Partial replacement of fish meal by enzymatically hydrolyzed soybean does not adversely impact the growth performance, antioxidant capacity, immunity and intestinal health of the juvenile Eriocheir sinensis

An 8-week experiment was conducted to study the effect of dietary enzymatic hydrolysis of full-fat soybean (ESB) in combination with fish meal (FM) on the growth performance, oxidation resistance, immunity and intestinal health of juvenile Chinese mitten crab Eriocheir sinensis. The crabs (0.74±0.01 g) were randomly divided into six groups. Six diets were formulated by replacing 0, 15, 30, 45, 60 and 75% of FM (350 g/kg) with ESB (ESB0-control, ESB15, ESB30, ESB45, ESB60 and ESB75, respectively). The weight gain rate and specific gain rate of the crabs were significantly greater in the ESB15 group than in the control group, while they decreased significantly with replacement levels up to 60%. A replacement level of 15% significantly improved the hepatopancreas antioxidant capacity and hemolymph acid phosphatase indices. However, the glutathione peroxidase activity and total antioxidant capacity in the hepatopancreas decreased significantly when the replacement concentration reached 45% and 75%, respectively. The replacement level could increase to 45% without affecting the hepatopancreas malondialdehyde content. Hemolymph acid phosphatase and alkaline phosphatase activities decreased significantly with replacement levels up to 60%. Aspartate aminotransferase activity in the hemolymph increased significantly when the replacement dose reached 75%. Moreover, different replacement levels did not affect the gene expression of the hepatopancreas ALF1/2, crustin, relish, or LITAF. The hepatic mRNA levels of TLR2 and Myd88 were significantly elevated in the ESB45 and ESB60 groups, respectively. Unlike those in the ESB0 group, intestinal PM1 and PM2 expressions were significantly higher in the ESB15 group. In contrast, intestinal PM1, PM2 and PT expressions were significantly lower in the ESB60 and ESB75 groups. The present study suggests that 15% of the optimal replacement level of FM with ESB enhanced growth performance, antioxidation, immunity and intestinal health. To maintain normal growth performance, the replacement level of FM with ESB could not exceed 45%.