Effects Of Dietary Phospholipids Sources And Levels On Growth,Body Composition And Antioxidant Capacity Of The Early Juvenile Green Mud Crab,Scylla Paramamosain(Estampador)

Phospholipids,as an important compound lipid,is one of the important nutrients in aquatic animal diet.Aquatic animals generally have a lower demand for phospholipids,but phospholipids play an important role in the growth,development,immunity and reproduction of fish and crustaceans,especially in their early life stages.Experts and scholars have carried out phospholipids nutrition research in many aquatic animals,but there is no report on phospholipids nutrition research of Scylla paramamosain.S.paramamosain is the most important marine cultured crabs in China.However,due to the late start of seedling breeding and the lack of nutrition research,the survival rate and quality of seedlings are low.At present,the culture of S.paramamosain still depends on fresh food.In view of this situation,this paper systematically studies the effects of different phospholipids sources and levels on the growth,survival,body composition,lipid metabolism,antioxidant ability and osmoregulation of early juvenile S.paramamosain,and obtains the diet appropriate phospholipid sources and levels for early juvenile S.paramamosain,which provides a certain theoretical reference for the research and development of artificial pellet diet for S.paramamosain.The main experimental contents include the following two aspects:(1)Four iso-nitrogenous and iso-lipidic diets were designed to investigate the effects of dietary phospholipids(PL)levels(with 0%,1%,2%and 4%soybean lecithin(SL)supplementation)on growth performance,lipid metabolism and antioxidant capacity in early juvenile S.paramamosain.There were three replicates of 28 crabs(initial weight 42.23±0.21mg)for each diet treatment,and growth trial lasted for 8weeks.At the end of growth trial,there was no significant difference in survival among all treatments.Crabs fed diet with 2%SL obtained highest weight gain(WG)than other crabs.Besides,the contents of whole body lipid and long chain highly unsaturated fatty acids(LC-PUFA)significantly increased with elevating dietary SL levels.In the hepatopancreas,crabs fed diet with 0%SL had significantly higher malondialdehyde(MDA)concentration than other crabs.And crabs fed diet with 2%SL obtained significantly higher superoxide dismutase(SOD)activity than crabs fed diets with 0%and 4%SL.Moreover,the mRNA expression of Na~+/K~+-ATPase(NKA)was significantly down-regulated with dietary SL supplementation over 2%.Based on the second order polynomial regression analysis of WG,2.37%dietary SL level was the optimal demand for early juvenile S.paramamosain.Moreover,we found crabs fed diet with 2%SL obtained better antioxidant capacity than other crabs.(2)Present study was designed to evaluate the effects of dietary egg yolk lecithin(EL)supplementation on survival,growth,lipid metabolism and antioxidant capacity of early juvenile S.paramamosain.Total of 420 crabs(initial weight 8.14±0.30mg)were randomly divided into five groups(with 3 replicates)and fed with diets containing different EL levels(with 0%(EL0),1%(EL1),2%(EL2),3%(EL3),and 4%(EL4)EL supplementation)for 8 weeks.The crabs fed diet with 3%EL supplementation obtained highest survival(92.86±4.52%).Significantly higher final body weight(FBW),weight gain(WG),and specific growth rate(SGR)values were also observed in the EL3 group,and there was no significant difference from the EL2 group.The crabs in EL2 group obtained highest molting frequency(MF)and mRNA expression level of ecdysone receptor(EcR)gene.In addition,the whole body lipid content of crabs increased with the increase of dietary EL level.Moreover,crabs fed diet with 2%EL supplementation had significantly higher n-3/n-6 ratio.The highest mRNA expression level of fatty acid-binding protein(FABP)gene also observed in EL2 group.Furthermore,the crabs in EL4 group had significantly lower mRNA expression level of fatty acid synthase(FAS)gene.In hepatopancreas,the concentration of malondialdehyde(MDA)significantly decreased with the increase of dietary EL level.Meanwhile,significantly higher SOD activity was observed in the EL2 and EL3 groups.Based on the second-order polynomial regression analysis of SGR,present study suggested that 2.56%dietary EL level could achieve the maximum growth of early juvenile S.paramamosain.In conclusion,two independent experiments were conducted to investigate the effects of dietary soybean lecithin and egg yolk lecithin on the growth,body composition,lipid metabolism and antioxidant capacity of early juvenile S.paramamosain.The survival,growth and antioxidant ability of early juvenile S.paramamosain were significantly improved by adding appropriate dietary phospholipids.In addition,dietary phospholipids can also affect the lipid metabolism of early juvenile S.paramamosain,and increase the whole body lipid and long-chain polyunsaturated fatty acid levels.Based on the second-order polynomial regression analysis,2.37%-2.56%dietary phospholipids level could achieve the maximum growth of early juvenile S.paramamosain.There was no significant difference between the two phospholipids sources on the early juvenile S.paramamosain,and soybean lecithin was considered to be the more suitable phospholipids source for the early juvenile S.paramamosain.