The influences of Bacillus subtilis C-3102 inclusion in the red sea bream diet containing high levels of soybean meal on growth performance, gut morphology, blood health, immune response, digestibility, digestive enzymes, and stress resistance

This study evaluated the effects of replacing fish meal with dehulled soybean meal (SBM) with and without Bacillus subtilis in red sea bream diets. Five diets with dehulled SBM as a replacer for fish meal protein at 0 (FR0), 500 g kg(-1) (FR50), 750 g kg(-1) (FR75), 500 g kg(-1) + 1 g B. subtilis (FRB50), and 750 g kg(-1) + 1 g B. subtilis (FRB75) were formulated. FRB50 showed a marked increase in the growth performance parameters, whereas FR75 showed the lowest values. Interestingly, digestibility parameters were significantly enhanced in FRB50 and FRB75. FR0 and FRB50 groups showed the highest body protein content, whereas FR50 and FRB50 groups showed the highest lipid content. The intestines exhibited increased villi, enterocyte, and microvillus height in FR0, FRB50, and FRB75. FR0, FRB50, and FR50 groups showed high antioxidant potential than control and other groups. Respiratory burst activity showed significant enhancement in FRB50 and FRB75 groups. Also, fish fed on FRB50 displayed a high level of activity in immune-related enzymes. Low salinity stress resistance increased significantly with FRB50 groups, whereas FR75 showed the lowest value. In this work, dietary B. subtilis increased the inclusion of dehulled SBM without affecting red sea bream growth, digestion capacity, immunity, or health status.