Introduction Groupers are territorial predatory reef fish that are widely distributed throughout the tropical and subtropical seas of the world, and notably, those of the Indo-Pacific region. A very diverse group of fish comprising more than 90 species in five main genera of the family Serranidae, they are highly prized in the live reef fish markets of Hong Kong and Singapore where they fetch from US$10-12/kg for orange-spot grouper Epinephelus coioides, US$40-50/kg for coral trout Plectropomus spp to more than US$80/kg for humpback grouper Cromileptes altivelis (Sim, 2005). Targeting of spawning aggregations and destructive fishing practices such as the use of cyanide and explosives have resulted in these fish being severely depleted in the wild. A major impediment to aquaculture production of groupers has been the limited supply of fry. While a significant industry has been established in South East Asia based on wild- capture fry, only the lower value estuarine species such as orange-spot grouper and marbled grouper Epinephelus malabaricus are caught in any significant numbers. Fry of the higher value, coral reef-dwelling species such as coral trout and humpback grouper are seldom caught other than as incidental catches by those targeting the aquarium trade. Until recently, commercial hatchery-production of grouper fry has been very Market-size coral trout, Plectropomus leopardus, difficult with survival rates to metamorphosis typically less Photo credit: SY Sim, NACA than 5%. Advances in grouper hatchery technology (Rimmer et al., 2004; Sim et al., 2005a) are now overcoming this Trash fish still the preferred feed for groupers bottleneck. Fry of many grouper species, including orange- spot, tiger (Epinephelus fuscoguttatus) and humpback grouper, Throughout the Asia-Pacific region, the traditional are becoming more readily available for aquaculture grow-out. and still preferred method of culturing groupers, is to feed them on low-value fresh fish ('trash fish'). Trash fish that is fresh, properly prepared and carefully managed can be a very good, and often inexpensive, source of food for carnivorous marine fish such as groupers. Sadly, this is often not the case and even in well managed systems, the feeding of trash fish can have negative financial, environmental and social impacts 'triple bottom line' consequences. There are three main concerns: depletion of fish stocks and the resultant increased competition between man and aquaculture for a dwindling (and more expensive) supply of wild fish, adverse environmental impacts associated with the feeding of trash fish and spread of diseases to wild and cultured fish. The demand for low-value fish in the region has steadily increased with continued expansion of mariculture. Satisfying this demand has caused a severe problem of over- fishing, not only of the traditionally-fished stocks, but also of Market-size orange spotted grouper, Epinephelus coioides those fish and invertebrates closer to the bottom of marine food Photo credit: SY Sim, NACA chains. Many coastal fish stocks in SE Asia are reported to be 20 Aqua Feeds: Formulation & Beyond, Volume 2 Issue 2 2005 10 to 30% below the levels of three decades ago (Williams, 2002). The feeding of trash fish itself is a significant source of pollution. Feed losses associated with feeding trash fish to carnivorous fish are four times greater than feeding pelleted feeds. However, this may be an underestimate. New (1996) cites a 1991 study in Hong Kong where 45,000 t of trash fish were needed to produce just 3,000 t of high-value food fish in marine cages i.e., a FCR of 15:1. Where trash fish is carefully fed, as for example under experimental conditions, FCRs for cage-cultured groupers can be as good as 3.5:1 on a wet basis. However, under practical farming conditions, FCRs are more typically 6:1 and up to 17:1 (Tacon et al., 1991). An often ignored consequence of feeding trash fish is the likelihood of it being a direct or indirect source of introduced disease. Of particular concern are viral diseases such as viral nervous necrosis (VNN), bacterial infections, particularly by Vibrio and Streptococci, and parasites. While the main mode of VNN transmission is vertical from the egg, horizontal transmission from other infected fish, including trash fish, is also a real threat. Too often, the nutritional inadequacy of the trash fish, Fingerlings of humpback grouper, Cromileptes altivelis especially where spoilage occurs prior to it being fed, is a real, Photo credit: SY Sim, NACA but generally unrecognized problem that results in slow growth, poor FCRs and lower