| Bile acid supplemented in diet of some fish species can play a variety of biological activities and have beneficial effects on growth and body health.The study of bile acid application in eel diet was rarely reported.This trial was conducted to investigate the effects of dietary bile acid supplementation on growth performance,serum biochemical parameters,intestinal flora and liver metabolism of juvenile European eel（Anguilla anguilla）.The fish cultured in 9 intensive ponds with water recirculating system,average body weight being 141.5±1.9 g per fish and average total weight being 681.7±22.7 in each pond,were randomly divided into three treatment groups with three replicates in each group.The bile acid levels of the three treatment groups were 0 mg/kg（control group）,500 mg/kg（BA1 group）and 1000 mg/kg（BA2 group）,respectively.The trial period was 105 days.The results were presented as follows:Compared with control group,the weight gain rate and specific growth rate of BA1 group and BA2 group were significantly increased（P<0.05）,the activities of protease and lipase in intestinal tract were improved significantly（P<0.05）.The levels of serum blood urea nitrogen,triglyceride,total cholesterol and low density lipoprotein cholesterol,the glutamic-oxalacetic transaminase and glutamic-pyruvic transaminase were significantly decreased（P<0.05）.The levels of immunoglobulin M and Complement 3,and the activities of alkaline phosphatase,acid phosphatase and lysozyme were significantly increased（P<0.05）.The activity of lysozyme in BA1 group was higher than that of BA2 group,while there was no significant difference of alkaline phosphatase activities between BA1 group and control group or BA2 group（P>0.05）.In the liver,the content of malondialdehyde was significantly decreased（P<0.05）.The level of total antioxidant capacity,the activities of total superoxide dismutase and the content of reduced glutathione were significantly increased in BA1 group and BA2 group（P<0.05）,there was no significant differences between BA2 group and control group or BA1 group（P>0.05）.The activities of lipoprotein lipase,hepatic lipase and total lipase were improved significantly（P>0.05）,while the levels of fatty acid synthetase and acetyl CoA carboxylase were significantly decreased,and the activities of acetyl CoA carboxylase were not significantly different between BA2 group and control group（P>0.05）.In the liver and muscle,the content of lipid was significantly decreased（P<0.05）,the content of protein was significantly increased in liver（P<0.05）.Except for lysozyme activity,all of the aboveparameters were not significantly different between BA1 group and BA2 group（P>0.05）.Compared with the control group,the number of total OTU and Chao1 index in bile acid groups were significantly increased（P<0.05）,and the Shannon index were decreased significantly.Those results indicated that bile acid could decrease the diversity of intestinal flora and increase the flora relative abundance.At the phylum level,the relative abundance of Spirochetes and Firmicutes were decreased in BA1 group and then increased in BA2 group.The relative abundance of Bacteroidetes and Proteobacteria were decreased,the relative abundance of Fusobacteria and Actinobacteria increased in BA1 group and decreased in BA2 group,while the relative abundance of Tenericutes gradually increased with the increasing bile aicd supplemented levels.At genus level,the relative abundance of Macellibacteroides,Edwardsiella,Clostridiumsensustricto13 and Plesiomonas in BA1 group were higher than those in control group or BA2 group（P<0.05）.Compared with the control group,the levels deoxycholic acid,glycodeoxycholic acid and glycodeoxyursodeoxycholic acid in liver were significantly increased in 500 mg BA /kg group（P<0.05）,but other bile acids were not significantly affected（P>0.05）.A total of 49 differential metabolites were found between bile acid group and control group,which mainly belonged to metabolites such as amino acids,fatty acids,organic acids and vitamins.There were 33 metabolites up-regulated and 16 metabolites down-regulated.The metabolic pathways enriched by different metabolites included tRNA biosynthesis,amino acid biosynthesis and sphingolipid metabolism,etc.Those metabolic pathways were mainly related to amino acid metabolism and lipid metabolism.In conclusion,the bile acid supplemented in diet of juvenile European eel could effectively improve the activities of intestinal digestive enzymes,serum immune ability and liver health status.The relative abundance and species diversity of intestinal flora were adjusted by bile acid supplementation.The levels of different bile acids in liver were increased to some extent.The activity of lipid catabolism enzymes in liver were increased with the decreasing levels of lipid synthases.It was found that bile acid could mainly regulate the intensity of amino acid metabolism and lipid metabolism in liver,reduce fat deposition in muscle and liver,increase protein synthesis.The bile acid could play the role in promoting growth through the above ways.There were similar effects of 500 mg/kg or 1000 mg/kg bile acid supplementation on growth and most physiological and biochemical parameters of juvenile European eel. |
