GREEN LIVER SYMPTOM AND LIVER FIBROSIS CAUSED BY PECTIN OVERLOAD IN PELTEOBAGRUS FULVIDRACO MAY BE RELATED TO THE INTESTINAL DYSBACTERIOSIS

The content of dietary fibers in commonly used plant feedstuffs is often more than 30%, which is the fermentation substrate for intestinal flora. With the extensive use of low fish meal feed, cultured fish species are in a state of high dietary fiber loading. However, the nutritional stress induced by dietary fiber as well as the mechanism has not received enough attention. In the previous study, we found that high viscous dietary fiber pectin induced green liver symptom and liver fibrosis in yellow catfish, Pelteobagrus fulvidraco. The purpose of this study was to explore the role of intestinal flora in the above pathological process. The diets containing 30% dextrin and pectin were named CON and PEC diets respectively. Metronidazole was then added to CON and PEC diets in a dosage of 0.2% and the obtained diets were named CONM and PECM. The four diets were fed yellow catfish with an initial weight of (21.5±3.6) g, and sampling was conducted at 7d and 56d respectively. 16s rRNA analysis showed that metronidazole inhibited bacteria of Fusobacteria and Firmicutes, resulted in Proteobacteria became the first dominant bacteria. After 7 days of feeding, the green liver rate of fish fed diet CON, CONM, PEC, PECM was 0, 12%, 27% and 88% respectively. The green liver rate of all groups was low after 56d. The degree of liver fibrosis after 56d was the highest in fish fed diet PECM, followed by PEC, and the lightest in CON. Metronidazole significantly reduced the activity of bile salt hydrolase in digesta. The serum TBA concentration in fish fed diet PEC was significantly higher than those in CON, while that in fish fed diet CONM and PECM was significantly lower than those in CON. At 56d, the serum TBA concentration in fish fed diet CONM, PEC and PECM was significantly higher than that fed CON diet. The gene expression activity involved in bile acid synthesis, transport and regulation in liver was inconsistent with the green liver rate and the serum bile acid concentration. These results indicated that dysbacteriosis was an important cause of green liver symptom and liver fibrosis induced by pectin, which might be mediated by bile acid. In view of the extensive physiological effects of intestinal flora as well as bile acids, attention should be paid to the effect of dietary fiber in aquatic feed preparation.