Effects Of Lipid Content,n-6 Fatty Acids And Astaxanthin In The Diet On Growth Performance And Lipid Metabolism Of Juvenile Tiger Puffer(Takifugu Rubripes)

This study was conducted to investigate the effects of lipid content,n-6 fatty acids and astaxanthin in the diet on growth performance and lipid metabolism of juvenile tiger puffer(Takifugu rubripes).These studies were aimed at investigating the mechanisms involved in the utilization of lipid,n-6 PUFA and astaxanthin in tiger puffer(Takifugu rubripes).The results and conclusion are summarized as follows:1.A moderately high level of dietary lipid inhibited the protein secretion function of liver in juvenile tiger puffer Takifugu rubripesTiger puffer have a unique lipid storage pattern.They store lipid predominantly in liver.To investigate the hepatic physiology of tiger puffer in response to a moderately high level of dietary lipid,a 74-day feeding trial was conducted,followed by a hepatic transcriptome assay.Two experimental diets which had an optimal(10.44%,Control)or moderately higher(14.64%,high-lipid diet,HL)dietary lipid level was formulated.Each diet was fed to triplicate tanks.No significant difference was observed in growth and feed efficiency between the two groups,but the survival was significantly lower in group HL.The HL diet also resulted in significantly higher lipid accumulation in liver,which was reflected in the hepatic histology.The biochemical parameters in serum confirmed the existence of stress in liver caused by high lipid intake.A total of 63 differentially expressed genes between groups were observed in the hepatic transcriptome assay,which were primarily enriched in Gene Ontology(GO)terms such as Endopeptidase activity,Secretion,and Organic acid transport,as well as in Kyoto Encyclopedia of Genes and Genomes(KEGG)pathways such as Protein processing in endoplasmic reticulum and DNA replication.The HL diet tended to inhibit the protein synthesis and secretion in liver,and this was evidenced by activities/concentrations of selected proteins secreted into intestine.Genes related to liver protection and repair were transcriptionally stimulated by diet HL.In conclusion,compared to the optimal lipid requirement,a moderately higher lipid level in the diet for tiger puffer did not compromise the growth performance,but tended to inhibit the protein secretion function of liver and stimulate the processesrelated to liver protection and repair.The present results will be beneficial to both feed management in tiger puffer farming and elucidation of lipid metabolism characteristics in fish which store lipid in liver.2.N-6 polyunsaturated fatty acids are less efficiently utilized than saturated fatty acidsc in the marine teleost,tiger puffer Takifugu rubripesA 74-day feeding trial was conducted to investigate the efficacy of n-6polyunsaturated fatty acid(PUFA)in diets for tiger puffer.Six experimental diets with graded levels of n-6 PUFA replacing saturated fatty acids(SFA)were formulated.Each diet was fed to triplicate tanks of 30 fish.Increasing levels of dietary n-6 PUFA resulted in decreased weight gain,feed efficiency,and crude protein content in fish,but increased lipid accumulation in whole fish and liver.Liver samples from fish fed the lowest and highest level of dietary n-6 PUFA(group D1 and D6 respectively),which had most significant difference in growth performance,were subjected to transcriptomic assay to gain more insight into the nutritional activity of n-6 PUFA.Compared to D1,diet D6 up-and down-regulated transcription of 1948 and1961 genes respectively.Analysis of the differentially expressed genes showed that high dietary levels of n-6 PUFA(concurrently low levels of SFA)tended to induce glycolysis and triacylglycerol biosynthesis,but reduce synthesis of amino acid and protein,and cause impairment to liver health.The mitochondrial DNA copy number,activity of mitochondrial respiratory chain complex I,and glycogen content in the liver,which indicate energy supply status,significantly decreased with increasing levels of dietary n-6 PUFA.In conclusion,compared to SFA,n-6 PUFA were less efficiently utilized in tiger puffer.High n-6 PUFA/SFA ratios in diet led to reduced energy supply and abnormal lipid accumulation in the liver,which probably consequently negatively affect protein synthesis,liver health and growth of tiger puffer.3.Dietary astaxanthin differentially affected the lipid accumulation in the liver and muscle of the marine teleost,tiger puffer Takifugu rubripesThe lipidregulating effects of astaxanthin(ASTX)have been widely reported in terrestrial animals.However,little relevant information has been available in fish although ASTX has been used as exogenous pigment and antioxidant in fish feed.A74-day feeding study was conducted to investigate the effects of dietary ASTX on lipid accumulation in the marine teleost tiger puffer.Four experimental diets differing only in ASTX supplementation,that is,0(control),50(ASTX50),100(ASTX100)and 500(ASTX500)mg/kg,were randomly assigned to 12 tanks of juvenile tiger puffer.Compared to control,the liver lipid content in group ASTX50 was significantly higher,while those in groups ASTX100 and ASTX500 were lower.The muscle lipid contents in group ASTX500 were significantly higher compared to control.Group ASTX50 had the best growth performances,while diet ASTX500 seemed to have adverse effects.In the liver,compared to control,groups ASTX50 and ASTX100 showed significantly lower mRNA expressions of genes related to triglycerol synthesis and fatty acid synthesis,transport and uptake,but higher expressions of genes related to β-oxidation and monoglycerol hydrolysis.In the muscle,compared to control,ASTX100 showed higher expressions of genes related to β-oxidation.ASTX50 resulted in higher contents of saturated and monounsaturated fatty acids but lower contents of n-3 polyunsaturated fatty acids in fish.In conclusion,astaxanthin in diets for tiger puffer differentially regulated the lipid accumulation in the liver and muscle,both in dose-dependent manners.Excess dietary astaxanthin(500 mg/kg)had adverse effects on tiger puffer.