| Fish oil is often used as a feed additive in the process of aquaculture due to its rich nutritional value.But it is precisely because it is rich in polyunsaturated fatty acids,fish oil is easy to oxidize and deteriorate under the action of irresistible factors such as production,transportation,and the surrounding environment.The primary and secondary metabolites such as aldehydes,ketones,alcohols,esters and acids produced by oxidized fish oil directly affect the absorption and metabolism of feed nutrients by aquatic animals,threaten the health of fish,and then have an unpredictable impact on the income of farmers.At present,the research direction of oxidized fish oil is mostly focused on the negative effects of oxidative stress on aquatic animals,but there arefew studies on the effects of exogenous addition of oxidized fish oil on lipid metabolism in aquatic animals.In addition,in recent years,L-carnitine plays a very important physiological regulating role in the process of lipid metabolism.In order to achieve the purpose of saving protein,L-carnitine is often used as an additive in aquaculture feed,so it has attracted the attention of researchers at home and abroad.However,the effect of L-carnitine on lipid metabolism in aquatic animals ingested oxidized fish oil has not been reported.Therefore,in this experiment,the locally famous and special species of fish-Rhynchocypris lagowski Dybowski was taken as the research object,and the oxidized fish oil,which was harmful to fish health,was taken as the premise to study the regulatory effect of exogenous intake of L-carnitine on lipid metabolism in the body tissue of Rhynchocypris lagowski Dybowski.The purpose of this study is to provide a reference for elucidating the mechanism of lipid metabolism of L-carnitine and its application in practical production.This study consists of four parts.The results and conclusions are as follows:(1)Effects of oxidized fish oil on the fatty acid composition of muscle and hepatopancreas of Rhynchocypris lagowski Dybowski.In order to study the effect of oxidized fish oil on the fatty acid composition of muscle and hepatopancreas of Rhynchocypris lagowski Dybowski,fresh fish oil was used as a control group.Fresh fish oil was oxidized to four degrees(Peroxide value POV:100 meq/kg,200 meq/kg,300 meq/kg,and 400 meq/kg)by artificial oxidation in 55?water bath pot.Five groups of the same energy feed were made from fresh fish oil,oxidized fish oil with POV value of 100,200,300,and 400 meq/kg as a fat source.A total of 525 healthy Rhynchocypris lagowski Dybowski(4.48 ± 0.14 g)were randomly assigned to 15 buckets and randomly divided into 5 groups with 3 repeats in each group and 35 fish in each group.Five groups of healthy Rhynchocypris lagowski Dybowski were randomly divided into 5 groups and fed with 5 groups of feed respectively.After 8 weeks of culture,the muscle and hepatopancreas were taken to determine the composition of fatty acids.The results show that oxidized fish oil had a significant effect on the fatty acid composition of muscle and hepatopancreas(P <0.05).The content of PUFA fatty acids in the muscle of Rhynchocypris lagowski Dybowski increased significantly,and it was positively correlated with the oxidation degree of fish oil added to the feed,but the contents of SFA,MUFA,EPA,and ?n-6fatty acids did not change significantly(P > 0.05).Compared with the control group,the contents of SFA,MUFA,and EPA fatty acids in hepatopancreas increasedsignificantly,but the contents of DHA,? n-3,? n-6,and PUFA fatty acids decreased.The results showed that the exogenous addition of oxidized fish oil significantly affected the fatty acid composition of muscle and hepatopancreas of Rhynchocypris lagowski Dybowski,and significantly decreased the contents of PUFA in muscle and SFA and MUFA in hepatopancreas,indicating that the intake of oxidized fish oil may lead to changes in the utilization and metabolism of fatty acids.(2)Effects of oxidized fish oil on lipid metabolism enzyme activity and gene expression in the hepatopancreas of Rhynchocypris lagowski Dybowski.Hepatopancreas samples were taken to determine the activities of enzymes related to lipid metabolism and gene expression.To study the effects of oxidized fish oil on lipid metabolism enzyme activity and gene expression in the hepatopancreas of Rhynchocypris lagowski Dybowski.The results showed that the contents of triglyceride,cholesterol,and HDL/LDL ratio in hepatopancreas increased significantly with the increase of oxidation degree of fish oil in the feed(P < 0.05).Further analysis of the enzyme activity and gene expression related to lipid metabolism showed that the content and gene expression of enzymes closely related to lipid metabolism,such as FAS,ACC?,and gene expression,were significantly increased(P < 0.05),while the contents of HL,ACS,CPT-1,and HSL? related enzymes related to lipid metabolism and transport were significantly decreased(P <0.05).Studies have shown that the diet of oxidized fish oil may promote fatty acid synthesis,inhibit fatty acid oxidation,increase fatty acid uptake by hepatopancreas,and reduce the ability of TG transport from hepatopancreas to extrahepatic tissues,thus inducing fat accumulation in hepatopancreatic cells and further affecting lipid metabolism in hepatopancreas.