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

Abstract

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.