The Effects Of Dietary Calcium And Phosphorus Levels On The Absorption And Deposition Of Calcium And Phosphorus Of Lateolabrax Japonicus Reared In Freshwater

A study was conducted to investigate the effects of dietary calcium?Ca?,phosphorus?P?and their interaction between Ca and P on the absorption and deposition of Ca and P in Lateolabrax japonicus?L.japonicus?reared in freshwater.Six isonitrogenous and isoenergetic semi-purified diets,containing two graded levels of Ca derived from calcium carbonate for each of three levels of P derived from sodium-?potassium-?dihydrogen phosphate,were fed to juvenile L.japonicus.The contents of total Ca and total P?Ca% /P%?in each diets were 0.30 /0.40;0.30 /0.80;0.30 /1.50;3.00 /0.40;3.00 /0.80;3.00 /1.60.Prior to the experiment,450 juvenile L.japonicus with an initial weight of 1.8±0.02 g were distributed to six treatments equally.After 10 weeks,the results showed that:1.Effect of dietary Ca and P levels on growth and body composition of L.japonicus.L.japonicus fed diet contained 3.0% Ca and 0.4% P had the lowest survival?P<0.05?,and the survival in other groups were not significantly different?P>0.05?.The lowest and highest values of weight gain?WG?or specific growth rate?SGR?appeared on the groups of 3.0% Ca + 0.4% P and 0.3% Ca + 0.8% P,respectively.The moisture,protein and lipid in whole-body and the moisture in muscle were not significantly different?P>0.05?.The muscle crude protein and crude lipid of L.japonicus fed diet without Ca supplementation significantly reduced with dietary P supplementation,while crude ash in whole-body showed opposite phenomenon?P<0.05?.And crude ash in muscle of L.japonicus fed dietary 3.0% Ca showed significantly higher levels than that in dietary-Ca-free groups?P<0.05?.The two-way ANOVA indicated that dietary P could significantly affect WG,SGR,survival,feed efficiency?FE?,feeding rate?FR?,protein efficiency ratio?PER?,crude ash in whole-body and crude protein in muscle?P<0.05?.And dietary Ca could significantly affect crude lipid and crude ash in muscle?P<0.05?.The WG,SGR,survival,FE,FR,PER and crude protein in whole-body were significantly affected by the interaction of dietary Ca and P?P<0.05?.According to the results of growth,when the dietary Ca was 0.3%,the optimum Ca/P was 0.38,while the dietary Ca derived from calcium carbonate reached to 3.0%,the optimum Ca/P was 3.80.2.Effect of dietary Ca and P levels on absorption and excretion of Ca and P of L.japonicus.Serum Ca and P concentration were influenced significantly by dietary Ca levels?P<0.05?.In the intestine,the sodium-dependent phosphate transporter 2 isoform X1?Na-Pi ?1?,parathyroid hormone-related peptide receptor?PTHrPR?and vitamin D receptor b?VDR b?mRNAs were upregulated and the activity of Ca²⁺-ATPase was improved with increasing dietary P levels?P<0.05?.When P was limited in diets,the intestinal sodium/calcium exchanger 2-like isoform X1?NCX ?1?and VDR b mRNAs were downregulated significantly in the group of 3.0% Ca comparing with diet-Ca-free groups?P<0.05?.While dietary P was 0.8%,intestinal NCX ?1 and PTHrPR mRNAs were upregulated significantly in the group of 3.0% Ca comparing with diet-Cafree group?P<0.05?.Branchial Na-Pi ?1 and VDR b mRNAs in each group were not significantly different?P>0.05?.When dietary Ca was not added,L.japonicus fed diets with 1.5% P had significantly lower expression of NCX ?1 and PTHrPR mRNAs than L.japonicus fed diets with 0.8% P?P<0.05?,which was contrary to the group of 3.0% Ca.The renal Na-Pi ?1 mRNAs,under diet-Ca-free groups,were downregulated significantly with increasing dietary P?P<0.05?,but renal fibroblast growth factor 23?FGF23?and PTHrPR mRNAs showed opposite situation.On the contrary,when dietary Ca was 3.0%,renal Na-Pi ?1 and FGF 23 mRNAs were upregulated and downregulated significantly respectively with increasing dietary P?P<0.05?.When dietary P unsupplemented,renal PTHrPR mRNAs were upregulated significantly with dietary high-Ca added comparing with diet-Ca-free groups?P<0.05?,which was not found on the high-P groups.The above results showed that the different dietary Ca and P levels could regulate the absorption and excretion of Ca and P in gill,intestine and kidney with corresponding transporter regulation by VDR b,PTHrPR and FGF 23.3.Effect of dietary Ca and P levels on deposition of Ca and P of L.japonicus.The whole-body Ca and P concentration increased significantly with increasing dietary P under diet-Ca-free groups?P<0.05?,and the vertebra Ca and P concentration increased significantly with increasing dietary Ca and P levels?P<0.05?,however,both whole-body and vertebra Ca/P were not significantly different?P>0.05?.There was positive correlation between opercular Ca/P and dietary Ca?P<0.05?,while the scale Ca/P were significantly affected by the interaction of dietary Ca and P?P<0.05?.When L.japonicus fed diets without Ca and P supplementation,the scales bone morphogenetic protein receptor type-2?BMPR ??and macrophage colony-stimulating factor receptor 2?MCSFR ??m RNAs were downregulated significantly comparing with other groups?P<0.05?.Under the dietary Ca limited situation,vertebra BMPR ? mRNAs of L.japonicus fed diets without P supplementation were downregulated significantly comparing with dietary P supplied groups,however,the expression of vertebra MCSFR ? m RNAs under diet-P-free groups were 3.6 and 4.3 times as much as dietary 0.8% and 1.5% P groups,respectively?P<0.05?.The results indicated that scale was an active tissue to regulate the balance of body mineral.And L.japonicus fed diets with different Ca and P supplementation could regulate the homeostasis of Ca and P through the regulation of BMPR ? and MCSFR ? in scale and vertebra,and the mobilization of Ca and P in scale and opercular.