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ABSTRACT
In the recent years, replacement of fishmeal with plant-based protein ingredients is the priority area of research in the globally expanding aquaculture industry. However it brings in issues of poor digestion and low feed efficiency because of the presence of anti-nutritional factors (ANTs), nonstarch polysaccharides (NSPs) and trypsin inhibitors in vegetable protein sources. Exogenous enzyme supplementation besides digesting these anti nutritional factors also helps in better digestion and utilization of nutrients in aqua feeds, improving FCR and reducing water pollution. Most commonly used enzyme additives are phytase, carbohydrases like a-amylase, ß-mannanase, a-galactosidase, xylanase, cellulase and pectinase, protease and lipase to a small amount. In this regard, focus needs to be given on the feed processing methods for the efficient enzyme delivery system to increase their thermal tolerance. This paper provides an overview on the importance of enzyme supplementation, commonly used enzyme supplements, issues to be addressed along with a note on thrust areas of research.
Keywords: Feed additives, Enzyme supplements, Anti-nutritional factors (ANTs), Nutrient digestibility and Low pollution feeds.
INTRODUCTION
Fish production from feed-dependent aquaculture has increased from 12.2 million tonnes in 1995 to 50.7 million tonnes in 2015. The aqua feed industry is responding well to this growing demand with a record volume of 47.7 million tonnes of industrial aquafeed produced in 2015 and is now the largest user of fishmeal and fish oil (Hasan, 2017). The feed industry is trying to address this issue by the use of suitable additives like enzymes that allow replacing fish meal with plant protein sources.
Enzyme supplements are either single, purified enzymes or crude enzyme preparations containing multiple enzymes added to fish feeds to enhance the digestion of feed components that the fish cannot digest either completely or efficiently. The use of exogenous enzymes as feed additives to improve nutrient digestibility of plant-based feedstuff has been researched extensively in poultry and swine. In aquaculture, the use of enzyme supplements has emerged quite recently.
The important enzymes used in fisheries feed industry are phytase, carbohydrase, protease and lipase. The primary purpose of enzyme application in feeds is to improve digestion. In the case of fishes or shrimps lacking certain enzymes even in adulthood, application of these enzymes results in better utilization of nutrient fractions (Fish, 1960;...