| Six experimental diets were formulated to contain two lipid(10%and 15%)and three taurine(0,1%and 2%)levels using taurine-free casein and gelatin(4:1)as protein sources and fish oil,soybean oil,soybean lecithin as fat sources.A total of 450 juvenile groupers with an initial body weight of 36.3 g were allocated to six groups with triplicate tanks for each group,at a stock density of 25 fish per tank.Fish were hand-fed the diets twice a day during a period of eight weeks.The results are shown as follows:1.Growth performance and tissue composition:Weight gain rate(WGR),specific growth rate(SGR),feed efficiency(FE),and hepatopancrea somatic index(HSI)are affected by taurine level,but not affected by the lipid level.For the 10%lipid group,dietary 1%and 2%taurine significantly improved WGR,SGR,FE,and FI,increased muscular lipid and whole-body crude protein contents vs.the control(P<0.05),while whole-body crude lipid and liver lipid contents were significantly lower than that of control(P<0.05).In the 15%lipid group,the WGR SGR,FE,whole-body ash and crude protein contents increased first and then decreased with increasing taurine level,and reached a peak at dietary 1%taurine,while the change of whole-body,muscular and liver lipid contents were the opposite of whole-body crude protein,and touched the bottom at the dietary 1%taurine(P<0.05).Compared with 10%lipid-fed group,the whole-body,liver and muscular lipid contents were increased(P<0.05),while the whole-body moisture and ash contents were decreased in the 15%lipid-fed group(P<0.05).The above results showed that dietary 1%taurine could promote the growth and protein deposition,but reduce whole-body and tissue lipid deposition of grouper.However,dietary excessive taurine(2%)caused restricted growth.The side-effect of 10%lipid fed group was more significantly enhanced by the 15%lipid-fed group.2.Plasma and liver biochemical components:Compared with the 10%lipid-fed group,the 15%lipid group had higher levels of HDL-C,LDL-C,TG,TC,VLDL,apolipoprotein(Apo-B),insulin(INS)and leptin(LEP)(P<0.05).However,the levels of insulin growth factor(IGF-1),HMG-CoA reductase(HMGR),cholesterol 7a hydroxylase(CYP7A1)and adiponectin(ADPN)were not affected by dietary lipid levels(P>0.05).At 10%lipid level,dietary 1%taurine increased the levels of HDL-C,LEP,CYP7A1,TG,VLDL and total bile acid(TBA),while reduced LDL-C and Apo-B levels(P<0.05)compared with 0%and/or 2%taurine group.However,TG and ADPN levels were not affected by dietary taurine levels(P>0.05);At 15%lipid level,levels of LDL-C,TG,Apo-B,HMGR,LEP,and ADPN decreased first and then increased with the increase in dietary taurine level,and the values were lower than the control(P<0.05).The levels of INS and CYP7A1 showed an opposite trend.The dietary addition of taurine could affect the enzyme activity and plasma hormone levels related to lipid metabolism,promote triglyceride,cholesterol decomposition and transport,and bile acid synthesis.3.Hepatic and muscular lipidomics:A total of 1565 lipid molecules were detected in the liver.These molecules were divided into 30 lipid subclasses.Compared with the 10%lipid-fed group,a total of 22 differential lipid molecules were detected in the liver of 15%lipid-fed group,21 of which were increased,belonging to hemolytic phosphatidylethanolamine(LPE),phosphatidylcholine(PC)and phosphatidylethanolamine(PE);only one differential lipid molecule was decreased,which belonged to TG.At 10%lipid level,the dietary addition of taurine caused a change of a total of 34 liver differential lipid molecules.The decreased differential lipid molecules were mainly TGs,while the increased differential lipid molecules were mainly PEs and PCs;At 15%lipid level,the dietary addition of taurine caused a change of a total of 131 differential lipid molecules in the liver,38 of which were increased molecules including 14 PC species,9 PE species,3 PG,and 5 LPE;the other 93 differential lipid molecules were decreased,which belonged to TG species.A total of 1108 lipid molecules were detected in the muscle,and were divided into 22 lipid subclasses.Compared with the 10%lipid-fed group,a total of 12 differential lipid molecules(3 PS,5 PC,and 3 TG species)were detected in the 15%lipid-fed group.PS(18:0/18:2),PC(32:2),and PS(37:3)were decreased in the 15%lipid-diet group,and the rest were increased vs.10%lipid-fed group.Dietary addition of taurine to the 10%lipid-fed group had little effect on muscular lipid molecules.But the dietary addition of taurine to 15%lipid-fed group caused a change of 14 differential lipid molecules,including 4 PE,2 PS,5 PC,and one PI,one MGDG,and one TG species.Among them,PC(36:4p)and TG(14:0/17:1/18:2)were decreased by dietary taurine addition.The above results indicated that a more pronounced response of differential lipid molecules to dietary taurine level in the liver than in the muscle.It is speculated that taurine may regulate lipolysis and metabolism by increase glycerophospholipid and sphingolipid components,and decreased glyceride components in the liver.4.Bile acid spectrum:A total of 30 kinds of bile acids were detected in the bile of grouper,of which taurocholic acid(TCA),taurochenodeoxycholic acid(TCDCA),taurodeoxycholic acid(TDCA)are the three most abundant bile acids,accounting for 60%,25%,and 5%of total bile acids,respectively.Dietary taurine addition at any lipid level resulted in increased contents of bile cholic acid(CA),chenodeoxycholic acid(CDCA),TCA,TCDCA,TDCA,and tauroursodeoxycholic acid(TUDCA),and reduced contents of deoxygenation Cholic acid(DCA),ursodeoxycholic acid(UDCA),taurocholic acid(TLCA),w-muricholic acid(w-MCA),r-muricholic acid(r-MCA),tauromuricholic acid(TMCA),taurohyomuricholic acid(THCA),AlloCA(Allolithocholic acid),and glycine conjugated cholic acid.However,glucolithocholic acid(GLCA),lithocholic acid(LCA),7-ketolithocholic acid(7-KLCA),12-KLCA(12-ketolithocholic acid),7-ketodeoxycholic acid(7-KDCA)and IsoLCA(Isolithocholic acid)were not affected by dietary taurine levels.The above results indicated that dietary taurine addition could regulate bile acid metabolism by changing the bile acid spectrum to maintain the homeostasis of lipid metabolism in the fish species. |
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