Lipids Metabolism And Nutritional Regulation Of α-lipoic Acid In Litopenaeus Vannamei Under Low Salinity Stress

The Pacific white shrimp,Litopenaeus vannamei,can tolerate the low salinity(<5‰)through the various mechanisms of osmotic regulation.But in the aspect of lipidomics,little is known on its strategies to cope with low salinity fluctuations.In the process of low salinity culture,there are various problems,such as slowed down growth rate,higher mortality and lower stress resistance,which was greatly restricted the sustainable development of desalination culture of L.vannamei.In this paper,the regulation of lipid metabolism in L.vannamei under low salinity stress was studied by the technologies of lipidomics,nutrition physiology and biochemistry.Furthermore,the role of lipoic acid in alleviating effect of L.vannamei under low salinity stress was further elucidated by means of nutrition regulation.The mains contents and findings of this paper are as follows:In this study,L.vannamei were grown in two different salinities [3 and 30‰(control)] for 8 weeks,and then a liquid chromatography(LC)–mass spectrometry(MS)-based lipidomics analysis was performed to reveal the lipid profile differences in gill and muscle.L.vannamei at 30‰ salinity had higher weight gain and condition factor than the shrimp under low salinity.Regardless of two salinities,phosphatidylcholine(PC),phosphatidylinositol(PI),phosphatidic acid(PA),phosphatidylethanolamine(PE),and triglyceride(TG)were the main lipids in both shrimp gill and muscle.Compared with the control shrimp at salinity 30‰,the percentage of PC significantly reduced,but TG,PA and PI significantly increased in gill of shrimp at salinity 3‰.It was suggested that the rapid changes of lipids in gill might be an important physiological strategy for L.vannamei to cope with low salinity stress.Lipoic acid,as a new type of feed additive,can change the health states of the organisms by regulating its lipid metabolism.In this study,α-lipoic acid was selected as feed additive to explore its mechanism of alleviating low salinity stress of L.vannamei.Five treatments were set up: the control group with 25% salinity and 0 g/kg α-lipoic acid feed,and the experimental group with 3 ‰ salinity fed with 0(control),0.3,0.6 and 1.2 g/kg α-lipoic acid feed.The results showed that under 3 ‰ salinity stress,the survival rate of L.vannamei was significantly reduced and the feed coefficient was significantly increased.Moreover,the intestinal walls of these shrimps were vacuolated,the lumens of their hepatopancreas were deformed or enlarged,the organs were damaged by oxidation,the compositions of intestinal flora were changed and lastly the diversity was reduced when compared to 25% salinity group.The addition of 1.2 g/kg α-lipoic acid to the diet could significantly improve the growth performance which included survival rate,fatness and feed coefficient,and antioxidant capacity such as MDA content and total antioxidant capacity under low salinity.Furthermore,the vacuole of intestinal wall disappeared,the intestinal wall thinned and the hepatopancreatic lumen returned to tetragonal or cross shape after adding 1.2 g/kg α-lipoic acid,which showed that it could repair the hepatopancreas and intestine to a certain extent,and then significantly improve the abundance and diversity of intestinal flora.Therefore,adding 1.2g/kg α-lipoic acid can effectively alleviate the negative effects of low salinity stress on L.vannamei.