Aquaculture Reports (Nov 2021)
Probiotic effects of the Bacillus velezensis GY65 strain in the mandarin fish, Siniperca chuatsi
Abstract
Traditional culture of the mandarin fish (Siniperca chuatsi), an important freshwater fish in China, is restricted by live bait fish, as the difficulty of utilizing plant-derived nutrients in its artificial feed hinders its industrialization of artificial feed. This study evaluated the effect of the Bacillus velezensis GY65 strain, which shows probiotic effects on digestive and bacterial infections in mandarin fish. The complete genome of B. velezensis GY65 was obtained via sequencing. Seven amylase coding genes that could improve the fish digestion of plant feeds were identified. Twelve gene clusters of secondary metabolites related to antibacterial compounds were identified using the antiSMAH database. The effects of B. velezensis GY65 on growth performance, digestive enzyme capacity, antioxidant capacity, and innate immune response of mandarin fish were evaluated. The results showed a significantly (P < 0.05) increased weight gain rate, specific growth rate, viscera index, and condition factor in mandarin fish fed with B. velezensis GY65 compared with those fed with the basal diet. Amylase, protease, lysozyme, catalase, and superoxide dismutase activities were significantly (P < 0.05) enhanced in the B. velezensis GY65-supplemented groups. Relative expressions of HSP70, TNF-α, and IL-8 gene were significantly (P < 0.05) advanced in mandarin fish fed with B. velezensis GY65 in comparison with the basal group. Cumulative mortality was significantly decreased in fish fed with B. velezensis GY65 after Aeromonas hydrophila GYK1 infection. We conclude that B. velezensis GY65 enhanced amylase activity, improved growth performance, strengthened non-specific immunity, and reduced the risk of pathogenic infection of mandarin fish, which further suggest that B. velezensis GY65 can be used as an additive in artificial feed of mandarin fish.
