In this study, Bacillus subtilis natto was evaluated on the growth, digestive enzyme activity, oxidative status, Intestinal bacteria, non-specific immune response and the growth-related genes’ expression in the skeletal muscle of Japanese Flounder. Fish fed five different levels of B. s. natto powder at 0 (BN0), 0.01 (BN1), 0.10(BN2), 1.00(BN3) and 10.00(BN4) g/kg diet for 60 days.
The ?sh of BN3 and BN4 groups displayed better growth performance and specific growth rate than the BN0 groups (P < 0.05). B. s. natto supplementation significantly improved the specific activities of amylase, protease and lipase enzymes when compared to the control group (P < 0.05). Furthermore, hemoglobin and the nitro blue tetrazolium values up regulated significantly upon B. s. natto, especially in case of BN3 and BN4 diets (P < 0.05). Serum peroxidase activity enhanced significantly in fish fed BN2 and BN3 diets (P < 0.05). When compared to the control, the number of Bacillus, Lactobacillus and total bacteria in intestinal were significantly increased. The speci?c growth rate analysis and expressional regulation of the growth-related genes stimulated by B. s. natto suggest the potential application of B. s. natto in improving the growth performance on the Japanese Flounder. Additionally, the supplementation of B. s. natto in the diet of Japanese Flounder at 1.00 and 10.00 g/kg diet could improve the growth, feed utilization, health condition and immune response.