Study On Optimum Requirement For Phosphorus And The Relative Biological Value Of High Soluble Monodicalcium Phosphate In Diet Of Largemouth Bass(Micropterus Salmoides)

In this experiment,different levels of Monocalcium phosphate(MCP)and Mono-dicalcium phosphate with high solubility(MDCP)were added to low-phosphorus basal diets to study the effects of growth performance,apparent digestibility coefficient of phosphorus(ADCp)and nitrogen(ADCn),produced phosphate value(PRR),produced nitrogen value(PNRR),phosphorus contents of vertebra and body,ash contents of body were determined to compare the biological value of MDCP relative to MCP,and the dietary phosphorus requirement of largemouth bass were studied as well.Through the study of bile acid synthesis genes and lipid metabolism related genes,determine the effect of phosphorus(P)on lipid metabolism of largemouth bass1.Study on the optimum requirement of phosphorus and the effect of phosphorus on lipid metabolism for largemouth bass: Based on the P0 with basal P content of 6.6g/kg,8.86,11.08,13.29,15.51g/kg MCP were added to equally supply 2.0,2.5,3.0,3.5 g/kg of phosphorus,respectively.The four diets were named as P2.0,P2.5,P3.0,P3.5.Each diet was fed to four replicates with 40 largemouth bass(8.5±0.1g)in each tank for 8w.Weight gain rate(WGR)and retention of P and N were significantly increased with optimum level of MCP inclusion in fish diet.Based on the WGR and P retention,the requirement of dietary available P for largemouth bass was 0.51% with the regression models.Low phosphorus diet had no effect on the liver tissue of largemouth bass,and the liver tissue was generally normal.However,in the case of phosphorus deficiency in feed,the plasma P level of largemouth bass was reduced.The analysis of the mRNA relative expression of lipid metabolism-related genes showed that the inclusion of P could increase the cholesterol transport to the liver by up-regulating the APOA1 and also up-regulate the CYP7A1 to improve the bile acids synthesis and cholesterol metabolism.Besides,optimal dietary P level also increased the CPT1 gene expression to regulate the fatty acid beta oxidation process and promote the energy metabolism of fish.2.Study on the biological value of highly water-soluble MDCP relative to MCP: Based on the P0 8.86,11.08,13.29,15.51 g/kg of MCP,and 9.34,11.67,14.01,16.34 g/kg of MDCP were added to equally supply 2.0,2.5,3.0 and 3.5 g/kg of phosphorus,respectively.The nine experimental diets were accordingly named P0,P2,P2.5,P3.0,P3.5 and DP2.0,DP2.5,DP3.0,DP3.5.Each diet was fed to four replicates with 40 largemouth bass(8.5±0.1g)in each tank for 8w.Higher weight gain rate(WGR),ADCp,PRR and whole body ash content of the largemouth bass was observed with increasing levels of dietary MCP and MDCP,but there was no significant difference between the two phosphorus sources(P>0.05).With the increase of MDCP,the WGR and ADCp were continually enhanced(P<0.05).The PRR were increased and then declined,and the lowest and highest values were observed in P0 and DP3 group,respectively(P<0.05).The relative biological value of MDCP relative to MCP was 100% and 118% based on the WGR and PRR through slope method.