Efficacy of crystalline amino acids supplementation in reduction of intact protein level in channel catfish Ictalurus punctatus diets

Abstract

A 9-week growth trial was performed to assess the role of indispensable (IAA) and dispensable amino acids (DAA) supplementation in diets designed for juvenile (10.6 g) channel catfish (Ictalurus punctatus). The effects on fish growth, feed utilization, proximate, amino acids (AA) composition, and morphometric indicators were followed. Nine iso-lipidic (8 %) experimental diets were formulated with different levels of intact protein (32, 30, 28, 26, and 24 IP) supplemented with IAA (Lysine and Histidine) to restore IAA balance to those stated in NRC (2011). Additionally, DAA (Glutamic acid and Glycine) were added to the 24IP at different rates (2 %, 4 %, 6 %, and 8 %). At the conclusion of the growth trial, however, there was a linear decrease in fish growth as IP was lowered from 32% to 24%. But, based on mean separation; final mean weight (g), thermal growth coefficient (TGC), and feed conversion ratio (FCR) of channel catfish were not significantly different (P > 0.05) among fish groups fed diets containing 32 %, 30 %, 28 % and 26 % IP supplemented with IAA. Fish growth was significantly reduced, while apparent net protein retention (ANPR) and FCR significantly increased as IP was lowered to 24%. While growth and FCR of catfish fed 24IP with DAA (2–6 %) were not significantly different compared to catfish fed 32 % and 30 %IP diets. In conclusion, IAA (lysine and histidine) could be used as a supplement to reduce intact protein from 32 % to 26 % in channel catfish diets with maintaining IAA balance as recommended by NRC (2011). Catfish growth was improved by fortification of the 24IP diet with DAA (2–6 %), so the dietary IP level could be further lowered to 24 % with supplementation of IAA and DAA.