Effects Of Lipoic Acid On Growth Performance,Antioxidant Profile And Lipid Metabolism Of The GIFT Tilapia (Oreochromis Niloticus)

Tilapia,which was called“white salmon”,was recognized as an alternative to quality marine fish.Tilapia species constitute the second most important group of fish in global aquaculture due to their fast growth rate,disease resistance and marketability.The availability of the complete genomic information on tilapia has enabled scientists to improve further their productivity in aquaculture.For tilapia cultivation,providing efficient and environmentally friendly feed for its growth and development is undoubtedly the most critical part.In order to improve the utilization efficiency of dietary protein and reduce the pollution of nitrogen metabolism to water environment,high-fat diet is widely used in production practice of fish to save dietary protein.However,high-fat diet will cause excessive lipid accumulation,causing a variety of metabolic diseases,which will do harm to the growth and health of fish.As a functional additive with strong antioxidant properties,lipoic acid is involved in the regulation of energy metabolism,which can reduce the accumulation of triglycerides and weaken the oxidative stress in animals.Therefore,this study evaluated the interaction between different dietary lipid levels and?-lipoic acid,the optimum amount of?-lipoic acid in high-fat diet and the saving effect on dietary protein.The research results can provide a basic reference for further research and application of lipoic acid.The main results and conclusions are as follows:1 Effects of?-lipoic acid on growth performance,antioxidant profile and lipid metabolism of the GIFT tilapia?Oreochromis niloticus?fed diets containing diverse lipid levelsIn order to evaluate the effects of?-lipoic acid on GIFT tilapia?Oreochromis niloticus?fed diets containing diverse lipid levels,a total of six isonitrogenous diets were formulated with 6%and 12%dietary lipid contents and 0,600 and 1200 mg/kg?-lipoic acid levels?abbreviated as L6-0,L6-600,L6-1200;L12-0,L12-600,L12-1200,respectively?,and fed to juveniles?9.56±0.06 g?for 8 weeks.Results showed that the weight gain?WG?of fish improved significantly in the L12-600 than the L12-0;The feed conversion ratio?FCR?of fish decreased significantly in the L12-600 than the L12-0;The hepatosomatic index and intraperitoneal fat index of fish fed on L12-600 and L12-1200 diets were significantly lower than those fed on the L12-0diet;The content of crude lipid in fish decreased significantly in L12-1200compared to the L12-0.The activities of superoxide dismutase?SOD?and the content of reduced glutathione?GSH?in liver were significantly higher in fish fed on the L12-600 diet than those fed on the L12-0diet.The activities of glutathione peroxidase?GSH-Px?in serum and liver were significantly higher in fish fed on the L12-600 diet than the control?L12-0?.The malondialdehyde?MDA?content in serum and liver was significantly lower in L12-600 than in the control?L12-0?.The TG content in the liver of fish decreased significantly in L12-1200 compared to the L12-0.The adipose triglyceride lipase gene?ATGL?was significantly up-regulated in fish fed on the L12-600 and L12-1200 diet compared to L12-0;But the diacylglycerol acyltransferase2 gene?DGAT2?was significantly down-regulated in L12-1200compared to L12-0;The liver-type fatty acid-binding protein?L-FABP?gene and acyl-coenzyme A oxidase gene?ACO?of fish were significantly up-regulated in L12-1200 compared to L12-0.The research indicated that the appropriate amount of?-LA supplementation in the diet can improve growth performance and relieve lipid oxidative damage by accelerating lipid catabolism and reducing lipid synthesis of juvenile GIFT tilapia.2 Effects of?-lipoic acid on growth performance,antioxidant profile and lipid metabolism of the GIFT tilapia?Oreochromis niloticus?fed high fat dietsThe wide use of lipid as a non-protein energy substitute has led to lipid metabolic problems in cultured tilapia,such as abnormal lipid metabolism,fatty liver and intolerance to stress.Therefore,studies that reduce the effects of high-fat diets in genetically improved farmed tilapia?GIFT?are required.This study evaluated the optimum level and effects of dietary?