Comparative analysis of gut microbiota and intestinal transcriptomic profile between fast- and slow-growing American eels (Anguilla rostrata)

During American eel farming (from glass eels to silver eels), significant individual growth differences were commonly observed even under the same farming conditions. However, the underlying mechanism is not clear. In this study, a batch of glass eels (∼ 0.05 g/ind.) was cultured under the same conditions for 8 months. After farming, the gut microbiota and intestinal transcriptomic profile of the slow-growing eels (SGE, with a body weight 200 g) were compared. An obvious difference in gut microbiota was observed between FGE and SGE, indicating that the gut microbiota might play a role in influencing growth performance. The relative abundance of Firmicutes, a short chain fatty acids (SCFAs)-producing phylum, in FGE was higher than SGE, suggesting that the gut microbiota in FGE could make a better use of the non-digestible polysaccharides in the diet and produce more SCFAs for the host. The intestinal transcriptomic analysis revealed 1139 genes highly positively associated with growth performance. These genes were enriched in the Lipid metabolism pathway, suggesting that the lipid metabolism activity (e.g., utilizing SCFAs to synthesize lipid or glucose) was increased in FGE. Taken together, we speculated that with the cooperation of gut microbiota and intestine tissues, FGE might make a better use of the non-digestible polysaccharides in the diet and obtain an extra source of energy, resulting in a higher growth rate. This study deepens our understanding of the role of gut microbiota in affecting fish growth, and the indicative taxa identified in FGE (such as Faecalibacterium) could provide a valuable reference for the eel probiotics development.