Cooperative improvement in growth rate, red‐colour score and astaxanthin level of white‐leg shrimp by Bacillus strains originating from shrimp gut

Aims We investigated the potential cooperative effects of carotenoid‐producing Bacillus aquimaris SH6 and nonpigmented Bacillus subtilis SH23 on white‐leg shrimp growth and health. Methods and Results SH6, SH23 and a combination of both spores (1 × 106 CFU per g pellet) were administered in shrimp. The growth rate (2·36% day−1), red‐colour score (25) and astaxanthin concentration (3·5 µg g−1 shrimp) were maximum in two‐spore‐administered shrimp. Immune‐related Rho mRNA expression level and phenoloxidase and superoxidase dismutase activities were higher in two‐spore‐administered shrimp than in control shrimp, with Rho mRNA expression level being 55‐fold higher in two‐spore‐administered shrimp than in SH6‐administered shrimp and phenoloxidase activity being 1·2‐fold higher in two‐spore‐administered shrimp than in SH23‐administered shrimp. Although live SH6 count was 2·7‐fold lower, SH6 germination level was 3·5‐fold higher in the combination group than in SH6 group. Conclusions When both SH6 and SH23 spores were administered, SH6 spore germination was enhanced and cooperative improvement was seen in growth, astaxanthin level and red‐colour score of white‐leg shrimp; however, immune‐related parameters were induced in a noncooperative manner. Significance and Impact of the Study This is the first report showing the cooperative probiotic activities of Bacillus strains and their possible mechanisms in a shrimp model.