Effect Of Nano-selenium On Muscle Quality Of Grass Carp Fed With High-fat Diet And The Influence Of Overwintering On The Health Of Liver And Intestine

The use of High-fat diet（HFD）is one of the important means to reduce feed costs and obtain higher economic benefits in aquaculture,but long-term intake of HFD will bring negative effects on the health and quality of fish.Selenium,as an antioxidant,can regulate the enzymatic reaction and oxidation-reduction balance,and participate in the metabolism of protein,lipid and carbohydrate.In this study,the grass carp（Ctenopharyngodon idella）were fed with HFD to investigate the regulatory effects and mechanisms of selenium on the deposition of muscle nutrients and the formation of muscle fibers.In addition,the effect and mechanism of selenium on improving the health of hepatopancreas and intestines after overwintering of grass carp fed with HFD were also evaluated.This study aimed to provide reference for nutritional regulation on flesh quality and overwintering on hepatopancreas and intestine health of grass carp fed with HFD.The main conclusions are as follows:Trial 1.This study aims to confirm the positive effects of dietary nano-Se on nutrients deposition and muscle fiber formation in grass carp fed with HFD and to reveal its possible molecular mechanism.The lipid deposition,protein synthesis and muscle fiber formation of grass carp fed with RD,HFD and HFD supplemented with nano-Se（0.3 and 0.6 mg/kg）for60 d were tested.Results show that nano-Se significantly reduced lipid content,dripping loss and fiber diameter（P<0.05）,but increased protein content,post-mortem p H_24h and muscle fiber density（P<0.05）in muscle of grass carp fed with HFD.Notably,dietary nano-Se decreased lipid deposition in muscle by regulating the activity of AMPK protein kinase,and increased protein synthesis and fiber formation in muscle by activating the target of rapamycin（TOR）and Myogenic determinationgene（Myo D）factor pathways.Therefore,dietary nano-Se can regulate the nutrients deposition and muscle fiber growth in grass carp fed with HFD,which exhibit potential benefit for improving flesh quality of grass carp fed with HFD.Trial 2.This study aims to explore the positive effect of nano-Se on the health of grass carp after overwintering,and reveal its possible molecular mechanism.At the end of the first experiment,some grass carp in the RD,HFD,HSe0.3 and HSe0.6 groups were randomly selected and retained for a 105-day overwintering trial.After the trial,the health status of hepatopancreas and intestines of grass carp was comprehensively evaluated.The results showed that nano-Se significantly reduced the content of serum glutamic oxaloacetic transaminase（GOT）,glutamic pyruvic transaminase（GPT）and malondialdehyde（MDA）after overwintering of grass carp fed with HFD（P<0.05）,and significantly increased the catalase（CAT）activity in hepatopancreas（P<0.05）.Meanwhile,nano-Se also significantly increased the villi height and lipase activity in intestine of grass carp fed with HFD after overwintering（P<0.05）.Moreover,nano-Se enhanced the barrier function of intestine by up-regulating gene expression of intestinal tight junction protein（ZO-1、Occludin、Claudin-3）,and down-regulating gene expressions of inflammatory signal pathway（TLR2、TLR4、p38 MAPK、NF-κB p65）and pro-inflammatory factors（IL-8、IL-1β、IFN-γ、TNF-α、IL-6）in hepatopancreas and intestine.Besides,up-regulating gene expression of the anti-inflammatory factor（IL-10）and antioxidant related factors（GPx4a、GPx4b）,so as to alleviate the inflammation and oxidative stress in the hepatopancreas and intestine of grass carp after overwintering.Therefore,nano-Se could reduce the inflammation and oxidative stress of hepatopancreas and intestine of grass carp fed with HFD after overwintering,thus promoting the health of hepatopancreas and intestine of grass carp.In summary,nano-Se can improve the nutritional value of grass carp fed with HFD by reducing lipid deposition in muscle,increasing the Se content and protein deposition in muscle,and improve the texture characteristics of grass carp fed with HFD by promoting the formation of muscle fibers.In addition,nano-Se can also improve the health of hepatopancreas and intestine of grass carp fed with HFD after overwintering,and reduce the adverse effects of low temperature and starvation on grass carp during the overwintering period.