Total sulfur amino acid requirement and its application to practical diets for juvenile tilapia (Oreochromis spp.)

Abstract

Tilapia have become one of the most important fish species for aquaculture and play an increasing role in the international aquatic food trade. Therefore, the development of cost-effective feeds using inexpensive and locally available plant and animal protein sources will contribute to sustainable aquaculture development for the future. Three separate studies, each contained two feeding experiments, were conducted to evaluate practical applications of various protein sources in grow-out diets, to determine total sulfur amino acid (TSAA) requirement and replacement of cystine for methionine in semi-purified diets and to determine and confirm methionine requirement in practical diets for juvenile tilapia (Oreochromis spp.). Results of the first study showed that dehulled solvent-extracted soybean meal (DSESM) and expeller pressed soybean meal (EPSM) could totally replace fish meal’s inclusion rate in commercial diets for juvenile tilapia (Oreochromis spp.) and methionine did not appear to be limiting in practical diets using cottonseed meal (CSM), meat and bone meal (MBM) and DSESM as primary protein sources. To further optimize practical diets with respect to TSAA, the second study was conducted to more precisely determine TSAA requirement and replacement value of cystine for methionine of juvenile Nile tilapia in semi-purified diets. Broken-line regression analysis on weight gain data indicated that the TSAA requirement of juvenile Nile tilapia was 0.85% of the diet or 3.04% of dietary protein and cystine could replace up to 49% of methionine requirement based on an equimolar sulfur basis. This means methionine requirement of juvenile Nile tilapia was 0.43% of the diet or 1.54% of dietary protein. It is important to utilize methionine requirement value determined by semi-purified diets in the formulation of practical diets to determine and confirm the practical application of methionine requirement data. Hence, the last study was conducted to determine and confirm methionine requirement in practical diets for juvenile Nile tilapia (O. niloticus). Results of the last study indicated that methionine requirement of juvenile Nile tilapia was 0.49% of the diet or 1.75% of dietary protein. Furthermore, methionine appeared to be limiting when a portion of DSESM was replaced by gelatin and methionine supplementation did not have positive effects on weight gain, survival or feed efficiency ratio (FER) of juvenile Nile tilapia fed diets using CSM and DSESM as protein sources.