Evaluation of the optimum dietary iron level and its immunomodulatory effects on juvenile Chinese mitten crab, Eriocheir sinensis

This study evaluated the effects of dietary iron levels on growth, antioxidant status and non-specific immunity in juvenile Chinese mitten crab (Eriocheir sinensis). A 56-day feeding trial containing six experimental diets supplemented with six iron levels (0, 30, 60, 120, 240, 480 mg/kg) was conducted. The crabs fed the 177 mg/kg iron diet had significantly higher weight gain and specific growth rate and lower feed conversion ratio compared with those fed the 64 and 508 mg/kg iron diets. 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 (P < 0.05). 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 130 to 141 mg/kg. The transcription of iron regulatory protein had a decreasing trend while that of ferritin-land ferritin-2 had an increasing trend regardless of the lipopolysaccharide and phosphate buffer saline treatment. The highest transcription of inflammation-related genes in the hepatopancreas was found in the crabs fed diets without iron supplementation under the lipopolysaccharide stimulation. Our results indicate that the optimal iron requirement for juvenile crabs was in the range of 130-141 mg/kg and dietary iron plays an indispensable role in the innate immune system in E. sinensis.