Effects of biological flocculation technology (BFT) on water quality dynamics and immune response of grass carp (Ctenopharyngodon idella)

The biofloc technology (BFT) offers benefits in improving feed utilization and reducing the feed conversion ratio compared to the recirculating aquaculture system (RAS). In this study, high-throughput 16S rRNA gene sequencing was employed to investigate and compare the bacterial communities in these aquaculture systems and the gut microbiota of grass carp reared in them. We observed a significant distinction between the microbial communities of the aquaculture systems and the intestinal microbiota of grass carp. The genera cetobacterium and bacillus were more abundant in the BFT system, accounting for only 0.05% and 0.25% in the RAS. Our study also demonstrated that BFT could influence the intestinal microorganisms of grass carp (Ctenopharyngodon Idella) by reducing the relative abundance of burkholderia-caballeronia-paraburkholderia and increasing that of cetobacterium. Based on bugBase community predictions, the potential pathogenicity in BFT and grass carp intestine was lower than in RAS. Regarding gene expression in the grass carp intestine, immunosuppressive genes showed higher expression, while pro-inflammatory genes exhibited lower expression in grass carp reared in BFT. Furthermore, the final average length and weight of grass carp in the BFT system were significantly higher than those in the RAS. This study provides valuable insights into gut microbiome ecology in relation to two grass carp aquaculture systems, which could be effectively applied in grass carp management to promote health and improve water quality.