Screening Of Dietary Lipid Sources And Lipid Metabolic Regulation Of Red Swamp Crayfish,Procambarus Clarkii

The optimization of feed formulations is an effective strategy to promote growth or health of aquatic animals and improve economic and ecological benefits.The lipid source is another important energy substance in the feed formulations in addition to the protein source and carbohydrate source,providing energy for the animals and participating in the body composition.It is generally believed that fish oil is the most suitable source of lipid for aquatic animals,but the current shortage makes research on alternative lipid source very necessary.There have been many reports on study about fish oil replacement in fish,but few studies have been done on crustaceans,especially on red swamp crayfish,Procambarus clarkii.Therefore,in this thesis,we set Procambarus clarkii(also known as crayfish)as experimental animal,and made the best of the Animal Physiology,Molecular Biology or Aquatic Animal Nutrition to explore the effects of different lipid sources on the growth,lipid metabolism,antioxidant ability and immunoregulation of crayfish,initial screening of a more suitable lipid source other than fish oil.Based on this,resveratrol was added into the diets to evaluate whether it works on lipid regulation of crayfish at first attempt.The primary research details and results of this thesis are as follows:Experiment 1 Dietary lipid sources modulate the intestinal transport of fatty acids in the red swamp crayfish Procambarus clarkiiThe influence of different dietary lipid sources on fatty acid absorption,synthesis,and transport in the crayfish was investigated.Six isonitrogenous and isocaloric diets were set as follows:fish oil(FO),corn oil(CO),rapeseed oil(RO),soybean oil(SO),palm oil(PaO),and beef tallow(BT)served as lipid sources.The results showed that the crayfish fed FO,SO or BT obtained a significant higher weight gain rate(WGR),specific growth rate(SGR)and lower feed conversion ratio(FCR)compared to PaO.Tissue FA profiles highly reflected on the FA in the diets,Low contents of total triglyceride(TG)and total cholesterol(TC)were observed in the hemolymph and hepatopancreas of crayfish fed FO or BT diet.In the lipid anabolism pathway,fatty acid synthase(fas),sterol regulatory element binding protein 1(srebp1),and retinoid X receptor(rxr)were down-regulated by dietary FO while up-regulated by some vegetable oils.The gene involved in fatty acid(FA)uptake and transport,fatty acid binding protein(fabp),was up-regulated by CO in the hepatopancreas and by BT in muscle.With respect to intestinal fatty acid transporters,fatty acid transport protein 4(FATP4)was up-regulated by BT diet,diacylglycerol transferase1(DGAT1)was down-regulated by FO or BT diet,and Niemann-Pick C1-like 1(NPC1L1)was down-regulated in the SO diet.Whereas,apolipoprotein B-48(Apo B-48)and fatty acid translocase(FAT/CD36)were not changed by dietary lipid sources.Experiment 2 Partial replacement of fish oil by beef tallow improved antioxidant capacity and innate immunity of red swamp crayfish,Procambarus clarkiiStudies in fish and crabs have shown that the complete replacement of fish oil(FO)with beef tallow(BT)did not affect growth,but impairing antioxidant and immune abilities.In this study,the objective was to investigate the effects of FO,BT and the mixture of FO and BT(FB,1:1)on how these lipid sources modulate growth,antioxidant capacity and immune response of crayfish.For that purpose,three experimental dietaries were formulated to contain FO,BT and FB.After 8 weeks,crayfish exhibited no significant difference in growth and body proximate composition.Crayfish fed BT diets obtained higher hemolymph glucose(Glu),triglyceride(TG)and free fatty acid(FFA)contents.For antioxidant index,crayfish received FB supplemented diets showed higher levels of catalase(CAT)and reduced glutathione(GSH),but lower levels of malondialdehyde(MDA).Furthermore,immunological parameters such as the contents of acid phosphatase(ACP),lysozyme(LZM)and total protein(TP)were increased in crayfish fed FO or FB diets,and the expressions of nuclear factor kappa beta(NF-κB)in tissues were up-regulated by BT while FO was on the contrary.Taken together,the complete replacement of FO with BT may be detrimental to the health of crayfish.In future research,we suggest that BT should be given a reasonable utilization in the feed formulations of crayfish.Experiment 3 Resveratrol reduces lipid deposition and promotes lipid transfer in hepatopancreas of red swamp crayfish,Procambarus clarkiiThe purpose of this experiment was to investigate the effects of different resveratrol concentrations on crayfish growth,lipid deposition,antioxidant ability,and apoptosis under different lipid levels.We set a 2×3 factorial design with two lipid levels(8%and 12%)and three resveratrol concentrations(0%,0.1%,and 0.5%),six experimental diets were prepared and crayfish were fed for 8 weeks.The results indicated that increasing lipid levels is not conducive to the survival of crayfish,while the addition of resveratrol did not affect the growth of crayfish,and significantly reduced the hepatopancreas index and lipid content,and increased muscle yield and crude protein content;In terms of lipid deposition and antioxidant ability,12%lipid obviously increased hemolymph glucose(GLU)and free fatty acid(FFA)concentrations,while glutathione peroxidase(GPx)and reduced glutathione(GSH)contents in hepatopancreas were decreased,and resveratrol supplementation improved this phenomenon;In addition,we also found the addition of resveratrol in the diet could improve the decline of mitochondrial membrane potential(MMP),increase of apoptosis and damage of hepatopancreas caused by 12%lipid.In summary,resveratrol could improve lipid deposition,oxidative stress,and apoptosis when dietary lipid level was increased,and to some degree,it accelerated the yield of crayfish edible part(mainly tail muscle).According to above results,with respect to growth,lipid synthesis and transport,BT could be used as a more suitable alternative to FO.However,considering the antioxidant and immune regulation,complete replacement was not good for health and partial replacement is recommended.Besides,we found when dietary lipid levels were elevated,resveratrol supplementation could improve lipid deposition and increase the proportion of edible portions of crayfish.