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 x 10(6) CFU per g pellet) were administered in shrimp. The growth rate (2.36% day(-1) ), red-colour score (25) and astaxanthin concentration (3.5 microg 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.