The effects of dietary Bacillus coagulans (MTCC 9872), Bacillus licheniformis (MTCC 6824) and Paenibacillus
polymyxa (MTCC 122) supplementation on growth performance, non-specific immunity and protection
against Aeromonas hydrophila infection were evaluated in common carp, Cyprinus carpio fry. Laboratory
maintained B. coagulans, B. licheniformis and P. polymyxa were used to study antagonistic activity against
fish pathogenic bacteria by agar well diffusion assay. Healthy fish fry were challenged by this bacterium
for determination of its safety. Fish were fed for 80 days with control basal diet (B0) and experimental
diets containing B. coagulans (B1), B. licheniformis (B2) and P. polymyxa (B3) at 109 CFU/g diet. Fish fry
(mean weight 0.329 ± 0.01 g) were fed these diets and growth performance, various non-specific immune
parameters and disease resistance study were conducted at 80 days post-feeding. The antagonism
study showed inhibition zone against A. hydrophila and Vibrio harveyi. All the probiotic bacterial strains
were harmless to fish fry as neither mortality nor morbidities were observed of the challenge. The
growth-promoting influences of probiotic supplemented dietary treatments were observed with fish fry
and the optimum survival, growth and feed utilization were obtained with P. polymyxa (B3) supplemented
diet. Study of different non-specific innate immunological parameters viz. lysozyme activity,
respiratory burst assay and myeloperoxidase content showed significant (p < 0.05) higher values in fish
fry fed B3 diet at 109 CFU/g. The challenge test showed dietary supplementation of B. coagulans,
B. licheniformis and P. polymyxa significantly (p < 0.05) enhanced the resistance of fish fry against bacterial
challenge. These results collectively suggests that P. polymyxa is a potential probiotic species and
can be used in aquaculture to improve growth, feed utilization, non-specific immune responses and
disease resistance of fry common carp, C. carpio.