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.

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