Bacillus subtilis and Bacillus licheniformis in diets for Nile tilapia ( Oreochromis niloticus ): Effects on growth performance, gut microbiota modulation and innate immunology

This study aimed to verify the possible positive effects of feeding the commercial probiotic Bioplus 2BC® [Bacillus subtilis (1.6 × 1010 CFU/g) and Bacillus licheniformis (1.6 × 1010 CFU/g)] to Nile tilapia on its growth performance, nutrient digestibility, gut microbiology, haematology (hematimetric index, erythrocyte, leucocyte and thrombocyte counts) and innate immunology (lysozyme, burst respiratory and phagocyte activities). For this purpose, one in vivo assay was performed following a completely randomized design, with four treatments (0.00%; 0.02%; 0.04%; and 0.08% of probiotic inclusion on ratio) and four replicates. The fish fed with diets containing 0.04% and 0.08% of probiotics presented higher weight gain than the control group, as well as higher thrombocyte counts in the bloodstream. The positive effect of the probiotics on the gut microbiota was illustrated by the higher richness and habitability indexes, soaring genetic variability. On the contrary of control, the groups fed with probiotic had Firmicutes, Fusobacteria and Bacteroidetes phyla, and a lower percentage of Proteobacteria. The inclusion of 0.04% and 0.08% of B. subtilis and B. licherniformis in the fed provides better growth performance and modifies the intestinal microbiota, reducing the class of potential pathogen agent species. The establishment of a beneficial microorganism population may improve host health.