(3)Effects of L-carnitine on the fatty acid composition of muscle and hepatopancreas in oxidized fish oil feed of Rhynchocypris lagowski Dybowski.In order to explore the effect of exogenous addition of L-carnitine on lipid metabolism of oxidized fish oil fed with oxidized fish oil-feed,select healthy Rhynchocypris lagowski Dybowski 735(4.48 ± 0.14 g)assigned to 21 buckets,divided into 7 groups,each group has 3 repeats,each repeat 35.Based on the experimental results of chapter 1 and chapter 2,oxidized fish oil with POV 100meq/kg and POV 400 meq/kg was selected and fed with oxidized fish oil.Two different concentrations of L-carnitine(500 mg/kg and 1000 mg/kg)were added to the two kinds of oxidized fish oil feed,and fresh fish oil was used as the control group.7experimental groups were set up.The muscle and hepatopancreas of Rhynchocypris lagowski Dybowski were fed for 8 weeks,and the fatty acid composition of the muscle and hepatopancreas was determined.The results showed that except for the contents of SFA and MUFA fatty acids(P > 0.05),the contents of EPA,DHA,and PUFA fatty acids in the muscle of Rhynchocypris lagowski Dybowski were significantly higher than those in the control group(P < 0.05),and reached the maximum in the OFO 100+LC 500 group.The fatty acid contents of SFA,MUFA,?n-6 and PUFA in hepatopancreas were significantly increased(P < 0.05),The content of SFA reached the maximum in OFO 100+LC 500 group.The results showed that compared with POV 100meq/kg oxidized fish oil group,the addition of different doses of L-carnitine significantly increased the content of PUFA fatty acids in muscle and SFA fatty acids in hepatopancreas,indicating that the addition of L-carnitine may change the ability of fatty acid utilization and metabolism in muscle and hepatopancreas of Rhynchocypris lagowski Dybowski under the condition of oxidized fish oil.(4)Effects of L-carnitine added to oxidized fish oil feed on lipid metabolism enzyme activity and gene expression in the hepatopancreas of Rhynchocypris lagowski Dybowski.Hepatopancreas samples were taken to determine the activities of enzymes related to lipid metabolism and gene expression.The results showed that the addition of L-carnitine significantly decreased the contents of triglyceride,cholesterol,and HDL/LDL ratio in hepatopancreas(P < 0.05).The results of lipid metabolism-related enzyme activity and gene expression showed that the content and gene expression of FAS and ACC? related to lipid metabolism synthesis decreased with the addition of L-carnitine,while the contents of HL,ACS,CPT-1 and HSL ? related to lipid metabolism and transport increased significantly(P < 0.05).The results showed that under the experimental conditions,the addition of L-carnitine promoted the oxidation of fatty acids in hepatopancreas,indicating that L-carnitine may improve the fat accumulation in hepatopancreatic cells induced by oxidized fish oil.All the results showed that:(1)The intake of oxidized fish oil accelerated the decomposition of PUFA fatty acids in muscle and SFA in hepatopancreas,and changed the utilization and metabolism of fatty acids in muscle and hepatopancreas of Rhynchocypris lagowski Dybowski.(2)The effect of oxidized fish oil intake on the activity of lipid metabolic enzymes was studied.The results showed that an oxidized fish oil diet could promote the synthesis of fatty acids,increase the uptake of fatty acids by hepatopancreas,reduce the ability of TG transport from hepatopancreas to extrahepatic tissues,and induce fat accumulation in hepatopancreatic cells.(3)The exogenous addition of L-carnitine significantly increased the content of PUFA fatty acids in muscle and SFA fatty acids in hepatopancreas,indicating that the addition of L-carnitine may change the utilization and metabolism of fatty acids in muscle and hepatopancreas under the condition of oxidized fish oil.(4)The results of lipid metabolism and related gene expression in hepatopancreas showed that L-carnitine promoted fatty acid decomposition in oxidized fish oil,and fatty acid uptake by hepatopancreas decreased.It may have the effect of improving lipid accumulation in hepatopancreatic cells induced by oxidized fish oil. |
PDF Full Text Request