Synergistic Effects of Bacillus subtilis and Bacillus amyloliquefaciens on Growth, Immunity, Enzymatic Indices, Immune Gene Expression, and Survival of Labeo rohita Fry in a Biofloc Culture System.

Abstract

This study investigates the effects of probiotics Bacillus subtilis and Bacillus amyloliquefaciens on Labeo rohita fry within a biofloc culture system (BFC). The experimental design consisted of four treatment groups: control (BFC only), T1 (BFC + B. subtilis), T2 (BFC + B. amyloliquefaciens), and T3 (BFC + B. subtilis + B. amyloliquefaciens), each in triplicate. Molasses was added to maintain an optimal C:N ratio of 15:1. Over an 11-week period, the inclusion of probiotics resulted in significant improvements in weight gain, survival, digestive enzyme activities, and immune responses, with the T3 group showing the most pronounced effects. Probiotic supplementation significantly enhanced immune parameters, liver antioxidative activities, and expression of pro-inflammatory cytokines and antioxidant molecules, particularly in the T3 group. Additionally, there was a non-significant difference between concentration of glucose and cortisol levels in treatments and control; however, the control group showed highest glucose and cortisol among treatments. After the challenge study with Aeromonas hydrophila, the highest relative percentage survival (RPS) was observed in T3 (50%), followed by T2 (33.34%) and T1 (16.67%). These findings underscore the synergistic benefits of using a combination of probiotics in biofloc systems for enhancing the growth, immunity, and survival of L. rohita fry.