Comparison of growth, digestive enzyme activity, immune response and intestinal microbiota in large yellow croaker ( Larimichthys crocea ) with different sizes

Fish from the same batch often appeared different growth rates. However, there was little knowledge on the differences in the digestive enzyme activity, immune response and intestinal microbiota of fish with different sizes from the same parents. In the present study, we chose large yellow croaker to characterize the differences in digestive enzyme activity, immune response between the larger-sized and smaller-sized individuals, meanwhile, a comprehensive comparison of the composition, structure, community assembly, interactions between species and metabolites of intestinal microbiota were executed. Results revealed that the daily growth coefficient of the larger-sized large yellow croaker was significantly higher than that in the smaller-sized individual. The activities of protease, amylase, alkaline phosphatase, acid phosphatase and lysozyme in the larger-sized individual were significantly higher than those in the smaller-sized individual. The expression levels of TLR-related genes in the intestine and liver of the larger-sized individual were all significantly higher than those of the smaller-sized individual, meanwhile the expression levels of pro-inflammatory cytokines (IL beta and IL6) in the larger-sized individual were significantly lower than those in the smaller-sized individual. The Shannon and Simpson indices of intestinal microbiota in the larger-sized individuals increased significantly. The composition of intestinal microbiota was similar in the smaller-sized and larger-sized individuals. Stochastic processes dominated the intestinal community assembly in the large yellow croaker no matter at smaller-sized or larger-sized. The network of intestinal microbiota in the larger-sized individual was more stable and effective. Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi Firmicutes and Proteobacteria were the core species in the large yellow croaker no matter at smaller-sized or larger-sized. Metabolites belonging to amino acids, bile acids and short chain fatty acids were abundant in larger-sized individuals. The results of this study would help us to know the growth differences for fish.