Dietary leucine requirement of fingerling Catla catla (Hamilton) based on growth, feed conversion ratio, RNA/DNA ratio, leucine gain, blood indices and carcass composition

This study aimed at quantifying leucine requirement of fingerling Catla catla [3.75 (mean body length) +/- A 0.15 (SE) cm, 0.66 (mean body weight) +/- A 0.04 (SE) g] by conducting a 12-week feeding trial. Six casein- and gelatin-based (33 % crude protein, 14.0 kJ g(-1) calculated digestible energy) semipurified diets containing different concentrations of leucine (0.73, 0.97, 1.24, 1.46, 1.74 and 1.97 % dry diet) were fed to triplicate groups of fish to apparent satiation thrice daily at 08:00, 12:30 and 17:30 hours. Maximum absolute weight gain (AWG, 7.45 g fish(-1)), protein gain (PG, 1.31 g fish(-1)), leucine gain (LG, 85.33 mg fish(-1)), RNA/DNA ratio (4.62) and best feed conversion ratio (FCR, 1.51) were recorded at 1.74 % dietary leucine. Hemoglobin, hematocrit and red blood cell counts count were also found to be optimum in fish fed diet with 1.74 % leucine. Quadratic regression analysis at 95 % maximum response of AWG and minimum response of FCR against dietary leucine concentrations reflected the requirement at 1.58 and 1.57 % dry diet, respectively. Based on above results, inclusion of leucine ranging from 1.57 to 1.58 % of the dry diet is recommended for developing leucine-balanced commercial feeds for the intensive culture of C. catla.