Effects of Iron and Vitamin C on Growth Performance, Iron Utilization, Antioxidant Capacity, Nonspecific Immunity, and Disease Resistance to Aeromonas hydrophila in Chinese Mitten Crab (Eriocheir sinensis)

Iron is an essential trace element with an abroad physiological function, and iron deficiency can impair animal health. Vitamin C (VC) has the potential to release iron from diets and increase iron uptake. This study evaluates the effects of dietary iron and vitamin C on the growth performance, iron utilization, antioxidant capacity, and nonspecific immunity of the Chinese mitten crab (Eriocheir sinensis). Juvenile E. sinensis (1.14 +/- 0.01 g) were fed six diets supplemented with three levels of iron (41.40, 92.25, and 143.00 mg/kg), and each iron level supplemented either 4.33 mg/kg or 700.90 mg/kg of vitamin C for 8 weeks. Crabs fed 41.40 mg/kg of iron diet had the lowest weight gain (WG) and specific growth rate (SGR) and had the highest feed conversion rate (FCR) regardless of dietary vitamin C levels. Dietary 700.90 mg/kg of vitamin C improved WG and SGR but decreased FCR when the diets were supplemented with 41.40 and 143.00 mg/kg of iron (P < 0.05). Dietary 700.90 mg/kg of vitamin C significantly improved the expression levels of divalent metal ion transporter 1, ferroportin, and iron regulation protein in the intestine and hepatopancreas when supplemented with 92.25 and 143.00 mg/kg of iron (P < 0.05) and enhanced the transferrin content in hemolymph and iron deposition in the hepatopancreas when supplemented with 92.25 and 143.00 mg/kg of iron (P < 0.05). Crabs fed the diet supplemented with 41.40 mg/kg of iron had the highest malondialdehyde content and the lowest superoxide dismutase activity in the hepatopancreas. Dietary 700.90 mg/kg of vitamin C supplementation also increased the acid phosphatase and bacteriolytic activity when diets were supplemented with 41.40 and 143.00 mg/kg of iron (P < 0.05). In addition, crabs fed 143.00 mg/kg of iron and 700.90 mg/kg of vitamin C diet had the highest survival rate after the Aeromonas hydrophila challenge. This study demonstrates that dietary 700.90 mg/kg of vitamin C could promote iron absorption and utilization, thereby increasing the growth, immunity, and disease resistance of E. sinensis.