Effects of host-associated probiotic Bacillus altitudinis B61-34b on growth performance, immune response and disease resistance of Nile tilapia (Oreochromis niloticus) raised under biofloc system

This investigation was performed to assess the influences of the host-associated probiotic Bacillus altitudinis B61-34b (BAA) on growth, immune response and disease resistance to Streptococcus agalactiae in Nile tilapia (Oreochromis niloticus). Fish (25.50 +/- 0.52 g fish(-1)) were distributed into 15 aquaria (150 litres tank(-1)) at density of 20 fish tank(-1). The fish were fed basal diets with BAA inclusions in different concentrations: 0 (BAA1-Control), 10(6) (BAA2), 10(7) (BAA3), 10(8) (BAA4) and 10(9) (BAA5) CFU ml(-1) for 8 weeks. A completely randomized design with three replications was used. The results indicated that BAA administration generated greater (p < 0.05) skin mucus and peroxidase activities compared to the control, with maximum levels recorded in BAA4 and BAA5. Higher serum immunities, such as serum lysozyme, serum peroxidase, complement, phagocytosis and respiratory burst activities were observed in the BAA4 and BAA5 dietary groups compared to the control, BAA1, BAA2 and BAA3 diets. The relative percentage of survival, growth performance and FCR were also significantly higher (p < 0.05) in the BAA4 and BAA5 groups. In conclusion, dietary supplementation of B. altitudinis at 10(8) CFU ml(-1) can improve Nile tilapia's growth performance, skin mucus and serum immunities, and disease resistance.