Study On Nutritional Physiology Of Phosphorus In Juvenile Chinese Mitten Crab(Eriocheir Sinensis)

Phosphorus（P）,macro-mineral element,is a necessary for the growth of aquatic animals.Due to the low absorption rate of P from water,it seems no doubt that aquatic animals must obtain most of P from their diets.Inadequate P intake could decrease growth performance,increase body lipid content,reduce calcium（Ca）,P deposition and bone mineralization of aquatic animals.However,excessive P would cause eutrophication of water as P is one of the main limiting nutrients of eutrophication in the freshwater ecosystem.Therefore,appropriate dietary P is very important for sustainable aquaculture.Meanwhile,the sources of inorganic phosphate,the Ca to P ratios in diet,and pH of the intestinal tract of animals would affect the absorption and utilization of P in diet.Thus,this study was aimed to investigate the effects of dietary P,P source,Ca to P ratio and several organic acids on growth,body composition,antioxidant activities and Ca and P metabolism of juvenile Chinese mitten crab（Eriocheir sinensis）.The results can provide scientific basis for the P nutrition requirement,enrich the theoretical data of mineral nutrition,and also provide theoretical reference for the development of high-efficiency and high-quality formula feed for juvenile E.sinensis.1.Effects of dietary phosphorus on growth performance,body composition,antioxidant activities and lipid metabolism of juvenile Chinese mitten crab（Eriocheir sinensis）This study investigated the effects of dietary P on growth,body composition,antioxidant activities and lipid metabolism of juvenile Chinese mitten crab.Six diets containing available P levels at 0.20%,0.44%,0.99%,1.37%,1.75%and 2.01%were prepared and fed to juvenile E.sinensis（0.38±0.01 g）for 56 days.The weight gain,specific growth rate and molting frequency were markedly affected by dietary P,and the highest weight gain and specific growth rate were obtained in crabs fed the 0.99%available P diet.With increasing the dietary available P levels,the whole-body ash,Ca,and P contents,as well as the hepatopancreas and serum P contents increased,while the whole-body Mg content decreased.The increase of dietary P levels significantly decreased the lipid contents of whole-body and hepatopancreas,while increased the crude protein content of hepatopancreas.The hepatopancreas and serum alkaline phosphatase activities increased with an increase in dietary available P levels from 0.20%to 1.37%,and then decreased afterward.The crabs fed 1.37%available P diet had a markedly higher alkaline phosphatase activity than those fed 0.20%,0.44%and 2.01%available P diets.Moreover,dietary P significantly affected total antioxidant capacity,the activities of total superoxide dismutase and glutathione peroxidase,and the malondialdehyde content in the hepatopancreas.The highest antioxidant activity and lowest malondialdehyde content in the hepatopancreas were found in the crabs fed 1.37%of available P in the diet.The relative m RNA expression showed that dietary P reduced hepatopancreas lipid accumulation might be produced through suppressing the genes related to lipid synthesis and promoting the genes related to lipid transport.This study demonstrates that optimum dietary P could enhance growth,antioxidant capacity and reduce hepatopancreatic lipid accumulation in juvenile E.sinensis and the range of available P in the diet is suggested to be 1.16%–1.51%.2 Effects of dietary calcium to phosphorus ratios on growth,body composition,antioxidant capacity,osmotic pressure regulation and calcium and phosphorus metabolism of juvenile Chinese mitten crab（Eriocheir sinensis）.The study evaluated the effects of dietary Ca to P ratios on growth,body composition,antioxidant capacity,osmotic pressure regulation and Ca and P metabolism of juvenile Chinese mitten crab.Six isonitrogenous and isolipidic diets with Ca levels of 0.5%（low-Ca）,1.5%（mid-Ca）and 2.5%（high-Ca）and total P levels of 1.5%and 2.0%were prepared by using Na H₂PO₄·2H₂O as P source and Ca Cl₂ as Ca source.The crabs with initial weight of 4.39±0.01 g were fed diets for 56 days.When the dietary P level was 1.5%,the weight gain,specific growth rate and molting frequency in mid-Ca group were significantly higher than those in low-Ca group.When the dietary P level was 2.0%,the final weight,weight gain rate,specific growth rate and molting frequency in mid-Ca and high-Ca groups were significantly higher than those in low-Ca group.Regardless of dietary P levels,dietary 2.5%Ca could significantly increase the whole-body ash content,the whole-body and hepatopancreas Ca and P contents,and serum P content,while the whole-body crude lipid content decreased compared with dietary 0.5%Ca.Dietary 1.5%Ca significantly increased the gene expressions related to the absorption of Ca and P compared with 0.5%Ca regardless of dietary P levels.The serum AKP activity and osmotic pressure,and gill Na⁺K⁺-ATPase activity and NKA gene expression in the mid-Ca and high-Ca groups were higher than those in the low-Ca group at the same