Total sulphur amino acid requirement and maximum cysteine replacement value for methionine for fingerlingCatla catla(Hamilton)

Abstract

Two separate 12 weeks feeding trials were performed to quantify the total sulphur amino acid (TSAA) requirement (experiment I) and cysteine replacement value for methionine (experiment II) of fingerling Catla catla. In experiment I, six casein–gelatin based (33% crude protein; 16.72 kJ g−1 gross energy) diets with graded levels of TSAA (0.56%, 0.81%, 1.06%, 1.31%, 1.56%, 1.81% dry diet) were fed to triplicate groups of fish (3.55 ± 0.06 cm; 0.65 ± 0.02 g) near to satiation. The TSAA requirement was determined by quadratic regression analysis of absolute weight gain (AWG), protein efficiency ratio (PER), feed efficiency (FE), protein gain (PG) and TSAA gain (TSAAG) against dietary TSAA concentrations at 95% maximum response. Above analysis revealed that inclusion of TSAA at 1.28% dry diet (1.22% methionine + 0.06% cysteine), corresponding to 3.87% of dietary protein is optimum. In experiment II, to determine the replacement value of cysteine for methionine, six diets containing 1.28% TSAA determined in experiment I with different ratios of l-methionine and l-cysteine (80:20, 70:30, 60:40, 50:50, 40:60, 30:70) on equimolar sulphur basis were fed to fish (3.65 ± 0.08 cm; 0.67 ± 0.04 g). Broken-line regression analysis of AWG, PER, FE, PG and TSAAG against varying methionine to cysteine ratios yielded the optimum cysteine replacement value at 40.3%. Based on above analysis, it is recommended that inclusion of 1.28% dietary TSAA, corresponding to 3.87% of dietary protein is optimum of which 40.3% could be spared by cysteine. Data generated during this study would be useful in formulating TSAA balanced, cost-effective feeds for the intensive culture of this fish.