Supplementation of autochthonous potential probiotic Bacillus subtilis COFCAU_BSP3 to Labeo rohita feed: effect on immune-biochemical responses and resistance against Aeromonas hydrophila

The present investigation examined the potential of a previously identified probiotic derived from the intestinal tract of Labeo rohita to modulate the immune system and confer disease resistance when included in a basic diet. The viability of B. subtilis in the feed was assessed at both 4 °C and 28 ± 2 °C, revealing no notable changes. A total of 180 L. rohita fingerlings (19.27 ± 1.96 g) were randomly distributed in four groups (one control and three probiotic-treated groups in triplicate) and fed with the basal (the control) and B. subtilis–supplemented diets (at a concentration of 107, 108, and 109 CFU g−1) over a period of 20 days. Immunological responses, biochemical parameters, and immune-relevant gene expression (interleukin 1β (IL-1β), interferon 1γ (IFN-1γ)) relevant to immunity were analyzed on the 0, 10th, and 20th day post-feeding. In a separate but similar setup, probiotic-fed fish were intraperitoneally challenged with Aeromonas hydrophila (ATCC 7966), and their post-challenge survivability was calculated. After the 20-day feeding period, a significant (P < 0.05) improvement in immune-biochemical response and immune gene expression was evident. Serum glucose and sodium 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 L. rohita, thereby highlighting the potential of B. subtilis COFCAU_BSP3 as a beneficial probiotic for aquaculture.