Gut microbiota changes in Hexagrammos otakii during development and association with diets based on metagenomics sequencing

The development of microbial communities is important for the growth of the fat greenling Hexagrammos otakii; however, the relationship between microbial communities and fish diet is poorly understood. Here, we used metagenomics sequencing to investigate the gut microbiota of H. otakii at three key time points during development. The gut microbial diversity and community composition of H. otakii presented stage-specific signatures and appeared to shift with different diets and environmental conditions such as NH4 + -NO2- etc. Metagenomics analysis indicated that the dominant phyla were Proteobacteria and Firmicutes. With dietary changes from rotifers and Artemia to formulated feed, the dominant genera shifted from Vibrio and Photobacterium to Lactococcus, and variations in the gut microbiota increased with age. Based on metagenomics functional annotation using the Kyoto Encyclopedia of Genes and Genomes database, growth and diet at different stages affected the metabolic function of the gut microbiome by activating carbohydrate and amino acid metabolism while weakening lipid and nucleotide metabolism. In addition, as predicted by the Carbohydrate-Active enZymes database, glycoside hydrolase and glycosyl transferases may be involved in food degradation. Our results suggest that the H. otakii gut microbiota assembly was coupled to animal development and host age-associated biotic features and changes. Diet had a considerable effect on these distinct communities at different times, indicating that the fish gut microbiota rapidly adapted to dietary shifts. The microbiota therefore likely plays an indispensable role in nutrient turnover and fermentation. These findings can provide guidance for the development of probiotics and the application of feed additives.