-lipoic acid??-LA?on growth performance,body composition,antioxidant capacity and lipid metabolism of GIFT tilapia.The basal diet(120 g kg^-1 lipid)was supplemented with six concentrations of?-LA at 0?control?,L300,L600,L900,L1200 and L2400 mg kg^-1 diet to make the experimental diets,which were fed to GIFT tilapia juveniles?initial body weight:0.48±0.01 g?for eight weeks.The weight gain?WG?of fish improved significantly in the L300 than other dietary treatments.The intraperitoneal fat index and lipid content of fish fed on the L2400 diet decreased significantly than those fed on the control diet.The activities of superoxide dismutase?SOD?and glutathione peroxidase?GSH-Px?in serum and liver were significantly higher in fish fed on the L300 diet than the control.The reduced glutathione?GSH?content of fish fed on the L300 in serum and liver were significantly higher than those fed on control diet.The malondialdehyde content in serum and liver was significantly lower in L300 than in the control.The adipose triglyceride lipase gene was significantly up-regulated in fish fed on the L2400 but the diacylglycerol acyltransferase2 gene was down-regulated in adipose.The liver-type fatty acid-binding protein?L-FABP?gene in the liver was significantly up-regulated in fish fed on the L300 and L600 diets.Moreover,the acyl-coenzyme A oxidase gene in liver was significantly up-regulated in fish fed on the L300,L600,L900 and L1200diets.Polynomial regression analysis indicated that 439 to 528 mg kg^-1?-LA is an appropriate dosage in high-fat diet to improve growth performance and relieve lipid oxidative damage by accelerating lipid catabolism and reducing lipid synthesis in GIFT tilapia.3 Effects of dietary protein-to-lipid ratio and?-lipoic acid on the growth performance,body composition and digestive enzyme activities of the GIFT tilapia?Oreochromis niloticus?.An 8-week feeding trial was conducted to evaluate the effects of dietary protein-to-lipid ratio and?-lipoic acid on growth performance,body composition and digestive enzyme activities of the GIFT tilapia?Oreochromis niloticus?.Five isoenergetic diets were formulated containing three protein-to-lipid ratios?34/6,30/8,26/10?and two?-lipoic acid concentrations?0 and 300mg/kg diet?,diet with 34/6protein-to-lipid ratio without?-lipoic acid addition was the control diet?D0?,diets with 30/8 and 26/10 protein-to-lipid ratios containing 0 and 300mg/kg?-lipoic acid were abbreviated as D1,D2,D3,D4,respectively.Five hundred and twenty five juvenile tilapia averaging 0.86±0.01 g were randomly allotted to 15 aquariums?5treatments in triplicate groups?and fed the test diets at a feeding rate of 4%body mass daily.The results showed significant decrease of final body weight?FBW?,weight gain?WG?and specific growth rate?SGR?of fish fed on D3 diet compared to D0.And feed conversion ratio?FCR?was significantly increased of fish fed on D3 diet compared to D0.The FBW of fish in D4 was significantly increased but the FCR was significantly decreased compared to D3.Compared to D0 and D1,the hepatosomatic index?HSI?and intraperitoneal fat index?IPF?of fish in D3 were significantly increased.But the HSI of fish in D4 was significantly decreased compared to D3.With the decrease of dietary protein-to-lipid ratio from 34/6 to 26/10,the crude protein content of whole fish decreased significantly while the crude lipid content increased significantly.For the lipid content of fish,D4 was significantly lower than D3,and D2 was significantly lower than D1.The activity of lipase in liver was significantly lower in fish fed D3 diet than in D0 and D1.The activity of amylase in liver was significantly lower in fish fed D3 and D1diet than in D0,while D2 was significantly higher than D1.The research indicated that the growth performance,body composition and digestive enzyme activities of the GIFT tilapia were affected by dietary protein-to-lipid ratio and?-lipoic acid.300 mg kg^-1 dietary?-lipoic acid addition is a recommended dose in the diet for GIFT tilapia fed on 30/8protein-to-lipid ratio diets.