Total aromatic amino acid requirement of the Indian major carp, Cirrhinus mrigala (Hamilton-Buchanan)

Quantification of the essential amino acid requirements of a species is required for formulating optimal diets for cultivated fish. In this study, crystalline L-phenylalanine was used to determine the quantitative phenylalanine requirement of juvenile Cirrhinus mrigala. Test diets (40% crude protein) contained vitamin-free casein and gelatin supplemented with crystalline L-amino acids to provide an amino acid profile similar to C. mrigala muscle protein except for phenylalanine. Diets containing six graded levels of L-phenylalanine (0.80, 1.10,1.40, 1.70, 2.00 and 2.30%) and a fixed level of tyrosine (0.52%) were formulated and fed to triplicate groups of C. mrigala juveniles twice a day at a rate of 10% of the fish body weight per day for 56 days. The optimum dietary requirement for phenylalanine, estimated by breakpoint regression analysis, was 1.75% of the diet (4.38% of the dietary protein) or 2.27% of the total aromatic amino acid (5.68% of the dietary protein). Beyond the optimum level, phenylalanine significantly depressed growth. The best feed efficiency, specific growth rate and survival were obtained with the diet containing close to the optimum level of aromatic amino acid.