| In this study,the mechanism of several kinds of oil was preliminarily discussed,and the optimal demand of feed lipid for Monopterus albus was determined,so as to provide scientific basis for the development of green and environment-friendly compound feed for eels and promote the healthy and sustainable development of eels breeding industry.The main results are as follows:1.Effects of different lipid sources on growth,biochemical indexes and apparent digestibility of Monopterus albusIn order to explore the effects of different lipid sources on the growth,physiological and biochemical indices and apparent digestibility of Monopterus albus,5% fish oil,soybean oil,linseed oil,palm oil and lard were added to the basic diet to prepare five kinds of isoenergetic test feeds for 10 weeks,which were fed to Monopterus albus(22.53±0.04g).the results:(1)The weight gain and specific growth rate of fish oil group and soybean oil group were significantly higher than those of linseed oil,palm oil and lard group(P<0.05),and the feed coefficient was significantly lower than those of the three groups(P<0.05).(2)The activities of glutamic oxaloacetic transaminase(GOT)and glutamic alanine transaminase(GPT)in serum of lard group were significantly higher than those of the other four groups(P<0.05);the contents of triglyceride,total cholesterol and free fatty acid in serum of fish oil group and linseed oil group were the lowest;the contents of high density lipoprotein(HDL-C)in serum of lard group were significantly lower than those of the other four groups,and there was no significant difference among the other four groups(P>0.05).(3)The activities of superoxide dismutase(SOD)and catalase(CAT)in fish oil,soybean oil and linseed oil groups were significantly higher than those in other groups(P<0.05);the content of malondialdehyde(MDA)was the highest in lard group and lysozyme(LZM)was the lowest,which was significantly different from the other four groups(P<0.05).(4)There was no significant difference in the apparent digestibility of crude protein and dry matter among the experimental groups.The apparent digestibility of crude lipid in fish oil group was the highest,while that in lard group was the lowest.The intestinal lipase activity in fish oil,soybean oil and linseed oil group was the highest,and the protease activity had no significant difference.(5)The crude lipid content of whole fish and liver in lard group was significantly higher than that of the other four groups(P<0.05),and there was no significant difference among the four groups(P>0.05);the crude lipid content of intestine,muscle and skin in each experimental group had no significant difference(P>0.05).(6)The liver structure of Monopterus albus was normal in fish oil,soybean oil,linseed oil and palm oil groups,and the liver cells in lard group were enlarged and swollen,resulting in liver injury such as cell rupture.The results showed that amongthe five lipid sources,fish oil and soybean oil group had the best growth,normal liver function,complete liver structure,active lipid metabolism,strong antioxidant capacity,which could improve the activity of amylase and lipase,and was not easy to form liver lipid deposit,which could obtain better economic and ecological benefits,followed by linseed oil and palm oil,while lard group was not physiological.It is suggested that some soybean oil should be added to replace fish oil in the preparation of eel feed.2.Effect of feed lipid level on growth and lipid metabolism of eelIn order to discuss the suitable lipid demand of eels,840 eels were randomly divided into 7 groups,with 4 replicates in each group and 30 in each.Fish oil and soybean oil(1:4)were mixed proportionally and added to the basic diet according to the proportion gradient of 0%,2%,4%,6%,8%,10%,12%.Seven kinds of isonitrogen feeds with different lipid levels were prepared.The numbers were L1,L2,L3,L4,L5,L6 and L7 in turn,which were fed to Monopterus albus(16.80±0.04g)10 weeks.The results showed that:(1)with the increase of feed lipid level,the weight gain multiple and specific growth rate first increased,then decreased,and the feed coefficient showed an opposite trend.Linear regression analysis showed that the optimum lipid level of eel was 7.03%~7.68%,low or high lipid content in feed was not conducive to eel growth.(2)The activity of GOT and GPT in serum of L6 and L7 groups was the highest.The serum concentrations of triglycerides,total cholesterol and free fatty acids increased with the increase of feed lipid level.The content of high-density lipoprotein in L3 and L4 groups was significantly higher than that in other groups(P<0.05),indicating that the appropriate level of lipid in the feed could make the body’s lipid metabolism more active,but high level of lipid would exceed the metabolic capacity of eel and cause liver damage,resulting in increased blood lipid and metabolic disorder.Feed lipid level has a significant effect on blood glucose and liver glycogen content(P<0.05),indicating that excessive lipid level may affect the body’s absorption and utilization of sugar.(3)Superoxide dismutase(SOD)and catalase(CAT)activity in the serum of each test group increased first and then decreased,and SOD activity in L4 group was the highest.Malondialdehyde(MDA)activity in serum of L7 group was significantly higher than that of the other six groups,indicating that appropriate lipid level can improve the antioxidant capacity and immune ability of the body,and high lipid level will increase the content of peroxide in the body,causing certain negative effects.(4)The activity of amylase,protease and lipase in liver and pancreas of eel increased first and then decreased with the increase of lipid level.The activity of digestive enzymes in the intestinal tract showed a decreasing trend,indicating that appropriate lipid content could induce the secretion of digestive enzymes in hepatopantalis,but high lipid level might damage the structure of the liver and affect the secretion or inhibit the activity of digestive enzymes.(5)With the increase of lipid level,the crude lipid content of whole fish,liver,intestinal tract,muscle and skin in each test group showed an upward trend,andthe increase of the crude lipid content of skin was the largest,indicating that the increase of feed lipid level would make the lipid in the body of eel deposit in various tissues,but when the lipid level is high,in order to avoid too much lipid deposition in the liver,it will be stored in the skin,which is more beneficial to the fish.(6)By observing the microstructure and ultrastructure of each experimental group,it was found that the liver tissue structure would be damaged when the lipid level was highThe results showed that the fat level in the feed can promote the growth of jaundice,the body’s lipid metabolism is active,the sugar metabolism is normal,and the body’s normal antioxidant capacity and immunity can be maintained.However,if the fat level is too high,it will exceed the metabolic capacity of jaundice and cause lipid elevation and lipid metabolism.Disorders may also affect the body’s absorption of sugar and hepatic glycogen storage,increase the body’s peroxide content,and damage liver cells,causing jaundice fatty liver,etc.,affecting the secretion and vitality of digestive enzymes in related organs,and reducing the absorption and absorption of jaundice.Ability to increase the feed coefficient,slow the growth of jaundice,and reduce the quality of jaundice.The use of fish oil soybean oil as a fat source of Astragalus feed suitable for adding fat levels of 7.03% ~7.68%. |
