Analysis of bile acid composition in Megalobrama amblycephala tissues and effects of high-carbohydrate diet feeding

Carbohydrate is an important non-protein energy source in aquaculture. Adding proper amount of carbohydrate to feed can not only reduce the decomposition energy supply of protein and improve its utilization rate, but also reduce the ammonia nitrogen emission of aquatic animals, thus reducing the pollution of aquaculture water. However, excessive addition of carbohydrate can inhibit fish growth, lead to occurrence of hepatobiliary diseases and the decline of stress resistance, and ultimately reduce the benefits of aquaculture. Related studies have shown that the addition of bile acids to feeds can regulate the glycolipid metabolism of fish and alleviate the metabolic disorders caused by high carbohydrate, but the effects of long-term feeding of high-carbohydrate feeds on the bile acid composition of fish and its in-depth analysis have not yet been reported. The purpose of this experiment is to analyze the bile acid spectrum of Megalobrama amblycephala, and evaluate its changes after a long-term feeding of a high-carbohydrate diet. The results can partly unveil the mechanisms underlying the hepatobiliary syndromes of fish, and provide scientific guidance for the corresponding nutritional interventions. A total of two experimental diets were prepared, including a control diet (29% nitrogen-free extract) and a high-carbohydrate diet (HC, 41% nitrogen-free extract). Each diet was fed to four replicates of juvenile M. amblycephala (35.20 ± 0.15) g for 12 weeks. Then, the bile acid spectrum of M. amblycephala was analyzed in the liver, gallbladder, hindgut and plasma using the high-throughput target quantitative detection technology. The results showed that both taurochenodeoxycholic acid (TCDCA) and taurocholic acid (TCA) are the main bile acids in M. amblycephala, and there was a significant positive correlation between them. Compared with the control group, the contents of taurolithocholic acid-3-sulfate (TLCA-3S) increased significantly in the liver of the HC group. The contents of chenodeoxycholic acid (CDCA), taurolithocholic acid-3-sulfate (LCA-3S), glycocholic acid (GCA), TCDCA, TCA, chenodeoxycholic acid (ACA) and taurodeoxycholic acid (TDCA) all decreased significantly in the liver of the HC group. The contents of TCDCA and TCA both increased significantly in the gallbladder of the HC group, while that of LCA-3S and lithocholic acid (LCA) both decreased significantly. The levels of LCA increased significantly in the hindgut of the HC group, while that of cholic acid (CA)、LCA-3S、GCA、TCDCA、TCA and glycodeoxycholic acid (GDCA) all decreased significantly. Furthermore, the contents of cholic acid (CA)、LCA and TLCA-3S all increased significantly, while that of chenodeoxycholic acid 24-acyl-β-D-glucuronide (CDCA-24Gln) decreased significantly. In addiiton, glycine-conjugated bile acids were found in the tissues of M. amblycephala, including GCA, glycochenodeoxycholic acid (GCDCA) and glycoursodeoxycholic acid (GUDCA). Furthermore, tauro-α-muricholic acid (T-α-MCA) was first found in fish. In conclusion, both TCDCA and TCA are the main bile acids in M. amblycephala, and there was a significant positive correlation between them. A long-term feeding of the HC diet significantly decreased the total bile acid content, and altered the component of bile acids.