Pacific white shrimp (Litopenaeus vannamei) aquaculture is rapidly expanding, but disease-related losses constitute a sizeable economic impact on production. In particular, Vibrio parahaemolyticus, the bacterial agent of acute hepatopancreatic necrosis disease (AHPND), is of great concern for producers. Probiotics are increasingly used as a management tool in biofloc systems to improve water quality, growth, and enhance shrimp health.
A 56-day feeding trial was conducted in indoor biofloc tanks to evaluate two dose responses (PROX1 and PROX2) of a commercial Bacillus spp.-based probiotic (Pro4000X). At the trial endpoint, the probiotic application did not affect growth performance, including final biomass, mean weight, survival, and feed conversion ratio. However, probiotic treatments reduced mortality following an immersion challenge with V. parahaemolyticus (P < 0.001; Figure 1). This showed that the Bacillus probiotics used in this trial have improved the resistance in the probiotic-treated group.
Moreover, water quality, including ammonia, was lowest in the probiotic-treated group and significantly reduced settleable solids, while other water quality parameters were maintained in the acceptable ranges. Gene expression analysis revealed that the sod (superoxide dismutase) was significantly downregulated in the PROX1 group, suggesting reduced oxidative stress and more efficient immune regulation under probiotic supplementation. 16s sequencing revealed that the probiotics group showed higher microbial evenness and Shannon diversity and was enriched with beneficial taxa such as Ruegerias spp. and Rheinheimera spp. These taxa are associated with antimicrobial activity and nutrient cycling, supporting gut stability under pathogen exposure. These results showed that, regardless of dose, the probiotic enhanced disease resistance in shrimp, contributed to favorable modulation of immune gene expression, and reduced organic load in the biofloc system, thereby maintaining healthier culture conditions.