfish fingerlings. However, based on studies performed on other fishes, the authors assume that nurseries would be very beneficial to aquaculture production.
      Ongrowing techniques 
      The time taken for the larvae to metamorphose and develop into juveniles depends on the species; it is 45 days in S. guttatus (22.0 mm, total length), 21 days in S. canaliculatus (20-24 mm, total length), and 11 days in S. fuscescens (9.5 mm, total length). Research suggests that rabbitfish fingerlings can be farmed in ponds, cages or tanks. Juveniles of several rabbitfish species are tolerant to wide ranges of salinity and temperature. S. canaliculatus can tolerate salinities as low as 5 ppt and the optimum salinity for growth and survival has been reported to be 10 ppt. S. rivulatus has been found to tolerate salinities between 10 and 50 ppt with an optimum salinity of 35 ppt. S. rivulatus has also been found to tolerate temperature ranges from 17 to 32 °C with an optimum of 27 °C. Some rabbitfishes appear to be tolerant of hypoxia down to about 1 mg/L.

      The growth rate of rabbitfishes depends on the rearing system and techniques. Growth of cage-held S. guttatus has been reported to be initially slow, increasing to a faster pre-adult growth whereas in S. rivulatus initial growth is rapid until 2 years of age and decreases afterwards. In ponds stocked with S. randalli juveniles (3 cm) at a density of 15 fish/m2, the fish are harvested after a 6 month period at around 100 g and the overall survival rate is about 80 percent. Some research suggests that for schooling varieties of rabbitfishes, stocking densities of 50 fish/m2 or more are possible. In experimental recirculating systems, no effects on survival and growth of S. rivulatus stocked at densities ranging from 10 and 40 fish per 50 litres aquarium were reported.

      A number of nutritional studies have been performed to determine the optimal dietary requirements of juvenile rabbitfishes in captivity. For example, for S. javus, a diet containing 35-46 percent protein improved growth significantly as compared to diets containing 29 or 58 percent protein. For S. canaliculatus, a diet containing 25 percent crude protein and 5 percent sunflower oil resulted in optimal growth of fry during a 70 day trial. For S. rivulatus reared in recirculating systems, diets containing 40 percent crude protein (CP) and 14.2 millijoules/kg digestible energy/kg resulted in best growth.

      Rabbitfishes are generally harvested by net and placed on ice to be transported to processing centers or directly to market. The only handling and processing issue is the presence of a toxic spine on their dorsal fin that can be quite painful for handlers. The toxin is not dangerous to processors or consumers.
      Diseases and control measures
      The following table shows some of the common pathogens noted in cultured rabbitfishes.

      DISEASEAGENTTYPESYNDROMEMEASURES
      MycobacteriosisMycobacterium marinumBacteriaUncoordinated swimming; abdominal swelling; loss of weight; skin ulceration; white nodule formation as granuloma in liver, kidney and spleen in both freshwater and marine fishProphylaxis and vaccine development
      PseudomonasShewanella (Pseudomonas) putrefaciensBacteriaDiscoloration; haemorrhagic necrosis on body and mouth; frayed fins; exophthalmia; lethargic fishVaccination
      Streptococcal infectionEnterococcus faecalis, Enterococcus faecium, Streptococcus iniaeBacteriaChange in body coloration; sluggish movement; blindnessAntibiotic treatment
      Caligid copepodsPseudocaligus uniartus and Lepeophtheirus siganiParasiteSevere erosion and haemorrhaging of body surface, fins and eyesFlow-through freshwater for four hours may prevent further infection and mortality
      Statistics
      Production statistics
       
      Market and trade
      The processing of rabbitfishes generally involves sorting by size, gutting and washing. Siganids are not reported to have export markets and are usually consumed fresh in the region of production. There are no reports of siganids being sold as filets or frozen for long-term storage or shipping. Rabbitfish are marketed fresh in markets and restaurants (e.g. Mediterranean Sea, Asia). Additionally, in Asian markets, some are split and sun-dried before being sold. In some East African coastal areas, siganids of all sizes are smoked and sold in local markets mixed with other coastal fish species.

