Effects of soy protein base diet supplemented with lysine and methionine on digestive enzymes activity and hematological parameters in silvery-black porgy (Sparidentex hasta) juveniles

The effect of dietary partial replacement of fish meal (FM) with soybean protein (SP) alone or in combination with lysine (Lys) and methionine (Met) supplementation were tested in a 60-day feeding trial for silvery-black porgy (Sparidentex hasta) juveniles. 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 (98% of purity). The activities of the trypsin, lipase and α-amylase were higher in fish fed SP diets with crystalline amino acids supplementation than in the other groups (p<0.05). Fish fed SP75 and SP75+ diets had the lowest red blood cell count and hematocrit level (p<0.05). The results of the current study indicated that anti-nutritional factors in a soy-protein based diet rather than lysine and methionine deficiencies may have adverse effects on digestive enzymes activities and health condition in silvery-black porgy juveniles.