dietary P level.When dietary P was 1.5%or 2.0%,dietary 1.5%Ca could significantly reduce the malondialdehyde content and increase the activities of total antioxidant capacity and total superoxide dismutase in hepatopancreas.Taken together,the appropriate ratio of dietary Ca to P was 0.76-1（the actual dietary Ca/P level was 1.59/2.10～1.58/1.59）,which can promote growth,improve the absorption and deposition of calcium and phosphorus,and enhance the ability of osmoregulation and antioxidation of juvenile E.sinensis.3 Effects of dietary organic acids on growth,antioxidant activities,immunity,and calcium and phosphorus metabolism of juvenile Chinese mitten crab（Eriocheir sinensis）.The present study aimed to determine the effects of citric,malic,α-ketoglutaric,fumaric,and lactic acid on growth,antioxidant activities,immunity,and Ca and P metabolism of juvenile E.sinensis.A control experimental diet（C）was formulated and supplemented with 0.2%citric acid（CA）,malic acid（MA）,α-ketoglutaric acid（AKG）,fumaric acid（FA）and lactic acid（LA）to feed juvenile E.sinensis（initial body weight3.09±0.01 g）.After 56 days,the CA,AKG and FA groups had markedly higher final body weight,weight gain,and specific growth rate than the C group,and the highest values were found in the AKG group.The feed conversion ratio in the CA and AKG groups was lower than that in the C group.The CA,AKG and FA groups had lower crude lipid content,and higher Ca and P contents in the whole-body.Meanwhile,dietary CA,AKG and FA enhanced the genes expressions related to the absorption of Ca and P,and the dietary available P than the C group.Dietary organic acids significantly increased the whole-body crude ash content,the Ca and P contents in the hepatopancreas,muscle and serum.The CA,AKG and FA groups had higher hepatopancreatic antioxidant enzyme activities and lower malondialdehyde content in the hepatopancreas than those in the C group.The alkaline phosphatase activities in the serum and intestine,the acid phosphatase activity in the intestine and total protein content in the serum significantly increased in the organic acids-supplementation groups.The acid phosphatase activity in the serum in the AKG group was significantly higher than that in the C group.Dietary CA,AKG and FA significantly increased the digestive enzyme activities（trypsin,lipase and amylase）in the hepatopancreas and intestine.This study indicates that dietary CA,AKG and FA could improve growth performance,antioxidant capacity,non-specific immunity,digestive enzyme activities,and the absorption and deposition of Ca and P of juvenile E.Sinensis.The CA,AKG and FA have good application prospects as feed additives for E.sinensis.4 Effects of dietary phosphorus sources and citric acid on growth,body composition,anti-oxidation activity,and calcium and phosphorus metabolism of juvenile Chinese mitten crab（Eriocheir sinensis）.The study aimed to investigate the effects of different sources of inorganic phosphate,dicalcium phosphate（DCP）,monocalcium phosphate（MCP）and mono-calcium and di-calcium phosphate（MDCP）at two citric acid（CA）levels（0%and 0.2%）on growth,body composition,anti-oxidation activity,and Ca and P metabolism of juvenile E.sinensis.Six isolipidic and isonitrogenous diets were fed to juvenile E.sinensis（4.11±0.02 g）for 8 weeks.The results showed that there was no significant difference on growth of crabs among the groups.The crude lipid content of the whole-body in the MDCP group was significantly lower than that in the DCP group when the crabs fed diets without the addition of CA.At the same dietary CA level,the whole-body crude ash content,the whole-body and hepatopancreas Ca and P content,and dietary available P content in the MCP and MDCP groups were significantly higher than those in the DCP group.Dietary CA could significantly increase the whole-body crude ash content,the whole-body and hepatopancreas Ca and P content,and dietary available P content in the MCP and MDCP groups.At the same dietary CA level,the serum P content and the gene expressions related to the absorption of P and Ca in the MDCP group were markedly higher than those in the DCP group.Meanwhile,dietary citric acid could significantly increase the gene expression of calreticulin.At the same dietary CA level,the activities of total antioxidant capacity and total superoxide dismutase in the hepatopancreas in MDCP group was significantly higher,while the malondialdehyde content significantly lower than those in the DCP group.Dietary CA could significantly increase the activities of total antioxidant capacity and total superoxide dismutase in the hepatopancreas in the DCP,MCP and MDCP groups.This study indicates that CA could improve the Ca and P deposition and antioxidant capacity of crab fed with MCP and MDCP,which indicated that CA could be widely used in the diets of crabs.In addition,the MCP and MDCP have similar effects on antioxidant capacity and Ca and P deposition.Simultaneously,as an emerging P source,the cost of MDCP is lower than MCP.Take all factors into account,MDCP is the most suitable P source for juvenile E.sinensis.