Dietary methionine requirement of Indian major carp fry,Cirrhinus mrigala (Hamilton) based on growth,feed conversion and nitrogen retention efficiency

This study was aimed at quantifying methionine requirement of Indian major carp fry, Cirrhinus mrigala (2.2 ± 0.2 cm; 0.19 ± 0.02 g) by conducting a 12‐week feeding trial. Casein–gelatine‐based isonitrogenous (40 g 100 g^?1 crude protein) and isoenergetic (15.42 kJ g^?1 DE) amino acid test diets were prepared to contain six levels of l ‐methionine (1.1, 1.3, 1.5, 1.7, 1.9 and 2.1 g 100 g^?1 dry diet) at a fixed level of cysteine (0.85 g 100 g^?1 dry diet) and fed to apparent satiation thrice daily to triplicate groups of fish. When absolute weight gain (g per fish), feed conversion ratio, protein deposition (g per fish) and nitrogen retention efficiency data were subjected to broken‐line and second‐degree polynomial regression analysis, 95% of the plateau of above parameters was achieved at dietary methionine concentrations between 1.60 and 1.69 g 100 g^?1 dry diet or 0.10 to 0.11 g methionine kJ^?1 DE, corresponding to 4.1–4.22 g 100 g^?1 protein or 0.44–0.47 g methionine kJ^?1 DE. Based on these results, dietary methionine requirement of fry C. mrigala is recommended 1.60–1.69 g 100 g^?1 diet or 0.10–0.11 g methionine kJ^?1 DE.