Effects Of Dietary N-3/n-6 Polyunsaturated Fatty Acid Ratio On Growth,fat Metabolism And Intestinal Health In Lateolabrax Maculatus

The experiment was conducted to investigate the effects of dietary n-3/n-6 polyunsaturated fatty ratio on growth,fat metabolism and intestinal health of Lateolabrax maculatus.The linoleic acid,DHA and EPA as fat sources,6 diets with n-3/n-6 PUFA ratio of 10(n-3),2,1,0.5,0.25 and 0.05(n-6)were prepared,360 Lateolabrax maculatus(initial body weight: 11.06 ± 0.2 g)were randomly divided into 18 aquariums,3 aquariums were fed with each kind of feed.The trial period was 8 weeks.The relevant samples were collected and determined.The main results were as follows:1.Effects of n-3/n-6 PUFA ratio on growth performance and body composition of Lateolabrax maculatusThe results showed that the ratio of n-3/n-6 PUFA significantly affected the growth performance of Lateolabrax maculatus.When the ratio of n-3/n-6 was 0.5,the final body weight,weight gain and specific growth rate of the fish were the maximum.All treatments had no significant difference in feed conversion rate(P>0.05),hepatosomatic index,viscerosomatic index and condition factor(P>0.05).The contents of C20:4n-6,EPA and DHA were decreased significantly with the decrease of the ratio of n-3/n-6,but the contents of C18:1n-9 and C18:2n-6increased significantly,the fatty acid composition of the muscle was positively correlated with the fatty acid composition of the feed.2.Effects of n-3/n-6 PUFA ratio on fat deposition and metabolism of Lateolabrax maculatusWith the decrease of dietary n-3/n-6,the content of serum total cholesterol and triglyceride significantly increased(P<0.05).and the activity of serum aspartate aminotransaminase significantly decreased when the ratio was 0.5～1(P<0.05).In addition,the intraperitoneal fat index of Lateolabrax maculatus increased with the decrease of n-3/n-6,and reached the maximum in n-6.In hepatocyte tissue morphology,the nuclei of hepatocytes deviated,vacuolated seriously and fat droplets appeared in n-6.With the decrease of n-3/n-6,the gene expression of FAS and ACC were significant up-regulated,while the gene expression of PPARa,ATGL and CPTI were up first and then going down.With the decrease of dietary n-3/n-6,the activity of liver Catalase increased at first and then decreased,and reached the maximum in n-3/n-6 was 0.5,however,all treatments no significant difference in superoxide dismutase,total antioxidant capacity and malondialdehyde content(P>0.05).To sum up,n-6 PUFA can lead to fat deposition of Lateolabrax maculatus,which may be increase fat synthesis gene expression,and n-3 PUFA can up-regulation of lipolysis gene expression to reducing fat deposition,and increase energy supply for fish body.3.Effects of n-3/n-6 PUFA ratio on intestinal digestive enzymes,inflammation and composition of microflora in Lateolabrax maculatusWith the decrease of n-3/n-6,the activities of trypsin and lipase in the intestine of Lateolabrax maculatus increased at first and then decreased(P<0.05),and reached the maximum when the ratio of n-3/n-6 was 0.5 and 1,respectively.In n-6,the gene expression of IL-6 and TNF-α was the highest(P<0.05),while the gene expression of IL-4 and IL-10 increased first and then decreased with the decrease of n-3/n-6(P<0.05).The gene expression of IL-4 and IL-10 in n-6 was significantly lower than n-3(P<0.05),while the gene expression of IL-10 increased when n-3/n-6 was 0.5～2 compared with n-3(P<0.05).The results showed that with the decrease of n-3/n-6,the number of intestinal OTU increased at first and then decreased,the Chao1 index increased and Shannon index decreased(P<0.05),indicating that n-3/n-6 could increase the relative abundance of intestinal microflora of Lateolabrax maculatus,reducing species diversity.At phylum level,the abundance of firmicutes and bacteroidetes decreased when n-3/n-6 was 0.25 compared with n-3,and at genus level,the abundance of enterococcus increased significantly with the decrease of n-3/n-6(P<0.05).In conclusion,excessive n-6PUFA can decrease the activity of digestive enzymes and induce intestinal inflammation,which broke the composition of intestinal flora,and affect the intestinal health of Lateolabrax maculatus.Dietary n-3/n-6 between 0.5 to 1,which help maintain the intestinal health of Lateolabrax maculatus.