Aqua Feed Proteins

Essential Role and Significance of Proteins in Aquafeed

Aquafeed is a formulated, complete feed supplied to aquatic animals in pisciculture, especially to fishes, shrimps and crabs. About 5% of aquafeed are more protein rich in comparison to feed for terrestrial animals. A typical formulated commercial diet for tilapia or catfish contains approximately 32-40% proteins, while that for trout or salmon contains as high as 44-50% proteins. The percent content of protein is determined on the basis of dry weight of the aquatic animals. In contrast, commercially formulated diet for terrestrial animals rarely exceeds 20% in total proteins. This is because some aquatic species like salmon and trout derive their required energy more efficiently from protein source than doing the same from carbohydrate.

Protein is the most costly nutrient among the aquafeed ingredients. Depending on the specific requirement of the aquatic species, the type and quantity of protein is determined in aquafeed. An ideal protein in fish meal provides optimum balance of amino acids, which is required for maximum growth and superior performance. It is better to formulate the aquafeed based on ideal protein content as this provides the best way of using lesser amount of protein to meet the amino acid requirement of the fish diet.

Amino acids are the building blocks of all proteins. Among 200 natural amino acids, twenty are most abundant in aquafeed proteins. Ten of them must be supplied with fish feed, as they cannot be synthesised in fish body. These ten amino acids are: lysine, leucine, isoleucine, phenylalanine, tryptophan, methionine, valine, arginine and histidine. Fish feeds prepared from plant proteins are generally extracted from soya, peas, beans and gluten from wheat and maize. Processed Animal Proteins (PAPs) are used as an alternative protein source in aquafeed.

Animal proteins in aquafeed contain most of the essential amino acids, except methionine. These are exceptionally high in arginine and other water soluble amino acids, which act as palatant and attractant for fishes. Drying methods and other raw materials added to aquafeed play important role for this varying digestibility levels of aquafeed. Higher the quality of aquafeed is, higher will be its digestibility. Poultry meals and ruminant proteins in aquafeed are used commonly to obtain cheaper fish meals.

Protein requirements are generally higher for smaller fishes, while the requirement for protein reduces with the increased size of fishes. The requirement for protein also varies with difference in water quality and temperature. Genetic composition and feeding rates of fish also control the variations in requirement for protein. Along with proteins, adequate amount of carbohydrate and fat should also be present in fish feed to maintain proper growth and health. In absence of proper ratios of carbohydrate and fat, protein acts as energy and life support for aquatic animals, rather than helping in growth.

Fish and shrimps are able to utilize as much as 65% of the protein from the fish feed, while rest is lost to the environment. Nitrogen present in amino acids is excreted as ammonia through the fish gills, while 10% of this natural element is lost as solid wastes. This is why waste management practice is also important in fish farming for maintaining the water quality and fish health along with keeping the environment free of pollution.

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