Studies About The Utilization Of Dietary Phospholipid Of The Early Juvenile Mud Crab,Scylla Paramamosain

Mud crab(Scylla paramamosain)is an important marine economic crab,which is widely cultured in southeastern coastal areas of China,but the research on its nutritional requirements is still imperfect.There is a lack of high-quality artificial diets for mud crabs,so the aquaculture of this crab still relies on fresh feed.Phospholipids and cholesterol are essential nutrients for crustaceans and play an important role in growth and development.In this paper,the objectives were to evaluate the effects of different phospholipids levels and interaction with cholesterol supplementation on growth,body composition,lipid metabolism,osmotic regulation and antioxidant capacity of early juvenile S.paramamosain,which provides a reference for the development of artificial diets for the mud crab.1.Effects of dietary phosphatidylcholine levels on growth,body composition,osmotic regulation,and antioxidant capacity of early juvenile S.paramamosain.Six groups containing five levels of phosphatidylcholine(PC)and one level of soy phospholipid(SL),respectively,were designed(PC0.1,PC0.5,PC1.0,PC2.0,PC4.0,SL2.0),with three replicates(24 crabs per replicate).A feeding experiment was conducted for 60 days on early juvenile crab with an initial body weight of 8.69 mg.The experimental results showed that the highest weight gain rate(WG)and specific growth rate(SGR)were obtained in the PC2.0and SL2.0 groups.The crude lipid level of whole crabs increased significantly with the increase of dietary PC level.In addition,long-chain polyunsaturated fatty acids(LC-PUFA)of whole body increased significantly with the rise of dietary PC level.Superoxide dismutase(SOD)and catalase(CAT)activities as well as total antioxidant capacity(T-AOC)were significantly increased and malondialdehyde(MDA)content was significantly decreased in the group fed diets with high PC levels compared to the group fed diets with PC0.1 levels.The expression of sterol regulatory element binding protein(srebp-1),fatty acid synthase(fas),fatty acid desaturase 6(Δ6 fad),fatty acid desaturase 9(Δ9 fad),fatty acid elongase 4(elovl4),and fatty acid elongase 6(elovl6)genes decreased gradually with increasing dietary PC levels.However,fatty acid binding protein(fabp)gene expression first increased and then decreased with dietary PC addition.In addition,the highest Na~+/K~+-ATPase(NKA)activity was found in PC4.0 group crabs.nka and Na~+/K~+/2Cl~-cotransporter(nkcc)gene expression also increased with the addition of dietary PC levels.At the end of the experiment,the osmotic regulation ability of the early juvenile crab was evaluated by acute salinity challenge experiment.It was found that the highest survival rate was obtained in the PC4.0group after 10 h of acute salinity stimulation.This indicates that high levels of PC can improve the osmolarity regulation of early juvenile S.paramamosain.2.Effects of dietary different phospholipid and cholesterol levels on the growth,body composition,lipid metabolism,and antioxidant capacity of early juvenile S.paramamosain.Using a two-factor experimental approach,a 2*3 experiment was designed and included two cholesterol levels(0.4%and 0.8%)and three phospholipid levels(1.8%,2.5%,and 3.2%)for a total of six experimental feed groups:CL-PL(cholesterol 0.4%and phospholipid 1.8%),CL-PM(cholesterol 0.4%and phospholipid 2.5%),CL-PH(cholesterol 0.4%and phospholipids 3.2%),CH-PM(cholesterol 0.8%and phospholipids 1.8%),CH-PM(cholesterol 0.8%and phospholipids 2.5%),and CH-PH(cholesterol 0.8%and phospholipids 3.2%),with three replicates(28 crabs per replicate).A feeding experiment was conducted for 8 weeks on early juvenile crab with an initial body weight of 0.01 g.The experimental results showed that in the 0.4%cholesterol group,the finally body weight(FBW),WG and SGR of crabs were significantly higher with the increase of dietary phospholipid level.In the 0.8%cholesterol group,the dietary phospholipid level did not affect the growth of crabs.In addition,in the 1.8%phospholipid group,high cholesterol addition significantly increased the growth of crabs;however,in the 3.2%phospholipid group,high cholesterol addition inhibited the growth of crabs.In the present study,the experimental treatments barely affected the body composition of crabs.In addition,a trend of increasing LC-PUFA with increasing dietary phospholipid levels was observed in all groups with different cholesterol levels.In the 0.8%cholesterol group,MDA levels in crabs tissues increased significantly with the increase in dietary phospholipid levels,accompanied by a significant decrease in CAT activity.In the 0.4%cholesterol group,the expression of lipid synthesis genes srebp-1 and fas increased significantly with the increase of dietary phospholipid level.In the 0.8%cholesterol group,the expression levels of the lipid transport-related genes fabp significantly decreased with increasing dietary phospholipid levels.In addition,the expression levels of LC-PUFA synthesis-related genes elovl4,elovl6,andΔ9fad were significantly increased in the 0.4%cholesterol group with increasing dietary phospholipid levels.On the other hand,at all phospholipid levels,0.8%cholesterol level increased the expression of elovl4,elovl6,andΔ9 fad genes compared to the 0.4%cholesterol group.In summary,under the conditions of the experiment 1,a second-order polynomial regression analysis based on WG concluded that the appropriate level of PC addition to the diet of early juvenile S.paramosain was 2.60%.And the experiment 2 found that increasing dietary phospholipid levels significantly improved the growth performance of early juvenile S.paramosain in the presence of cholesterol deficiency.However,when dietary cholesterol levels were sufficient to meet the growth requirements,3.2%phospholipid addition inhibited the growth and antioxidant capacity of S.paramamosain.In addition,the lipid metabolism of S.paramamosain was influenced by both cholesterol and phospholipids,and there was an interaction between the two nutrients.