The Effect Of Dietary Calcium And Phosphoruslevels On Growth Performance,Digestibility,Absorption And Deposition Of Calcium And Phosphorus On Lateolabrax Maculatus

A feeding trial was conducted to investigate the effect of dietary calcium?Ca?and phosphorus?P?levels on growth performance,digestibility,absorbption and of calcium and phosphorus on Lateolabrax maculatus in reared freshwater.In this study,de-boned fishmeal and casein as the protein source.The juvenile L.maculatus?mean initial weight 7.24±0.02 g?were fed nine isonitrogenus and isolipidic diets,containing three graded levels of Ca derived from calcium chloride correspond to three levels of P derived from sodium dihydrogen phosphate and dipotassium phosphate for 56 days.The contents of total Ca and P?Ca%/P%?in each diet were0.40/0.40,0.40/0.75,0.40/1.50,0.75/0.40,0.75/0.75,0.75/1.50,1.50/0.40,1.50/0.75,1.50/1.50,respectively.Five hundred forty fish were assigned to nine treatments consist of triplicate groups with 20 fish each.Samples were collected at 21 days and 56 days,respectively.The main results were as follows:1.The effect of dietary Ca and P levels on growth performance and osmotic pressure regulation of L.maculatusAfter feeding test diets for 21 days,the results showed that SR,WG,SGR,FE and PER in fish fed 1.50/0.40 and 0.75/0.40 Ca/P diets were significantly lower than other groups?P?27?0.05?.Two-way ANOVA analysis indicated that WG,SGR,SR,FR,VFR and CF significantly decreased with dietary Ca supplementation?P?27?0.05?,and WG,SGR,SR,PER,FE,FR and CF significantly increased with dietary P supplementation?P?27?0.05?.After feeding test diets for 56days,the results showed that the SR in fish fed 1.50/0.40 and 0.75/0.40 Ca/P diets was 0%.In addition,the SR,WG,SGR,FE and PER in fish fed 0.40/0.40 and 1.50/0.75 Ca/P diets were significantly lower than other groups?P?27?0.05?,and there was no significant difference among other groups?P?29?0.05?.The maximum values of WG,SGR,FE and FR appeared in fish fed0.40/1.50 diet.Two-way ANOVA analysis indicated that the WG,SGR,FE,PER and SR significantly declined in fish fed 1.50%Ca diets?P?27?0.05?.At the same dietary Ca level,WG,SGR and FR of L.maculates gradually raised with increasing dietary P levels?P?27?0.05?,but HSI,VSI and VFY gradually declined?P?27?0.05?.In conclusion,suitable Ca/P ratio of L.maculatus was 1:3.75?0.40/1.50?.After feeding juenvile L.maculatus for 21 days,the results showed that dietary phosphorus levels significantly influenced serum AKP and TRACP activities and Na⁺K⁺-ATPase activitiy of gill?P?27?0.05?,and serum AKP,TRACP and gill Na⁺K⁺-ATPase activities in fish fed 1.50%P diets were significantly higher than fish fed 0.40%P diets?P?27?0.05?,while serum TRACP activity showed an opposite trend.Dietary Ca levels significantly influenced serum TRACP activity and Ca²⁺-ATPase activity of gill?P?27?0.05?.Serum TRACP activity in fish fed 1.50%Ca diets was significantly lower than fish fed 0.40%Ca and 0.75%Ca diets?P?27?0.05?,while Ca²⁺-ATPase activity of gill on the contrary.After feeding test diets for 56 days,the results showed that serum AKP activity increased with increasing dietary Ca and P levels.Moreover,serum AKP activity was significantly higher in fish fed 1.50/1.50 Ca/P diet?P?27?0.05?.However,there was no significantly difference in serum TRACP activity between the groups?P?29?0.05?,and serum osmotic pressure in fish fed 0.40/0.40 Ca/P diet was significanty lower than other groups?P?27?0.05?.Ca²⁺-ATPase activity of gill in fish fed 1.50%Ca diets was higher than fish fed0.40%Ca diets?P?27?0.05?,while Na⁺K⁺-ATPase activitiy of gill on the contrary.Above this,the osmotic pressure regulation ability in fish fed 0.40/0.40 Ca/P diet was weak and harmful to maintain osmotic pressure balance.2.The effect of dietary Ca and P levels on apparent digestibility and nutrient deposition of