Bacillus velezensis AP193 exerts probiotic effects in channel catfish (Ictalurus punctatus) and reduces aquaculture pond eutrophication

Ictalurus punctatus (channel catfish) is an economically important farmed fish particularly in the southeastern United States. Aquaculture sustainability is threatened by disease pressure and the eutrophic conditions resulted from intensive fish farming. Previous research identified Bacillus velezensis strains that reduced mortality due to bacterial pathogens when used as a feed amendment. This study was conducted to determine the effects of B. velezensis-amended feed on catfish growth performance, pond water quality, and on the microbiomes in fish intestines and pond water. B. velezensis AP193 was evaluated in a ten-week pond trial, with four replicate ponds per probiotic treatment or control group. Feed amended with B. velezensis AP193 induced a 40.4% or 32.6% increase in growth relative to control feed in fingerling catfish that originated from aquaria or raceways, respectively. No significant differences were observed in the catfish intestinal microbiota or the pond microbiota due to probiotic-amended feed. The water quality was improved in ponds in which fish were fed with the probiotic-amended feed, as significant reductions were found in total phosphorus (19%), total nitrogen (43%) and nitrate (75%). These data suggest that B. velezensis AP193 can promote catfish growth and improve pond water quality when used as a feed amendment.