Biofloc system with synbiotic supplementation improves Penaeus vannamei immunity against AHPND

Mass mortality due to disease emergence has resulted in enormous losses in shrimp production. One of the deadliest shrimp pathogens is the disease-causing Vibrio parahaemolyticus (VP_AHPND), which induces acute hepatopancreatic necrosis and has recently become resistant to various classes of antibiotics. Biofloc systems and synbiotic feed supplementation are potential alternative strategies for overcoming this problem. In this study, a biofloc system was generated by inoculating the probiotic Halomonas alkaliphila, a consortium of nitrifying bacteria, and the microalgae Chaetoceros calcitrans with molasses at a C/N ratio of 15. The synbiotic-supplemented feed contained 0.375% (w/w) of prebiotic red seaweed Kappaphycus alvarezii powder, 0.125% (w/w) Spirulina sp., and freeze-dried H. alkaliphila powder at 10⁹ CFU/kg feed. Over a 84-day culture period, the biofloc system with or without synbiotic supplementation resulted in more stable water quality and significantly increased shrimp total biomass and survival. After a V. parahaemolyticus challenge, the highest survival was found in the biofloc system with or without a synbiotic (70 ± 0%), similar to the semibatch system supplemented with antibiotic enrofloxacin orally at 60 mg/kg body weight after pathogen injection (73 ± 6%). Gene expression analysis revealed enhanced humoral immune responses, with upregulation of antimicrobial peptides (ALF-a, lyz) and melanization (proPO). These findings suggest that the application of a biofloc system with or without synbiotic feed supplementation could be a potential alternative to antibiotics, increasing disease resistance and modulating the immune response against potential AHPND-causing V. parahaemolyticus infection in P. vannamei growout culture. KEY POINTS: • Bioflocs and synbiotics provide additional nutrients, promoting shrimp productivity • Bioflocs, with or without synbiotics, improve shrimp survival and humoral immunity • Bioflocs, with or without synbiotics, offer similar survival compared to enrofloxacin.