WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2023 43 reduced by the activity of phytase releasing phosphorus bound in phytate. Addition of phytase also decreases the phosphorus load into the environment by making it more available to the fish for growth. Phytasesupplemented diets have been shown to improve metabolic activities like feed intake, growth and food conversion efficiency. Non-starch Polysaccharide (NSP) Utilization in Aquafeed Non-starch polysaccharides (NSPs) present in plant materials are important anti-nutritional factors that have been found to reduce the performance of various animals. They make nutrients less available for digestion due to the increased viscosity of the material in the intestine. The lack of intestinal enzymes for the degradation of non-starch polysaccharides can be overcome by supplementation of degrading enzymes. This approach allows more flexibility in feed formulation and reduces feed costs while improving feed efficiency and availability of metabolizable energy. Factors Contributing to the Use of Enzymes in Aquafeeds • High demand for quality grain-based food for fish/shrimp. • High demand for quality animal products and by-products. • The need for alternate sources of feed ingredients with better nutritive value. • Economic incentives (cost : benefit). • Sustainability considerations. • Environmental awareness. Aquafeed Enzymes and Sustainable Aquaculture Feed is the major input of intensive aquaculture, typically involving 50 to 60 per cent of total operational costs. The success of sustainable aquaculture depends on economically viable and eco-friendly aquafeeds. Use of the most preferred feed ingredient, fishmeal, is declining because of increasing prices due to competition with other livestock industries for available supplies. Hence, researchers are focusing on fishmeal alternatives. One such alternative is to substitute fishmeal with plant-based proteins in conjunction with feed enzymes. Phytase releases the phosphorus bound to phytate in plant ingredients and this allows feed manufacturers to reduce levels of fishmeal and, consequently, the cost of feed production. More efficient phosphorus utilization can in turn help reduce the problem of eutrophication. There is no harm in using enzymes in aquafeeds because they are natural products of fermentation and cannot pose any threat to fish or shrimp health, nor to the pond environment. The reduction in the release of phosphorus and ammonia are positive factors of tract of aquatic animals are potent producers of digestive enzymes, and addition of live microorganisms to diets for enzyme production is also possible in specialty feed applications. Largescale commercial enzyme supplementation relies on enzymes produced by microbial fermentation technology. Enzyme Types Many enzymes have been used in fish/shrimp nutrition over the past several years including cellulase, β-glucanases, xylanases and associated enzymes like phytase, proteases, lipases and galactosidases. Enzymes are used for neutralizing the effects of viscous non-starch polysaccharides (NSPs) in cereals and other food grains in animal feed industries. Uses of Feed Enzymes Aquafeed enzymes incorporated in the diets of fishes and shellfish can promote a variety of benefits to these animals including: • Enhanced digestion and absorption of nutrients, especially fat and protein. • Improved Apparent Metabolizable Energy (AME) dietary values. • Reduced digestive viscosity. • Increased feed intake, weight gain and feed gain ratio. • Reduced ammonia production. Enzymes and Function The basic function of endogenous enzymes for cultured fish or shrimp is to help in the breakdown of large complex organic molecules like starches, proteins and cellulose. Supplementation of exogenous carbohydratases increases the utilization of otherwise unavailable dietary carbohydrates. High levels of non-starch polysaccharides (NSPs) such as cellulose, mannans and xylans reduce the nutritive value of many plant-based ingredients. Intestinal enzymes for digestion of these carbohydrate sources are not produced by most animals. The intestinal tracts of many fish larvae are shorter and relatively non-functional when compared to those of adults. Larval feeding would be improved by enzyme application (Table 1), which can probably be a solution to high larval mortality in some aquatic animals. Phytase Utilization in Aquafeeds It has been confirmed in fishes that addition of phytase in diets can improve protein and amino acid digestion. The phytatelipid complex rich in metabolizable energy can be broken down in feeds by incorporation of phytase. This lowers feed costs because cheaper plant-based protein sources can be substituted for fishmeal. The inclusion of inorganic phosphorus can be drastically (CONTINUED ON PAGE 44) TABLE 1. Enzyme applications for larval fish diets. Enzyme Benefits Phytase Makes proteins and minerals like phosphorus and some trace minerals more available for animals. Lipase Promotes utilization of lipids. Cellulase Degrades cellulose containing cell walls in plants. Protease Promotes utilization of proteins from plant and animal sources. Amylase Degrades complex carbohydrates like starch and glycogen into simple sugars. Keratinase Results in the breakdown of keratin protein. Tannase Degrades the anti-nutritional factor tannin.
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