Addition of Bdellovibrio to aquaculture water can significantly alter the distribution of microbial community on the gills and enhance the survival rate of Carassius auratus gibelio.

Bdellovibrio has shown promising potential as a "living antibiotic" in aquaculture due to its predatory nature towards bacteria. However, limited research has been conducted on the impact of Bdellovibrio on fish microbiota distribution and whether these effects are beneficial to the fish. This study aimed to investigate the effects of introducing Bdellovibrio into the aquaculture water of Carassius auratus for a two-month period, focusing on growth, survival rates, and gill microbiota distribution. The results revealed that the addition of Bdellovibrio significantly decreased the number of culturable bacteria in the water (P < 0.05) and improved the survival rates of C. auratus (P < 0.05). However, it had no significant impact on the fish's body weight gain rate (WGR) or specific growth rate (SGR). Microbiome 16S sequencing demonstrated a significant presence of Bdellovibrionota in the experimental group, which was absent in the control group. At the phyla level, Bdellovibrio had a notable influence on the distribution of microbial communities, particularly on Proteobacteria, Bacteroidota, Actinobacteriota, Verrucomicrobiota, and Deinococcota (P < 0.05). Additionally, the addition of Bdellovibrio reduced the abundance of Enterobacterales bacteria, as indicated by LEfSE analysis. The presence of Bdellovibrio in the gills of the experimental group was confirmed through PCR and qPCR detection. Furthermore, the Kaplan-Meier survival curves of C. auratus following immersion infections of Aeromonas hydrophila demonstrated effective protection when Bdellovibrio was added. In conclusion, these findings suggest that Bdellovibrio can serve as a substitute for antibiotics and positively influence microbial communities, ultimately benefiting the healthy growth of C. auratus. This study highlights the immense potential of Bdellovibrio as an antibiotic alternative in aquaculture. • The addition of Bdellovibrio to water significantly reduced the number of culturable bacteria in the water. • The Bdellovibrio could significantly increase the survival rates of crucian carps. • The Bdellovibrio can be obviously detected on foregut, midgut, hindgut and gills after long-term addition. • The Bdellovibrio can reduce the number of Enterobacterales bacteria. • The Bdellovibrio exhibit effectively protections of C. auratus after Aeromonas hydrophila immersion infections. [ABSTRACT FROM AUTHOR]