Total sulfur amino acid requirement and cystine replacement value for fingerling stinging catfish, Heteropneustes fossilis (Bloch)

Abstract

Abstract Heteropneustes fossilis is found in most of the Asian countries and has high consumer demand due to its recuperative and medicinal qualities. Being a lean fish with high iron content, it is recommended to people suffering from anemia and cardiac diseases. In view of the above, two 8-week feeding trials were conducted to determine total sulfur amino acid requirement (TSAA) and cystine replacement value for fingerling Singhi, H. fossilis . In experiment I, six casein gelatin based isonitrogenous (380 g kg − 1 CP) and isocaloric (17.9 MJ kg − 1 GE; 15.3 MJ kg − 1 DE) amino acid test diets with graded levels of methionine (6.5, 8, 9.5, 11, 12.5, and 14 g kg − 1 of the dry diet) were prepared. Cystine was maintained at 4 g kg − 1 in all the diets. The diets were fed to quadruplicate groups of randomly assigned fingerlings (6.9 ± 0.1 g; 10.9 ± 0.2 cm) to apparent satiety twice daily at 28 °C water temperature in a flow-through system (1–1.5 L min − 1 ). Based on the quadratic regression analysis at 95% maximum and minimum response of absolute weight gain (AWG g fish − 1 ), feed conversion ratio (FCR), protein deposition efficiency (PDE%), energy deposition efficiency (EDE%), RNA:DNA ratio and methionine retention efficiency (MRE%), methionine requirements were found to range between 10.3 and 10.7 g kg − 1 of dry diet, corresponding to 27.1–28.2 g kg − 1 of the dietary protein. Hence, TSAA requirement was found to be 14.7 g kg − 1 of the dry diet (10.7 g kg − 1 methionine + 4 g kg − 1 cystine). To find out the cystine replacement value for methionine, six diets with various ratios of methionine:cystine (90:10, 80:20, 70:30, 60:40, 50:50, and 40:60) on equimolar sulfur basis as per the TSAA requirement determined in experiment I (14.7 g kg − 1 ) were prepared and fed to fingerling H. fossilis (7.2 ± 0.2 g; 11.3 ± 0.1 cm) under identical laboratory conditions. The quadratic regression analysis of AWG g fish − 1 , FCR, PDE%, EDE%, RNA:DNA ratio and MRE% at 95% maximum and minimum quadratic response projected that cystine could replace from 39.6 to 40.2% of methionine requirement on an equimolar sulfur basis without hampering growth. On the basis of the above results, the total sulfur amino acid requirement of the H. fossilis is recommended to be 14.7 g kg − 1 dry diet (7.1 g kg − 1 methionine + 7.6 g kg − 1 cystine) of which 39.9% was spared by cystine.