efficacy of dietary supplementation with endogenous bacillus subtilis on growth performance, immune response and gene expression of juvenile rainbow trout (oncorhynchus mykiss)

Potential of a host-associated probiotic, bacillus subtilis, was successfully screened from 6 isolates from the intestines of healthy rainbow trout (o. mykiss) based on multiple probiotic characteristics in vitro assays, such as, hemolytic activity, biofilm formation, extracellular enzyme activity, inhibitory activity against pathogens, physicochemical tolerance to gastrointestinal stress, cell surface hydrophobicity, autoaggregation, and antibiotic susceptibility. a total of 450 o. mykiss fingerlings were randomly distributed in three groups (one control and two probiotic-treated groups in triplicate) and fed with the basal (the control) and b. subtilis–supplemented diets (at a concentration of 5×107 and 108 cell/ml b. subtilis, over a period of 60 days. after eight weeks of feeding trial revealed that dietary supplementation of b. subtilis 6 at all two concentrations (5×107 and 108 cell/ml of b. subtilis) immunological responses, biochemical parameters, antioxidant parameter and immune-relevant gene expression (interleukin 1β (il-1β), hsp70 and tgf-β))) relevant to immunity were analyzed on the 30th, and 60th day post-feeding. after the 60-day feeding period, a significant (p<0.05) enhancement in some immune-biochemical response and immune gene expression was evident. serum ast, alt levels exhibited a significant (p<0.05) decrease. the inclusion of b. subtilis in the diets led to a substantial (p<0.05) increase in the survival of a. hydrophila–challenged o. mykiss, thereby highlighting the potential of b. subtilis as a beneficial probiotic for aquaculture in short-time period.