oint effects of gut microbiota and its metabolites on growth of carp in rice-fish coculture system

Gut microbiota and their metabolites play a crucial role in regulating the health and growth of the host. However, the mechanism how the gut microbiome affects the growth rate of fish (Cyprinus carpio) in the rice-fish coculture system remains unclear. In this study, the gut contents of the fast-growing and slow-growing (FG and SG) carp from the rice-fish coculture system were collected for both the gut microbiome and metabolome analysis. High throughput 16S rRNA gene sequencing showed that the gut microbiota of FG group was significantly different from that of SG group. In particular, compared with FG group, the cyanobacteria of SG group was highly enriched (18.61% vs<0.20%). The liquid chromatography-mass spectrometry (LC-MS) analysis revealed that there were 191 named differential metabolites and 18 enriched KEGG pathways between the two groups, of which more than 50% of these metabolites were involved in lipid and amino acids metabolism. Compared with the FG group, the SG group significantly increased the metabolic pathways involved in the steroid (hormone) biosynthesis, but decreased those of beta-alanine metabolism, biosynthesis of unsaturated fatty acids and bile secretion, leading to the enrichment of steroid metabolites and the reduction of spermidine concentration, which may affect the growth rate of carp. The metabolome results were further supported by the predicated KEGG functions of the gut microbiomes of the two groups, indicating the gut microbiota could substantially affect the growth of fish via their unique metabolic functions, which provides inspiration to the development of microbiome technologies in aquaculture.