A feeding experiment was conducted in a recirculatory aquaculture system (RAS) to evaluate the effect of black soldier fly larvae meal (BSFLM)-based diet integrated with dietary methionine on growth performance, feed utilization, digestive enzyme activity and nutrient retention of local and improved African catfish (Clarias gariepinus). Six isonitrogenous diets [M0.36(0% Methionine), M0.96 (0.67% Methionine), M1.05 (0.77% Methionine), M1.15 (0.87% Methionine), M1.23 (0.97
% Methionine) and M1.41 (1.17% Methionine)] of ~35% CP each were formulated to yield methionine contents of 0.36, 0.96, 1.05, 1.15, 1.23 and 1.41%, respectively. For 84 days, the diets were fed to 1300 local and improved C. gariepinus fingerlings (initial weight 3.6±0.06 g) randomly stocked (35 fish per tank) in 36 plastic tanks.
The highest weight gain, specific growth rate, and the best feed conversion ratio were recorded from local and improved strains fed diets M1.05 and M1.15, respectively. A quadratic regression model estimated 0.94% and 0.96% as the methionine requirement for local and improved strains, respectively. The
whole-body composition for crude protein, ash, and dry matter progressively increased with increasing dietary methionine up to diet M1.41 but with simultaneous decrease in lipid content for both strains. Additionally, the protease, trypsin and lipase enzyme activities increased with increase in dietary methionine with highest activity at diet M1.41 for both strains. The amylase and alkaline phosphatase activities also increased with dietary inclusion of methionine up to diet M1.15. These finding suggest that supplementation of methionine in BSFLM- based diets could be a viable strategy for the enhancing growth performance, digestive enzymes activities and whole-body composition of C. gariepinus to ensure improved aquaculture productivity.