      Rabbitfishes are not expensive in most Indo-Pacific nations or in the Gulf and Red Sea countries. In the United Arab Emirates prices are around USD 3.7/kg. However, in some remote South Pacific islands such as New Caledonia, S. lineatus is sold for USD14-18/kg. Prices of Siganus rivulatus and S. luridus in the Lebanese market are around USD7/kg but can reach USD50/kg in restaurants in Cyprus.
      Status and trends
      Research
      Culture protocols for rabbitfishes (e.g. S. rivulatus, S. canaliculatus) are being developed. Research is being performed on basic environmental requirements, physiology, culture protocols, nutritional requirements, diseases, stress and immune response. Actual aquaculture is not yet based on empirical scientific findings but rather on a mix of science, experience with other species and trial and error. Interestingly, rabbitfish culture has progressed from monoculture to polyculture in China which appears to be more economically sustainable and environmentally friendly than monoculture. Polyculture of S. lineatus with shrimp appears to decrease the impact of diseases, prevent environmental deterioration and increase pond and water productivity.

      Perspectives
      Farming lower tropic-level species addresses some of the environmental concerns of aquaculture. Some challenges to the expansion of rabbitfish aquaculture include the provision of hatchery produced fingerlings to replace wild sourced fish, the development of specialized diets for the fish (based on algae if possible) and a better understanding of diseases and their mitigation.
      Presently, rabbitfishes have niche markets, mainly in regions where a fishery already exists. Moreover, rabbitfishes differ by region and a species known by one population might not be acceptable to another. If rabbitfishes are to become “the tilapia of the ocean” then one or two species need to be chosen for aquaculture and marketing considerations and research focused on these. Rabbitfish have the potential of becoming an inexpensive and healthy marine fish with worldwide demand. Some species, such as S. javus, can reach weights in excess of 3 kg, have good markets and grow quite rapidly.

      Recommendations
      Further research is needed into the basic requirements of various species. Developing the rabbitfish aquaculture sector would be advantageous for diversification especially since it is one of the few marine herbivorous cultured species.

      Main issues
      If rabbitfish are to become globally recognized like tilapia, they will probably have to be genetically selected for good production characteristics and possibly farmed outside their native range. This raises concerns such as exotic introductions and the possibility of escapes and disease transmission, as well as the environmental degradation related to practically all aspects of animal husbandry. An issue specific to rabbitfish is that escapees may exert increased pressure on local algal/seagrass biomass because they are voracious herbivores.

      References
      Bibliography 
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      Babikian, J., Nasser, N., Saoud, I.P. 2017. Effects of salinity on standard metabolic rate of juvenile marbled spinefoot (Siganus rivulatus). Aquaculture Research, 48: 2561-2566.
      Ben-Tuvia, A. 1985. The impact of the Lessepsian (Suez Canal) fish migration on the eastern Mediterranean ecosystem. In: Mediterranean marine ecosystems. M. Moraitou-Postolopoulou and V. Kiortsis (Eds). Plenum Press, New York, pp. 367–375.
      Cruz-Lacierda, E.R., Pagador, G.E., Yamamoto, A. and Nagasawa, K. 2011. Parasitic caligid copepods of farmed marine fishes in the Philippines. In: Diseases in Asian Aquaculture VII. Selangor, Malaysia: Fish Health Section, Asian Fisheries Society, pp. 53-62.
      Diamant, A., Banet, A., Ucko, M., Colorni, A., Knibb, W. and Kvitt, H. 2000. Mycobacteriosis in wild rabbitfish Siganus rivulatus associated with cage farming in the Gulf of Eilat, Red Sea. Diseases of Aquatic Organisms, 39: 211-219.
      Duray, M.N. 1990. Biology and Culture of Siganids. Aquaculture Department, Southeast Asian Fisheries Development Center (SEAFDEC), Iloilo, Philippines, pp. 1-47.
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      Jaikumar, M., Kanagu, L., Stella, C., Gunalan, B. (2011. Culturing a rabbit fish (Siganus canaliculatus) in cages: A study from Palk Bay, South East Coast of India. International Journal of Water Resources and Environmental Engineering, 3: 251-257.
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