Abstract Objective This study evaluated the effect of commercial Bacillus spp. probiotics on growth performance, immunity, gut microbiota composition, and disease resistance to Vibrio parahaemolyticus in Pacific white shrimp Litopenaeus vannamei that were reared under biofloc conditions. Methods A 56-d feeding trial was conducted in a static biofloc system with postlarval shrimp (1.00 ± 0.03 g). A total of 1,080 shrimp were randomly assigned to three groups: two treatment levels (recommended dose PRO × 1 and a doubled dose PRO × 2) of a commercial probiotic blend, PRO4000X, alongside a control group (CTL; no probiotics). At the trial end point, hepatopancreas and gut samples were collected for gene expression. Gut samples were also obtained for gut microbiota analysis via 16S ribosomal RNA sequencing, and hemolymph samples were withdrawn to measure the total hemocyte count. Results Probiotic applications did not significantly affect growth performance, including final biomass, mean weight, survival, and feed conversion ratio under the experimental conditions. The probiotic-treated shrimp exhibited enhanced survival during a V. parahaemolyticus (strain A3) challenge, with significantly lower mortality rates (P 0.001; 42.5 ± 4.3% for PRO × 1 and 60 ± 6.5% for PRO × 2) relative to the CTL (100 ± 0.00%). Immune parameters, such as total hemocyte count, did not differ. Interestingly, the expression of the antioxidant gene sod (superoxide dismutase) in the shrimp gut was significantly downregulated in the PRO × 1 group relative to the control (P = 0.030), which suggests reduced oxidative stress under probiotic supplementation. The analysis of the gut microbiota revealed differences in alpha diversity, specifically in evenness and Shannon index, which were significantly higher in the PRO × 1 group. The analysis of the bacterial composition also revealed minor shifts in the dominant genera. Notably, Lysobacter was more abundant in the PRO × 1 group, which potentially reflects positive modulation of gut microbial communities in response to probiotic supplementation. Conclusions Overall, the application of PRO4000X probiotics significantly reduced the V. parahaemolyticus infection in the shrimp that were reared in biofloc water and supported the regulation of immunity and microbial communities in the gut. These findings indicate that probiotics potentially help to improve shrimp health when shrimp are cultured in biofloc systems.
Appuhami et al. (Tue,) studied this question.