lysine and methionine supplementation in high soy protein content diets for silvery-black porgy (sparidentex hasta) juveniles

A two-month feeding trial was conducted to evaluate the effect of partial replacement of fish meal (fm) by soybean protein (sp) alone or in combination with lysine (lys) and methionine ( met) supplementation in practical diets for silvery-black porgy juveniles (16.7±0.1 g). seven isoproteic (ca. 50% crude protein) and isoenergetic (ca. 22.4 mj kg^-1) diets were formulated in which 45% (sp45), 60% (sp60) and 75% (sp75) of fm protein were replaced by sp and the control diet (fm) was prepared with fm as the major source of protein. in sp45+, sp60+ and sp75+ diets, 45 to 75% of fm was replaced by sp with supplementing blends of lys and met. growth performance, feed utilization, and protein and lipid digestibility decreased with increasing dietary sp levels (p<0.05). fish fed sp75 had the highest whole body lipid content, but with the lowest whole body arginine, lysine, histidine, phenylalanine and taurine concentrations (p<0.05). supplementing lys and met in sp based diets did not improve growth performance, suggesting that the anti-nutritional factors in soybean protein products rather than met and lys deficiency might limit fm substitution with sp in silvery-black porgy juveniles.