Effects of potential probiotic Bacillus amyloliquifaciens FPTB16 on systemic and cutaneous mucosal immune responses and disease resistance of catla (Catla catla)

• Bacillus amyloliquifaciens FPTB16 was studied as probiotic on catla immunity and disease resistance.
• Systemic and cutaneous mucosal immune responses were enhanced after probiotic administration.
• The probiotic improved the survival of catla against Edwardsiella tarda challenge.
• Optimal dietary dose of B. amyloliquifaciens was 109 CFU/g diet.

Effects of dietary administration of Bacillus amyloliquefaciens FPTB16 on systemic and mucosal immunity and disease resistance of catla (Catla catla) against Edwardsiella tarda infection were evaluated in the present study. The laboratory maintained B. amyloliquefaciens was used to study antagonistic activity against fish pathogenic bacteria by agar well diffusion assay. Healthy catla were challenged by this bacterium for determination of its safety. For preparation of probiotic supplemented diet, the bacteria were added to the basal diet (control) at three different inclusion levels i.e., 1 × 109, 1 × 108 and 1 × 107 CFU/g diet. Fish (weight 25–30 g) were fed with these diets and various immune parameters and disease resistance study were conducted at 4 weeks and 8 weeks post-feeding. The bacterial antagonism study showed inhibition zone against E. tarda, Aeromonas hydrophila, Vibrio parahaemolyticus and V. harveyi. B. amyloliquefaciens was harmless to catla as neither mortalities nor morbidities were observed after the challenge. Study of different systemic and mucosal immunological parameters viz. superoxide anion production and nitric oxide production, myeloperoxidase content, lysozyme activity and total protein content showed significant enhancement (p < 0.05) in fish fed with 108 and 109 CFU/g B. amyloliquefaciens at both time points with the highest values observed in case of 109 CFU/g. For fish fed with 107 CFU/g B. amyloliquefaciens, all the parameters showed significant enhancement (p < 0.05) at both time points except the lysozyme activity of serum at 8 weeks. Diet containing 108 and 109 CFU/g B. amyloliquefaciens significantly enhanced (p < 0.05) the resistance of catla against bacterial challenge at both time points. These results collectively suggest that B. amyloliquefaciens is a potential probiotic species and can be used in aquaculture to improve health status and disease resistance with an optimal dietary supplementation of 109 CFU/g.