Probiotic applications of two dominant gut Bacillus strains with antagonistic activity improved the growth performance and immune responses of grouper Epinephelus coioides

The effect of dietary administration of Bacillus pumilus and Bacillus clausii, the dominant bacteria with antagonistic activity in the gut of fast growing fish, on the growth performance and immune responses of grouper Epinephelus coioides were assessed. The fish were fed for 60 days with three different diets: control (without probiotics), diet T1 supplemented with 1.0 × 108 cells g−1 B. pumilus, diet T2 with 1.0 × 108 cells g−1 B. clausii. No significant improvements of weight gain or specific growth rate were observed in the probiotic fed groups, but a significant improvement of feed conversion ratio was observed after 60 days of feeding. Phagocytic activity and phagocytic index of fish fed probiotic diets were significantly higher than those of fish fed the control diet for 60 days. Superoxide dismutase (SOD) concentrations showed no significant difference between the treatments and the control during the whole experiment period, but which increased by 11.4% and 18.5% after 60 days of fed with diets T1 and T2, respectively. The serum lysozyme activities of fish fed diets T1 and T2 were significantly higher than that of fish fed control diet, and had respectively increased by 34.7% and 17.4% compared to the control after 60 days of feeding. Serum complement C3 levels of the treatments were significantly higher than that of control after 30 days of feeding, but no significant difference in serum complement C3 and C4 levels were observed between the treatments and the control after 60 days of feeding. The serum IgM levels of fish fed diet T1 and diet T2 were higher than that of fish fed control diet, and significant increase was observed in fish fed diet T2 for 30 days. The results demonstrated potential for B. pumilus and B. clausii to improve growth performance and immune responses of E. coioides.