Effect of dietary phenylalanine levels on growth, hemato-biochemical composition and tyrosine replacement value for phenylalanine in stinging catfish Heteropneustes fossilis -Bloch 1974 fingerling

Two 10-week feeding experiments were conducted to determine the total aromatic amino acid requirement and tyrosine (Tyr) replacement value for phenylalanine (Phe) for fingerling Heteropneustes fossilis by feeding casein + gelatin based amino acid test diets [400 g/kg crude protein (CP); 17.90 MJ/ kg gross energy (GE)]. In experiment 1, Phe was determined by feeding six test diets containing graded levels of Phe (4.5-14.5 g/kg diet, as fed) with 6.0 g/kg Tyr fixed and fed in triplicate groups of 20 fish each in 60-L troughs fitted with continuous flow-through. Significantly (P < 0.05) highest live weight gain (LWG%), best-feed conversion ratio (FCR), highest protein efficiency ratio (PER) and body protein deposition (BPD) was reported at 10.5 g/kg dietary Phe with constant level of Tyr 6.0 g/kg fed group. Quadratic regression analysis of live weight gain, FCR, PER and BPD data indicated Phe requirement at 11.08, 10.75, 10.45 and 10.45 g/kg of diet, respectively. Based on the above results, Phe requirement of H. fossilis is recommended at 10.8 g/kg of diet. A second experiment under similar experimental design was conducted containing graded levels of Tyr (2.1-12.1 g/kg diet, as fed) with 10.8 g/kg Phe fixed in all the diets to determine the replacement value of Tyr for Phe. Significantly (P < 0.05) highest LWG %, best-FCR, PER and BPD values were obtained at 8.1 g/kg dietary tyrosine level. Quadratic regression analysis of LWG%, FCR, PER and BPD data indicated Tyr requirement at 8.7, 8.7, 8.05 and 8.05 g/kg of diet, respectively. The above results suggest that 8.4 g/kg Tyr, corresponding to 21.0 g/kg of protein would be useful for optimum growth of H. fossilis at fingerling stage and the replacement value of Tyr for Phe is 43.75% on weight and 39.89% on molar basis. Thus, the total aromatic amino acid requirement was recommended to be 19.2 g/kg of diet, corresponding to 48.0 g/kg of protein for optimum growth of H. fossilis.