| Iron is an indispensable trace element for animals to maintain basic life activities,which plays an essential role in bio-oxidation,DNA synthesis and repair.Meanwhile,iron is also closely related to anti-infection ability and immunity of animals.Dietary iron deficiency affects numerous physiological metabolic processes,leading to the decreased growth performance,lower resistance to pathogen and other negative effects,whereas iron excessive is closely related to many diseases.In aquatic animals,many studies have shown that dietary iron could affect the growth performance,immunity,haematological parameters and antioxidant capacity of fish.However,the physiological function of dietary iron has not been explored in Chinese mitten crab（Eriocheir sinensis）,an important freshwater economic crustacean species in China.Therefore,this study determined the optimal dietary iron level for juvenile E.sinensis for the first time,and investigated the effects of iron deficiency and excess on juvenile E.sinensis.Based on the adverse effects of iron deficiency and iron excess,the strategies to improve iron absorption and utilization under appropriate iron levels were explored.By comparing the effects of different iron sources on growth performance,iron absorption and utilization,antioxidant capacity and immunity of juvenile E.sinensis,we evaluated and obtained the optimal iron source.In addition,the effects of vitamin C on iron metabolism of juvenile E.sinensis fed with different iron levels were studied in order to improve iron absorption and utilization,thereby promoting growth performance and immunity.The results supplemented the theoretical research of dietary iron in E.sinensis,and provided a reference for promoting dietary iron absorption and utilization reasonably and efficiently.1.Evaluation of the optimum dietary iron level and its immunomodulatory effects on juvenile Chinese mitten crab,Eriocheir sinensisThis study evaluated the effects of dietary iron levels on growth,antioxidant status and non-specific immunity in juvenile E.sinensis.A 56-day feeding trial containing six experimental diets containing different iron levels（64,89,130,177,271 and 508 mg/kg）was conducted.Juvenile crabs fed the 177 mg/kg iron diet had the highest weight gain,specific growth rate and the lowest feed conversion ratio.A positive correlation was observed between the iron content in the whole body and hepatopancreas with dietary iron supplementation.The catalase activities,total antioxidant capacity,superoxide dismutase and glutathione peroxidase in the hepatopancreas were significantly increased in 89-177 mg/kg iron diets.In addition,the non-specific immunity of the crabs was also improved with the increasing level of dietary iron supplementation.Broken-line analysis on weight gain,specific growth rate and iron level in the hemolymph against dietary iron levels indicates that the optimal iron requirement for juvenile crabs ranged from 133 to 141 mg/kg when using ferrous sulfate as iron source.According to intestinal microflora analysis,dietary iron deficiency and excess would change the intestinal microflora structure,leading to the decreased beneficial bacteria,and the increased pathogenic bacteria.The highest transcription of inflammationrelated genes in the hepatopancreas was found in the crabs fed 64 mg/kg iron diet under the lipopolysaccharide（LPS）stimulation.Meanwhile,the transcription of iron regulatory protein had a decreasing trend while that of Ferritin-1 and Ferritin-2 had an increasing trend regardless of the lipopolysaccharide and phosphate buffer saline treatment,it suggested that proper dietary iron could enhance the resistance of crabs to LPS.This study provided a basic reference for the precise nutrition requirements of dietary iron and the formulation of feed in E.sinensis.2.Effects of different iron sources on growth performance,iron absorption and utilization,antioxidant capacity and non-specific immunity in Eriocheir sinensisThis study was conducted to determine the effects of different iron sources on the growth performance,iron absorption and utilization,antioxidant capacity and nonspecific immunity in E.sinensis.Juvenile crabs（3.29±0.06 g）were fed with three basic diets supplemented with 100 mg/kg iron in the form of ferrous sulfate（S-100）,ferrous fumarate（F-100）and ferrous glycine（G-100）for 70 days.The crabs in the G100 group had higher weight gain,specific growth rate and lower whole-body total lipid than those in the S-100 group.The expression levels of divalent metal ion transporter 1 and ferroportin in the intestine and hepatopancreas,and iron content in tissues were significantly enhanced in the G-100 group compared with the S-100 group.Besides,the total antioxidant capacity,the activities of acid phosphatase and phenoloxidase in the G-100 group were significantly improved compared with the S-100 group.The mRNA levels of Toll,Myd88,Imd,Relish and Jnk in the hepatopancreas of crabs fed G-100 diet significantly decreased to resist the LPS challenge.In a word,this study demonstrated that ferrous glycine might be the proper iron source for improving growth performance,iron utilization,antioxidant capacity and non-specific immunity of E.sinensis,and can be a source of effective iron supplementation in aquafeed.3.Effects of dietary supplementation with iron and vitamin C on growth performance,iron absorption and utilization,antioxidant capacity and nonspecific immunity in Eriocheir sinensisThis study was conducted to evaluate the effects of dietary supplementation with iron and vitamin C on the growth performance,iron absorption and utilization,antioxidant capacity and non-specific immunity of E.sinensis.Six diets supplemented with two vitamin C（0 and 700 mg/kg）levels and three iron（0,50 and 100 mg/kg）levels were fed to juvenile（1.14±0.01g）for 56 days.Crabs fed 0 mg/kg iron diet had the lowest weight gain,specific growth rate and had the highest feed conversion rate regardless of dietary vitamin C levels.Dietary vitamin C significantly improved the weight gain,specific growth rate and decreased feed conversion rate when supplemented with 0 and 100 mg/kg iron.At 50 and 100 mg/kg iron diets,the mRNA levels of divalent metal ion transporter 1 and Ferroportin in the intestine and hepatopancreas,hemolymph iron content and transferrin content were significantly enhanced when supplemented with vitamin C.Moreover,iron deficiency decreased the superoxide dismutase activity and increased the malondialdehyde content in the hepatopancreas of crabs fed 0 mg/kg iron diet.Dietary vitamin C also increased the acid phosphatase and bacteriolytic activities when supplemented with 0 and 100 mg/kg iron.In addition,crabs fed 100 mg/kg iron and 700 mg/kg vitamin C diet had the highest survival rate after Aeromonas hydrophila challenge.This study demonstrated that 700 mg/kg vitamin C could promote the iron absorption and utilization,thereby increase the growth performance,immunity and resistance to Aeromonas hydrophila challenge of E.sinensis. |
PDF Full Text Request