L.maculatusApparent digestibility of feed dry matter increased with increasing dietary P levels,and the values in fish fed 0.40/1.50 Ca/P diet was significantly higher than fish fed 0.40/0.40 Ca/P diet?P?27?0.05?.Apparent digestibility of calcium and phosphorus were significantly affected by dietary Ca and P levels?P?27?0.05?.The fish 1.50%Ca diets significantly decreased apparent digestibility of phosphorus and significantly increased apparent digestibility of calcium?P?27?0.05?,and fish fed 1.50%P diets significantly reduced apparent digestibility of calcium and phosphorus?P?27?0.05?.But at the dietary 0.40%Ca level,apparent digestibility of phosphorus in fish fed 0.40%P diet was significantly lower than fish fed 1.50%P diets?P?27?0.05?.The whole-body crude protein content significantly decreased with the increase of dietary Ca levels,and the values in fish fed 1.50/1.50 Ca/P diet was significantly lower than other groups?P?27?0.05?.The whole-body crude lipid content declined with the increasing dietary P levels,and the values in fish fed 0.40/0.40 Ca/P diet was significantly higher than other groups?P?27?0.05?.The whole-body crude ash content improved significantly with the increase of dietary Ca and P levels?P?27?0.05?,and whole-body Ca and P contents also increased as the dietary P supplementation.The deposition rate of feed dry matter and protein in fish fed 0.40/0.40 Ca/P diet was significantly lower than other groups?P?27?0.05?.With the increase of dietary Ca levels,the deposition rate of feed dry matter,protein,lipid and Ca significantly declined?P?27?0.05?,and the deposition rate of P gradually decreased.With the increase of dietary P levels,the deposition rate of feed Ca significantly increased?P?27?0.05?,while the deposition rate of ash and P significantly decreased?P?27?0.05?.Above of this,the results showed that dietary Ca and P levels significantly affected apparent digestibility of feed Ca,P and nutrient deposition.3.The effect of dietary Ca and P levels on absorption and excretion of Ca and P of L.maculatusIn gill,dietary 0.40/0.40 and 0.40/0.75 Ca/P level significantly enhanced the expression of PTHrP,VDR and NCX genes than fish fed 1.50/1.50 Ca/P diet?P?27?0.05?.Moreover,the genes expression in fish fed 0.40/0.40 Ca/P diet was significantly higher than fish fed 1.50/1.50 Ca/P diet?P?27?0.05?,which promoted the absorption of Ca.In intestine,the trend of NCX gene expression affected by dietary Ca and P levels was consistent with the PTHrP and VDR genes expression.Moreover,the genes expression in fish fed 0.40%Ca diets were significantly higher than fish fed 1.50%Ca diets?P?27?0.05?,and the genes expression showed an elevated tendency with increase of dietary P levels.The expression of NaPiIIa and PiT1 genes in fish fed 0.40%Ca diets were significantly higher than fish fed 1.50%Ca diets?P?27?0.05?,and the expression of NaPiIIb gene in fish fed 0.75%P diets than fish fed 0.40%P and 1.50%P diets?P?27?0.05?,but the expression of PiT2 gene was significantly upregulated in fish fed 0.75/1.50 and 1.50/0.75 Ca/P diets?P?27?0.05?.In kidney,the expression of NaPiIIa and PTHrP genes in fish fed 0.40/0.40 Ca/P diet were significantly lower than fish fed 1.50/1.50 Ca/P diet?P?27?0.05?,while the expression of NCX gene was significantly higher than fish fed 1.50/1.50 Ca/P diet?P?27?0.05?.However,the trend of FGF23 gene expression was opposite to NaPiIIa gene.In conclusion,the results indicated that dietary Ca levels changed the expression of NCX gene and therefore regulated the absorption of Ca by affecting the expression of PTHrP and VDR genes in gill and intestine.and dietary Ca and P levels significantly influenced the expression of NaPiIIa,NaPiIIb,PiT1 and PiT2 genes to regulate the absorption of P in intestine.But the expressin of NaPiIIa gene was negative feedback by FGF23 to regulate the reabsorption of P in kidney.