Chronic ammonia stress caused disorder of intestinal microbiota and damaged intestinal structure and function in yellow catfish (Pelteobagrus fulvidraco)

Ammonia is one of the major chemicals in aquatic environmental systems, and high concentrations of ammonia are toxic to fish. Also, ammonia stress can damage the intestine of fish. We wanted to know how chronic ammonia stress affects the intestinal microbiota and function of yellow catfish (Pelteobagrus fulvidraco). In this study, chronic ammonia stress (control group, 0.5 and 2.5 mg/L ammonia stress groups, continued 28 d) on intestinal structure, function and microbiota of the yellow catfish were explored. Chronic ammonia stress induced changes in the intestine microbiota according to 16 S high-throughput sequencing. The ACE, Shonnon and Chao indices of intestine microbiota showed an increasing trend in the 2.5 mg/L ammonia-stressed group. Ammonia stress also led to changes in the intestinal microbiota and the relative abundance of bacteria. We found the abundance of Flavobacteriaceae, Vibrio, Pseudomonas, Aeromonas and Streptococcus showed increasing tendency in ammonia stress groups. The H&E staining showed that chronic ammonia stress caused in marked epithelial cell necrosis and lamina propria edema and reduced width of intestinal villi significantly. We also found chronic ammonia stress significantly decreased in the number of goblet cells by PAS staining. In addition, ammonia stress caused significant decrease in activities of pepsin, chymotrypsin and trypsin. In summary, ammonia stress led to disruption of intestinal microbiota, causing damage of the intestinal structure and affecting the normal physiological function of the intestine.