| To research the appropriate lipid requirement of bighead carp,a 60 days growth trial was conducted in the indoor recirculating aquaculture system to study the effects of dietary lipid levels on the growth,body composition,fatty acid composition of muscle,digestive enzyme activities and intestinal tissue of bighead carp.The trial was single-factor gradient design.High quality casein and fish meal were used as the main protein source,corn oil and soybean oil,mixed1:1,were used as the main lipid source.Isonitrogenous diets were formulated to contain six graded levels of lipid respectively,such as 0,3%,6%,9%,12% and 15%,which fat content were 4.72%,7.31%,11.02%,14.90%,11.02% and 19.37%.The test subject were bighead carp with average initial body weight 3.28 ± 0.11 g,divided into six groups,with three replicates of 20 fish in each replicates.The results were summarized as follows:1.The growth test showed that dietary lipid levels have a significant impact on the growth of bighead carp(P<0.05).In the range of 4.72% to 19.37%,with the increase of dietary lipid level,the weight gain rate and specific growth rate of bighead carp were increased firstly and decreased then.When feed lipid level was 11.02%,the growth rate and specific growth rate of bighead carp reached the maximum value,which were significantly higher than14.90% group,17.14% group and14.90% group(P<0.05).It determine that when dietary lipid level were 7.77% ~ 8.31%,the weight gain rate and the specific growth rate reached the maximum value by regression analysis.It showed that when dietary fat content was in the range of 7.77% to 8.31%,the bighead carp with initial body weight of 3.28 ± 0.11 g are grew fastest.2.The dietary lipid levels have significant influences on the body composition of bighead carp(P<0.05).(1)When dietary fat content was from 4.72% to 17.14%,significant increase in the body lipid content(P<0.05).When the dietary fat level was more than 17.14%,crude fat content of whole fish decreased obviously(P<0.05).(2)With the increase of dietary lipid level,the crude protein content of fish increased firstly and decreased then.When the dietary fat level was higher than 14.90%,the crude protein content of the whole fish showed a downward trend.(3)moisture,the ash content and moisture content were increased firstly and decreased then.(P<0.05).When dietary lipid level was higher than 11.02%,increased in crude ash content.and moisture content of body.These results suggestededed that when dietary lipid content was higher than 17.14%,the protein content in body would reduced,while the crude ash and moisture content in body would increased.3.The dietary lipid levels and dietary fatty acid composition had a significant influence on the fatty acid composition in muscle of bighead carp(P<0.05).(1)With the dietary lipid level increased,the C14:0,C16:0andC18:0content of muscle were all decreased significantly(P <0.05),consistent with the content of corresponding group feed.(2)With the increase of dietary lipid level,significant decreases in the content of C16:1andC18:1n9(P<0.05).(3)With the dietary lipid level increased,the total content of PUFA was increased significantly(P<0.05),which similar to the change of corresponding group feed.(4)when the dietary lipid level from 4.72% increase 17.14%,C18:3n-3 content in muscle increased significantly,however,decreased the content of C18:3n-3,with the dietary lipid level continue increase.The Dietary lipid level had no significant effects on C20:5n3(EPA),C22:6n3(DHA)content of muscle(P>0.05).(5)With the dietary lipid level increase,the content of C18:3n6 and C20: 3n6 in muscle increase,which was contrast with the corresponding feed group.Lipid levels showed no significant effect on the content of C20:4n6 in muscle for all group(P>0.05).With the dietary lipid level increase,the total content of n-6PUFA in muscle increased(P<0.05),and it was consistent with corresponding groupfeed.(6)With the dietary lipid level increase,the ratio of n-3PUFA/n-6PUFA decreased firstly and increased then,which was similar to the trend of corresponding group feed.These results suggesteded that dietary fat content and fatty acid composition would affect the muscle fatty acid composition and content of bighead carp.4.Bighead has the ability that transforming feed fatty acid into fatty acids in muscle.SFA content in muscle was lower than it in feed corresponding.The proportion of MUFA in muscle was significantly higher than that in corresponding feed.Although the proportion of 18C:2n-6 in muscle was lower than it in corresponding group feed,the proportion of C20:4n-6 in muscle was higher than it in corresponding diet group.The C20:3n-3 was found in muscle,but it was not detected in the corresponding feed group.5.In the range of 4.72%~11.02%,with the dietary fat level increased the amylase activity showed a increasing trend in foregut,hindgut and liver.However,when the dietary fat level in the range of 11.02%~19.37%,amylase activity showed a downward in those tissues and organs.When the dietary lipid level was 11.02%,the protease activity reached the highest level.When dietary fat level was 4.72%~11.02%,no significant difference were found between the groups(P>0.05),although the protease activity were all increased in foregut,hindgut and the liver.When the lipid level was higher than 11.02%,decreased in protease activity of foregut,hindgut and liver.These results suggested that it can promote the secretion of protease and amylase in liver and intestine,when the dietary lipid content was 4.72%~11.02%.6.When dietary lipid level increased from 4.72% to 11.02%,intestinal length ratio of bighead was increased.It showed a decreasing trend,when the lipid level in the range of 11.02%~19.37%.When the dietary lipid level was 11.02%,intestinal length ratio of bighead reached the highest value,significantly higher than the other five groups(P<0.05).With the increase of dietary lipid level,bighead intestinal villus height increased,the number of goblet cells increased firstly and decreased then.When the feed fat level was higher than 11.02%,the number of goblet cells decreased.It showed thatwhen the fat diet was 11.02%,the ratio of intestine length increased,the number of goblet cells increased.When dietary fat levels was greater than 11.02%,the number of goblet cells in the intestinal mucous layer slightly reduced.According to the above results,when feed fat level within the scope of 4.72%~11.02%,it could conducive the development of intestinal tissue,promoted digestive enzyme secretion,improved the digestive ability,improve the proportion of polyunsaturated fatty acid in muscles,promoted growth.The weight gain rate,specific growth rate as the main indicators,through quadratic regression analysis show that the appropriate lipid requirements was7.77%~8.31% for 3.28 g bighead carp. |
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