Abstract:The aim of this project was to investigate the characteristics of the microbiota structure and the activity of digestive and nonspecific immune enzymes in the gastrointestinal tract of large yellow croaker (Larimichthys crocea). We systematically analyzed the composition and distribution of microbiota in the stomach, pyloric caecum, and gut of large yellow croaker using high-throughput sequencing. Moreover, we conducted comparative analysis of the gastrointestinal tract microbiota in large yellow croakers cultured via the industrialized or net cage culture pattern. Under these two aquaculture patterns, we analyzed the activity of digestive and nonspecific immune enzymes in the gastrointestinal tract through biochemical methods. The microbiota diversity in the gastrointestinal tract declined under both aquaculture patterns. The genera including Lactobacillaceae(f), Fructobacillus and Flavobacterium, and etc, were the shared and dominant microbiota. The abundances of Bacteroides and Anaerostipes declined from the beginning of the gastrointestinal tract to the end, while those of Flavobacterium and genera represented by Lactobacillaceae (f) and the E01_9C_26_marine_group increased under both aquaculture patterns. Genera belonging to Prevotella_9 and Lactobacillaceae(f) were the main different species between these two aquaculture patterns. Under the industrialized pattern, the composition of microbiota and number of genes involved in metabolic pathways associated with nutrition and immunity were not significantly different between the pyloric caecum and gut (P>0.05), while these values obviously different from those in the stomach. In contrast, under net cage culture, differences between the stomach and pyloric caecum or gut decreased. The microbiota composition of the gastrointestinal tract of large yellow croakers cultured with these two patterns was similar to that of the feed. Additionally, the stomach and pyloric caecum exhibited nonspecific immune enzyme activities, indicating that the entire gastrointestinal tract functions as a chemical immune barrier. These results can serve as a basis for healthy large yellow croaker cultures and provide a theoretical foundation for studying the physiological functions of the gastrointestinal tract microbiota.
