Effect Of Dietary Iron And Manganese Levels On Growth,mineral Deposition,antioxidant Ability,nonspecific Immunity In Juvenile Swimming Crab(portunus Trituberculatus)

In this study,juvenile swimming crab（Portunus trituberculatus）,an economic marine crab in China,was selected as the experimental object.Different dietary iron（Fe）and manganese（Mn）levels were designed to evaluate the effects of Fe and Mn levels on growth,mineral deposition,antioxidant capacity and non-specific immune capacity,and to determine the optimal dietary Fe and Mn requirements for juvenile swimming crab.The main results are as follows:1.An 8 weeks feeding trial was conducted to determine the optimal Fe requirement for juvenile swimming crab,six isonitrogenous and isolipidic diets were formulated,and the analyzed Fe levels（Fe SO₄·7H₂O as the iron source）were 55.2,75.5,97.7,132.1,218.9 and 373.9 mg/kg,respectively.Each diet had three replicates,and each replicate fed 10 juvenile crabs with an initial body weight of 10.61±0.25g.The results showed that the highest percent weight gain（PWG）and specific growth rate（SGR）were recorded in crabs fed the diet with 218.9 mg/kg Fe（P<0.05）,but dietary Fe levels had no significant difference in survival rate of crabs（P>0.05）.Fe deposition in hepatopancreas and carapace significantly increased with dietary Fe levels increasing from 55.2 to 373.9 mg/kg（P<0.05）,but there was no significant difference in muscle among all groups（P>0.05）.Catalase（CAT）activity in hepatopancreas was significantly increased with increase of dietary iron levels（P<0.05）;crabs fed the diet containing132.1 mg/kg Fe had the highest total antioxidant capacity（T-AOC）activity in hepatopancreas among all treatments（P<0.05）,and the lowest malondialdehyde（MDA）concentrationwas found in 97.70 mg/kg Fe group（P<0.05）.Dietary Fe levels did significantly influence the relative expression levels of cytoplasmic manganese superoxide dismutase（c Mn-sod）,catalase（cat）and glutathione peroxidase（gpx）in hepatopancreas,and the highest expression levels of c Mn-sod,cat and gpx were found in 218.9 mg/kg Fe group（P<0.05）.Crabs fed the diet containing 132.1 mg/kg Fe had the higher acid phosphatase（ACP）and alkaline phosphatase（AKP）activities in hepatopancreas and serum mg/kg than those fed the other diets（P<0.05）.The lowest activity of nitric oxide synthase（NOS）in serum was observed in crabs fed diet containing 132.1 mg/kg iron group was the（P<0.05）.The expression levels ofα₂-macroglobulin（α₂-M）,crustin and akp in hepatopancreas were significantly affected by different Fe levels（P<0.05）.Based on broken-line and quadratic regression analysis of PWG against dietary Fe levels,the optimum Fe requirement were estimated to be 227.98 and 210.20 mg/kg for juvenile swimming crab.When dietary Fe levels ranged from 97.7 mg/kg to 218.9 mg/kg,the antioxidant and non-specific immune capacities were significantly improved.2.An 8-week feeding trial was conducted to evaluate effects of dietary Mn levels on growth performance,mineral bioaccumulation in tissue,innate immune response and antioxidant capacity of juvenile swimming crab.Six experimental diets were formulated to contain graded levels of Mn（manganese sulfate monohydrate as Mn source）,the analyzed Mn levels were 9.8,20.2,29.7,38.2,65.6 and 123.6 mg/kg,respectively.There were three replicates in each diet and 10swimming crabs（initial body weight was 9.00±0.14g）in each replicate.The results of present study showed that PWG and SGR were significantly influenced by dietary Mn levels,the highest PWG and survival rate were observed in crabs fed the diet containing 38.2 mg/kg Mn,mg/kgand significantly higher survival than those fed the diet containing 123.6 mg/kg Mn（P<0.05）.Crabs fed the diet containing 123.6 mg/kg Mn had higher Mn concentration in muscle and carapace than those fed the other diets（P<0.05）.However,the highest Mn concentration in hepatopancreas was observed in crab fed the diet with 65.6 mg/kg Mn.Moreover,the lowest activities of anti-oxidation enzymes including Mn-SOD,CAT,and T-AOC were occurred at crabs fed the dietary 9.8 mg/kg Mn.Crabs fed the 9.8 mg/kg Mn diet exhibited lower relative expression levels in hepatopancreas of genes related to antioxidant ability such as c Mnsod,gpx,prx,and cat mg/kgwhen compared to the other diets,and the highest expression levels were recorded in crabs fed the diet contenting 38.2 mg/kg Mn.Crabs fed the diet contenting 38.2mg/kg Mn had the highest the AKP activity in serum among all treatments（P<0.05）.,The relative expression levels of crustin,acp and akp in hepatopancreas were significantly up-regulated and then down-regulated with the increase of dietary Mn levels,and crabs fed the 65.6mg/kg Mn diet exhibited the highest expression level of crustin（P<0.05）.However,the highest expression levels of acp and akp were observed in crabs fed the 38.2 mg/kg diet（P<0.05）.In conclusion,based on linear broken-line and quadratic broken-line regression analysis of PWG against dietary Mn levels,the optimum Mn requirement were 48.02 and 53.30 mg/kg for juvenile swimming crab,respectively.Dietary appropriate Mn levels could improve the antioxidant and non-specific immunity capacity.