Effects of Dietary Supplementation of DL-Methionine on Growth and Whole Body Amino Acid Profile of Genetically Improved Farmed Tilapia

A 60-day indoor growth trial was conducted to study the effects of dietary DL-methionine supplementation on the growth performances and survival of GIFT tilapia. Five corn-soy based isonitrogenous and isoenergetic experimental diets (32% crude protein) were formulated with graded levels of methionine (% of dry diet) viz., T0 (0.75), T1 (0.9), T2 (1.05), T3 (1.2) and T4 (1.35%). The feeding trial in triplications was conducted using 15 nos. of 1 X 1 X 1.5 m sized cages installed inside the indoor tanks. Among the experimental diets T1, a diet containing methionine level of 0.9% of dry diet yielded significantly (p <0.05), higher mean body weight gain (51.56 +/- 0.23 g) followed by T0 (45.2 +/- 0.49 g), T2 (42.58 +/- 0.10 g), T3 (37.33 +/- 0.06 g) and T4 (30.87 +/- 0.13g). The best results in terms of feed conversion ratio (1.12 +/- 0.08), specific growth rate (1.76 +/- 0.01), feed efficiency ratio (0.89 +/- 0.06) and protein efficiency ratio (1.60 +/- 0.01) were observed in T1. Whole body moisture and lipid contents did not affect dietary methionine supplementation. However, the whole body protein content was significantly (p <0.05) enhanced in fish fed methionine at 0.9% of the dry diet. There was no effect of treatments on whole body essential and non-essential amino acid profiles except lysine, methionine and tryptophan. The results demonstrated that the dietary methionine requirement in corn-soy based diet for GIFT tilapia would be 0.9% of the dry diet for better growth performances.