Substitution of fish meal with enzyme‐treated soybean in diets for juvenile largemouth bass ( Micropterus salmoides )

A 63-day feeding trial was conducted to investigate the effects of enzyme-treated soybean (ESB) replacing fish meal (FM) on growth performance, muscle composition, biochemical indices, digestive enzymes activities and intestinal morphology of juvenile largemouth bass (Micropterus salmoides). Largemouth bass with initial weight of (18.14 ± 0.11) g were randomly divided into 5 groups with 3 replicates, each group of 30 fish per replicate. Five diets were formulated by replacing 0, 80, 120, 160 and 200 g kg−1 FM with ESB (ESB0, ESB80, ESB120, ESB160 and ESB200, respectively). Results showed that weight gain rate and specific growth rate significantly improved in ESB160 group (p < .05). Crude protein content in muscle significantly increased with FM replacement amount up to 160 g kg−1, while crude lipid content significantly decreased (p < .05). Activities of lysozyme and catalase reached the highest level in ESB120 group (p < .05). The activity of superoxide dismutase was significantly increased in ESB200 group, while malondialdehyde concentration significantly decreased. With increasing dietary ESB level, activities of protease and lipase in stomach had significant increase in ESB160 group (p < .05). The intestinal wall thickness and villi length in ESB160 group were significantly higher than those in other groups (p < .05). To sum up, the present study suggested that the optimal replacement level of dietary FM by ESB was 160 g kg−1, which means the supplemented levels of FM and ESB in diet were 400 and 260 g kg−1, respectively.