Dietary β-conglycinin induces intestinal enteritis and affects glycerophospholipid and arginine metabolism in mirror carp (Cyprinus carpio)

The use of soybean meal in aquafeed industry is partially limited by anti-nutritional factors such as beta-conglycinin (beta-CG). However, the effects of beta-CG on mirror carp (Cyprinus carpio) growth performance and intestinal health has not been elucidated. This study investigated the effects of beta-CG levels on growth performance, intestine immunity, and intestinal lipid and protein metabolism in mirror carp. Four hundred and fifty mirror carp (4.22 +/- 0.03) g were fed a control (CON) diet containing fish meal as the protein source and four experimental diets containing beta-CG at 40 (beta-CG1), 80 (beta-CG2), 120 (beta-CG3), and 160 g/kg (beta-CG4) replacing the fishmeal, respectively. Each treatment had 30 fish replicated three times and the feeding was done for six weeks. The results showed that weight gain, specific growth rate, survival rate, protein efficiency, feed conversion ratio, and condition factor were not affected by dietary beta-CG (P > 0.05). Interestingly, the fish fed on the beta-CG diets upregulated significantly the expression of tumor necrosis factor alpha (TNF-alpha), interleukin-1 beta (IL-1 beta) and eIF4E-binding protein (4E-BP) in the proximal intestine (PI) than those fed on the CON diet (P < 0.05). The fish fed on the beta-CG2 diet decreased significantly the expression of transforming growth factor beta 1 (TGF beta 1) in the PI compared to those fed on the CON diet. The fish fed on the beta-CG diets downregulated significantly the expression of target of rapamycin (TOR) in the PI than those fed on the CON diet. The fish fed on beta-CG diets downregulated significantly the expression of AMP-activated protein kinase alpha (AMPK), acetyl-CoA carbox-ylase (ACC), TOR in the mid intestine (MI) while, claudin11 gene was significantly increased (P < 0.05). In the distal intestine (DI), feeding the fish on the beta-CG diets downregulated significantly the expression of AMPK and ACC genes, while increased the expression TNF-alpha, IL-1 beta and claudin11 (P < 0.05). Feeding the fish with the beta-CG diets mostly altered glycerophospholipid metabolism and arginine biosynthesis in intestinal mucosa. These re-sults suggest that dietary beta-CG induces enteritis in different intestinal segments and changes glycerophospholipid metabolism and arginine biosynthesis pathways. Fish farmers using soybean meal in the diets should process the ingredients to reduce beta-CG concentration before use.