Effect Of Different Dietary Lipid Levels On The Growth Performance,Antioxidantion,Immunity,Fatty Acid Metabolism And Related Gene Expression In Juvenile Gifi Tilapia

The objectives of this study were to investigate the effect of different dietary lipid levels on the growth performance,antioxidantion,immunity,fatty acid metabolism and related gene expression in juvenile genetic improvement farmed tilapia(GIFT,Oreochromis niloticus).Six groups of the juveniles with 40 d of age in triplicate were fed for 90 days using six iso-nitrogen(34% dietary protein)diets with different lipid levels: 0.35%(control),3.35%,6.35%,9.35%,12.35%,and15.35% adjusted by adding fish oil.The juveniles were fed in the tanks with 36 juveniles in a tank with volume of 120 L.Fish samples were respectively taken and analyzed at 0 day and 90 days and the main results were:1.The different dietary lipid levels significantly improved the growth performance of juvenile GIFT tilapia.Compared with juvenile GIFT tilapia in control group(0.35% lipid),the specific growth rate(SGR),daily growth index(DGI),weight gain rate(WGR),body length growth rate(BLG)and protein efficiency(PER)of juvenile GIFT tilapia in lipid supplementation groups were significantly increased(P < 0.05)and the feed conversion rate(FCR)was significantly decreased(P < 0.05).However,the survival rate of juvenile GIFT tilapia in lipid supplementation groups had no significant influence(P > 0.05).According to quadratic polynomial regression analysis,the SGR was the highest when the dietary lipid level was 10.52%.The DGI was the highest when the dietary lipid level was 10.58%.The WGR was the highest when the dietary lipid level was 10.67%.The BLG was the highest when the dietary lipid level was11.56%.The PER was the highest when the dietary lipid level was 10.55%.The FCR was the lowest when the dietary lipid level was 10.61%.This is to say,juvenile GIFT tilapia showed the better growth performance when the dietary lipid level was 10.52-11.56%.2.The different dietary lipid levels significantly affected the body indicators of juvenile GIFT tilapia,including condition factor(CF),hepatosomatic index(HSI)and visceral index(VSI)(P < 0.05).According to the quadratic polynomial regression analysis,CF was the highest when the dietary lipid level was 10.54%.HSI was the lowest when the dietary lipid level was 7.56%.VSI was lowest when the dietary lipid level was 4.53%.The different dietary lipid levels significantly affected the body composition of juvenile GIFT tilapia.Compared with juvenile GIFT tilapia in control group(0.35% lipid),the crude fat content of whole fish of juvenile GIFT tilapia in lipid supplementation groups was significantly increased(P < 0.05)while the crude protein content of whole fish of juvenile GIFT tilapia in lipid supplementation groups was significantly decreased(P < 0.05).However,the total water content and ash content of whole body of juvenile GIFT tilapia in lipid supplementation groups had no significant effect(P > 0.05).The different dietary lipid levels significantly decreased the activity of lipase and fatty acid synthase(FAS)of juvenile GIFT tilapia.Compared with juvenile GIFT tilapia in control group(0.35% lipid),the lipase activity in intestine and FAS activity in liver,muscle and mesenteric adipose tissue of juvenile GIFT tilapia in lipid supplementation groups were significantly decreased(P < 0.05).In juvenile GIFT tilapia,the activity of lipase was as follows: foregut > midgut >hindgut;The activity of fatty acid synthase was as follows: liver > mesenteric adipose tissue > muscle.3.The different dietary lipid levels significantly increased the antioxidant capacity,immune function and inflammatory inhibition ability of juvenile GIFT tilapia.Compared with juvenile GIFT tilapia in control group(0.35% lipid),the activity of superoxide dismutase(SOD),total antioxidant capacity(T-AOC),glutathione peroxidase(GSH-Px)and catalase(CAT)in liver and serum of juvenile GIFT tilapia in lipid supplementation groups were significantly improved(P < 0.05),the content of malondialdehyde(MDA)in liver and serum of juvenile GIFT tilapia in lipid supplementation groups was significantly decreased(P <0.05),the spleen index of juvenile GIFT tilapia in lipid supplementation groups was significantly improved(P < 0.05),the activity of lysozyme(LZM)and alkaline phosphatase(ALP)and the content of C3 and immunoglobulin M(Ig M)in serum of juvenile GIFT tilapia in lipid supplementation groups were significantly improved(P < 0.05).Compared with juvenile GIFT tilapia in control group(0.35% lipid),the relative expression levels of tumor necrosis factor ?(TNF-?),interleukin-1?(IL-1?)and interferon ?(INF-?)genes in spleen,head kidney and liver of juvenile GIFT tilapia in lipid supplementation groups were significantly decreased(P < 0.05).4.The different dietary lipid levels significantly affected the fatty acid composition of juvenile GIFT tilapia.Compared with juvenile GIFT tilapia in control group(0.35% lipid),the content of n-3 polyunsaturated fatty acids(n-3PUFAs)in the tissues/organs of juvenile GIFT tilapia in lipid supplementation groups were significantly increased(P < 0.05),the content of saturated fatty acid(SFAs)and monounsaturated fatty acid(MUFAs)in liver,muscle,kidney,mesenteric adipose tissue,serum and brain of juvenile GIFT tilapia in lipid supplementation groups were significantly decreased(P < 0.05),the content of polyunsaturated fatty acid(PUFAs)in liver,muscle,kidney,mesenteric adipose tissue,serum and brain of juvenile GIFT tilapia in lipid supplementation groups were significantly increased(P < 0.05).In experimental groups,the content of n-6 polyunsaturated fatty acids(n-6 PUFAs)in each tissue/organ was decreased with the increase of dietary lipid levels.In juvenile GIFT tilapia,PUFAs content in the same tissue/organ of juvenile GIFT tilapia were significantly higher than that of SFAs content and MUFAs content(P < 0.05).Compared with different tissues/organs,fatty acid composition in liver and muscle of juvenile GIFT tilapia was easily affected by dietary fatty acid composition.5.The different dietary lipid levels significantly affected the relative expression of lipid sensitive genes of juvenile GIFT tilapia.Compared with juvenile GIFT tilapia in control group(0.35% lipid),the leptin concentration in serum of juvenile GIFT tilapia in lipid supplementation groups was significantly improved(P < 0.05),while leptin concentration in serum was significantly decreased(P < 0.05).The relative expression of PPAR? gene,leptin gene and adiponectin receptor gene 1/2(Adipo R1/2)in the tissues/organs of juvenile GIFT tilapia in lipid supplementation groups were significantly increased(P < 0.05),while the relative expression of leptin receptor gene and adiponectin gene in the tissues/organs of juvenile GIFT tilapia in lipid supplementation groups were significantly decreased(P < 0.05).In juvenile GIFT tilapia,the PPAR? gene mainly expressed in the liver,brain and heart.Leptin gene mainly expressed in the brain and liver,and leptin receptor gene mainly expressed in the brain,spleen,heart.Adiponectin gene mainly expressed in the liver and the brain,Adipo R1 gene mainly expressed in the spleen,heart and liver and Adipo R2 genes mainly expressed in the brain,liver and muscle.It was concluded that the different dietary lipid levels could significantly affect the growth performance,antioxidantion,immunity,fatty acid metabolism and the expression of related gene in juvenile GIFT tilapia.When the dietary lipid level was 10.52-11.56%,the juvenile GIFT tilapia showed the better growth performance.