Dietary and water probiotics enhance immunity, modulate microbiota, and increase survival of Penaeus vannamei challenged with V. parahaemolyticus.

This study evaluated the effects of Bacillus licheniformis and Pediococcus pentosaceus administered in both culture water and feed to Penaeus vannamei over a 47-day experiment. Treatments in triplicate were as follows: (I) Commercial Feed (CF); (II) CF + P. pentosaceus in the water (3 × 10⁶ CFU/L); (III) CF + B. licheniformis in the water (3 × 10⁶ CFU/L); (IV) P. pentosaceus in fermented feed (51 × 10⁵ CFU/g); (V) B. licheniformis in fermented feed (147 × 10⁶ CFU/g); (VI) Mix of P. pentosaceus (140 × 10⁵ CFU/g) + B. licheniformis (180 × 10⁵ CFU/g) in fermented feed + Mix of P. pentosaceus + B. licheniformis (3 × 10⁶ CFU/L) in the water. Growth, immune effectors (phenoloxidase and superoxide anion), and gut bacterial profiles via 16S metagenomic sequencing were assessed. Survival was determined after a challenge with Vibrio parahaemolyticus. Probiotics did not affect growth. Only B. licheniformis in water and fermented feed elicited a significant immunostimulatory response, increasing superoxide anion production and phenoloxidase activity, respectively. Probiotic administration also modulated the gut microbiota, significantly increasing the relative abundance of beneficial genera like Ruegeria and Haloferula. Measures of both alpha and beta diversity indicated a significant restructuring of the microbial community in response to probiotics. Most major bacterial groups showed predominantly positive intra-group interactions, while Psychromonadaceae solely exhibited negative interactions with other families. Shrimp survival was significantly higher in shrimp treated with probiotics, excluding treatment II. These results demonstrate that probiotics strengthen innate immunity and improves disease resistance in shrimp by enhancing immunocompetence and enriching beneficial gut microbes, offering a viable strategy for sustainable aquaculture health management.