survival. flow to ensure fish have well oxygenated water. Fingerlings of 25-75 mm (14 g/fish) are stocked at 100-150 fish/m2 and cannibalism reduced by grading the fish every one to two weeks until they are 125-150 mm (30-80 g/fish). At this size, the fish are transferred from nursery cages into production cages where stocking density is typically 50-60 fish/m2 initially, reducing to about 10-20 fish/m2 for fish of 500+ g. Another, but less common, culture system is to use brackish water ponds, often reclaimed shrimp ponds of any size up to about 0.5 ha. This culture system is suitable for estuary species such as orange-spot or marbled groupers but has not proved very successful for true marine groupers such as tiger or humpback. For brackish water pond culture, newly introduced fingerlings are restricted to a small netted enclosure of the pond for several weeks while being trained to the feeding method. The fish are then let out of the enclosure to free-range in the pond. Groupers are fed to apparent satiation during the day with feeding frequency decreasing as the size of the fish increases. Farmers check cages and ponds daily to remove uneaten food and to adjust feeding rate so as to minimize food wastage. Broodstock of humpback grouper, Cromileptes altivelis Guidelines for the amount and frequency of feeding trash fish Photo credit: SY Sim, NACA or compounded (pelleted or extruded) dry feeds are given in Table 1. The preferred harvest size of farmed groupers is 600 g Farming practices to 1.2 kg, depending on the market. Under farm conditions, orange-spot and tiger grouper will reach weights of 600 g in Groupers are most commonly farmed using knotless nylon or about 6-8 months and 1-1.2 kg in about 12 months after being polyethylene net sea cages, typically as a raft of floating cages, stocked as 100 mm fingerlings. Survival rates after 100 mm each of 2 to 5 m sides and 2-3 m deep. Where possible, cages are size are typically 85% or better. situated in channels where there is deep water and good tidal Table 1: Guidelines1 for feeding trash fish or compounded (pelleted) dry feeds to Epinephelus species of groupers Daily feeding rate (% of average body weight) Fish size (g) Number of feeds/day Trash fish Dry feed 1-5 20 20 10 4 3-5 5-25 20 15 4 2 2-3 25-100 15 10 2 1.5 2 100-200 10 8 1.5 1.2 1-2 > 200 6 4 1 0.8 1 1 The amount of food to be given and the frequency of feeding must be carefully monitored and adjusted for each farm situation,. The feeding schedule in the table should only be used as a guide. For slow growing species such as humpback grouper (C. altivelis), the amount to feed should be reduced by about a half. Aqua Feeds: Formulation & Beyond, Volume 2 Issue 2 2005 21 Preparation of trash fish for feeding to groupers Farm-made pellet feeds for groupers Photo credit: SY Sim, NACA Photo credit: SY Sim, NACA Table 2: The dry matter, crude protein and energy apparent digestibility coefficients (mean ± SD) determined with groupers for selected ingredients available in SE Asia Digestibility (%)1 Feed ingredient Dry Matter Crude Protein Energy Marine product Acetes shrimp meal (72% CP) 76.0 ±4.00 95.0 ±0.72 Fish meal (Chilean, 65% CP) 83.6 ±3.09 98.0 ±0.07 Fish meal (local, 45% CP) 59.1 ±1.23 82.4 ±1.99 77.2 ± 1.91 Fish meal (sardine, 65% CP) 87.2 ±2.53 85.2 ± 0.90 92.5 ±1.40 Fish meal (tuna, 50% CP) 75.4 ±3.61 76.2 ±1.92 Fish meal (white, 69% CP) 89.2 ±1.69 98.6 ±0.31 Shrimp head meal (50% CP) 58.5 ±3.33 78.0 ±1.32 63.6 ±0.89 Squid meal (71% CP) 99.4 ±0.95 94.2 ±0.21 Terrestrial animal product Blood meal (ring-dried, 84% CP) 36.9 ± 0.98 15.5 ± 2.01 Blood meal (oven-dried, 84% CP) 48.1 ± 0.85 55.2 ± 1.35 Blood meal (formic, 87% CP)2 67.9 ± 1.63 87.5 ± 0.55 Blood meal (propionic, 84% CP)2 61.7 ± 2.60 84.2 ± 0.69 Meat meal (Australian, 44% CP) 60.8 ± 0.80 98.9 ± 1.32 Meat meal (Philippine, 45% CP) 77.7 ± 0.09 83.8 ± 1.66 Meat solubles (Danish, 73% CP) 99.3 ± 0.45 97.6 ± 0.08 Poultry feather meal (67% CP) 74.3 ± 3.06 81.8 ± 2.58 Terrestrial plant product Corn meal (8% CP) 85.2 ± 2.81 82.9 ± 4.71 Corn gluten meal (56% CP) 94.0 ± 2.03 99.5 ± 0.65 Cowpea meal (white, 24% CP) 74.2 ± 3.14 93.5 ± 1.22 Lucaena (ipil-ipil) meal (19% CP) 56.0 ± 0.04 78.8 ± 2.64 Lupin albus meal (26% CP) 54.1 ± 1.24 97.5 ± 3.65 Palm oil cake meal (11% CP) 45.3 ± 2.37 80.5 ± 1.30 40.4 ± 3.74 Rice bran (11% CP) 22.2 ± 1.52 59.5 ± 1.41 44.3 ± 0.97 Rice bran (14% CP) 68.5 ± 7.02 42.7 ± 5.38 Soybean meal (full-fat, 41% CP) 54.8 ± 2.72 67.2 ± 1.29 51.1 ± 0.89 Soybean meal (solvent-extracted, 75.7 ± 1.98 96.0 ± 0.13 50-54% CP) Wheat flour (9% CP) 72.8 ± 0.85 82.9 ± 1.26 1Mean ± SD.