The effect of biofloc density and Bacillus sp. NP5 supplementation on bacterial inhibition, antibiofilm activity, and the immunity of the Pacific white shrimp (Penaeus vannamei) against Vibrio parahaemolyticus

This study aimed to evaluate the effect of biofloc density supplemented with Bacillus sp. NP5 on bacterial inhibition, antibiofilm activity, growth performance, and the immune response of Pacific white shrimp ( Penaeus vannamei ) against Vibrio parahaemolyticus , and to determine the optimal biofloc density for disease resistance in shrimp aquaculture. Biofloc was prepared with molasses as a carbon source (C/N 10) and supplemented with Bacillus sp. NP5 (10⁶ CFU/mL). Shrimp (initial weight 0.52 ± 0.16 g) were reared in 33.3 L aquarium at a density of 3,000 shrimp/m³ for 21 days, with biofloc densities of 5, 10, and 15 mL/L, and challenged with V. parahaemolyticus (10³ CFU/mL). Controls included pathogen-exposed shrimp without biofloc (positive control) and pathogen-free shrimp with no biofloc (negative control). Bacterial inhibition and biofilm formation were assessed, growth performance was measured by final weight and specific growth rate (SGR), and immune responses were evaluated by total hemocyte count, phagocytic activity, respiratory burst, and phenoloxidase activity. While there was no significant difference in growth performance among the biofloc density treatments, the biofloc system overall showed higher growth performance compared to the control groups. However, the 15 mL/L biofloc density significantly reduced V. parahaemolyticus density and biofilm formation (p<0.05) and enhanced immune responses compared to the controls. In conclusion, biofloc supplemented with Bacillus sp. NP5 significantly improved shrimp health and productivity, with 15 mL/L biofloc density providing optimal pathogen reduction and immune enhancement, despite no significant growth performance differences among the treatments.