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New Direction in Fish Feeds and Feeding: Long Term Implications Chhorn Lim Nutrition Scientist Aquatic Animal Health Research Unit USDA-ARS, MSA P.O. Box 952 Auburn, Alabama 36831 Extended Summary Aquaculture production of fish and shrimp has expanded rapidly in the past decade and is predicted to continue to grow steadily for the foreseeable future as the world population increases and demand for quality seafood continues to rise. Paralleling the growth of the industry has been the intensification of aquaculture production leading to an increased use of compound feeds. Successful operation of these production systems is dependent, among other factors, on the availability of good nutrition (feed and feeding). Since feed cost represents the major proportion of the overall production cost in intensive aquaculture, the availability of low-cost, nutritionally balanced diets are critical. Fish meal, because of its high protein content, amino acid profile closely matches the fish dietary requirements, high protein and amino acid digestibility, and high palatability, has been used as the major protein source for most aquaculture species . However, due to the increased demand, uncertain availability and rising cost of fish meal, considerable attention has been devoted to progressively substitute fish meal with alternative protein sources which are less expensive and more readily available. Byproducts of the animal rendering industry such as meat meal, meat and bone meal, blood meal, are high in protein and relatively well digested by most fish. Protein quality and palatability of these products are somewhat inferior to fish meal. Research has demonstrated that these products and their combination can be used to partially or totally replace fish meal, depending on fish species. Meat and bone meal is a good source of minerals. Its high ash content, however, may limit its use in fish feeds due to possible mineral imbalances. It has been recommended that meat meal, meat and bone meal and blood meal or their mixture may be used at a level of 5 to 10% in fish feeds, provided that feeds contain adequate levels of essential amino acids. Because of bovine spongiform encephalopathy or “mad cow disease”, these products are banned in animal or fish feeds in EU countries and are generally avoided in aquaculture feeds in countries that export aquaculture products to EU countries. Some fish feed manufacturers in the U.S. have voluntarily discontinued the use of meat and bone meal as a precautionary measure. Poultry byproduct meal has also been used successfully as partial or total replacement of fish meal, depending on the species. On an equal protein basis, poultry byproduct meal can substitute 35 to 70% of fish meal in diets of most aquaculture species. The nutritional value of feather meal is poorer than that of poultry byproduct meal. Many plant protein ingredients have been used in domestic animal feeds but relatively few are used in fish feeds because fish have high dietary protein requirements (25 to 45%). Consequently, only high protein content plant feedstuffs are used in fish feeds. Oil seed byproducts such as soybean meal, rapeseed meal and cottonseed meal, because of their availability and low cost, are the most promising alternative protein sources for fish feeds. Compared to fish meal, these plant ingredients are commonly deficient in lysine and methionine, and contain indigestible carbohydrates, phytin, tannin, allergens and antinutritional factors/toxins such as trypsin inhibitors in soybean meal, glucosinolates in rapeseed meal and gossypol in cottonseed meal. Various soybean products have been used successfully as substitutes for 25 to 80% fish meal in fish diets, depending on the species and type of product. Salmonids and carnivorous fish tolerate lower dietary levels of soybean products than omnivorous or herbivorous fish. Higher levels of fish meal can be substituted if soy protein concentrate is used. Acceptable inclusion levels of rapeseed/canola (low erucic acid and glucosinolates rapeseed) meal range from 10 to 25% depending on the species and age of the fish, and the glucosinolate content of the meal. The amount of cottonseed meal that can be included in fish diets depend primarily on the levels of free gossypol and available lysine. Because free gossypol is bound to lysine during processing of cottonseed into meal, lysine availability decreases as free gossypol decreases. Available data indicate that, depending on the species, solvent extracted cottonseed meal can be incorporated in fish diets at levels of 10 to 30%. Numerous studies have shown, however, that high levels of these plant ingredients usually resulted in poor performance due mainly to reduced feed consumption, deficiency of essential amino acids and energy, and presence of anti-nutritional factors, toxins and indigestible components such phytin and non-starch polysaccharides. Supplementation of deficient amino acids with crystalline amino acids has shown to improve the nutritional values of these plant feed stuffs. Dietary addition of exogenous enzyme, phytase, has been shown to increase the phytin phosphorus availability to numerous fish species. Feed consumption can also be improved by dietary addition of palatability enhancers such as fish hydrolysates, fish oil and certain amino acids such as glycine. It is expected that the percentages of fish meal used in future fish feeds will decrease and higher percentages of alternative protein sources will be used. This created several problems such as balancing the essential amino acid content in the diets, increasing the nutrient retention/availability, eliminating counteracting the physiological effects of antinutritional factors and improving the diet palatability. This is particularly important when high levels of plant ptotein ingredients are used. However, in certain regions of the world where alternative protein sources are expensive relative to the price of fish meal, aquaculture diets still contain substantial amount of fish meal. The benefit of using good quality feed can only be realized if fish are properly fed. For maximum growth, farmers are interested in high rates of feed consumption. However, uneaten or excess feed cannot be recovered and represent not only an economic loss, but also deteriorate water quality. Thus, for fish farming to be profitable and sustainable, good feeding practices (feed allowance, feeding method, feeding frequency and daily feeding schedule) must be applied. However, because numerous factors such as culture system and intensity, fish species and size, water quality variables, feed palatability and quality influence fish feeding, feeding strategies for several fish species have not been worked out.