Probiotic Bacillus licheniformis competitively establishes and enhances production efficiency, immune responsiveness, and protection against Aeromonas hydrophila O:18 in Cirrhinus mrigala (Ham.)

The use of probiotics is increasingly becoming a strategic tool in aquaculture production systems to mitigate the impacts of antimicrobial resistance. The effects of dietary Bacillus licheniformis on the immune response and disease resistance of Cirrhinus mrigala were investigated following a 30-day growth trial. One hundred eighty fingerlings (10 ± 2 g) were randomly assigned to five groups (three replicates each) and fed either a control diet or diets supplemented with B. licheniformis at 1.0 × 10⁶ cfu g⁻ 1 (BL-6), 0.5 × 10⁷ cfu g⁻ 1 (BL-05.7), 1.0 × 10⁷ cfu g⁻ 1 (BL-7), or 0.5 × 10⁸ cfu g⁻ 1 (BL-8). Probiotic supplementation significantly (P < 0.05) improved weight gain percentage, specific growth rate, and feed conversion ratio. B. licheniformis at 10⁷ cfu g⁻ 1 and higher competitively replaced and decreased Gram-negative rods (from >75% to