The effects of dietary cadmium (Cd) supplementation on growth, antioxidant capacity and accumulation of Cd in tissues (body wall, digestive tracts, and respiratory tree) of sea cucumber, Apostichopus japonicus, exposed to sub-chronic concentrations (0, 10, 50, 100, and 500 mg Cd/kg dry weight) of Cd were investigated. In addition, the potential protective effects of vitamin C (L-ascorbic acid, AsA) against the effects of Cd on sea cucumbers were investigated. Sea cucumbers were exposed to dietary Cd for 30 days, after which another group of healthy sea cucumbers was supplied diet supplemented with mixed Cd and AsA for another 30 days. Cd exposure for 30 days resulted in increased Cd accumulation in tissues of sea cucumbers with exposure time and concentration. The order of Cd accumulation in organs was digestive tracts > respiratory tree > body wall. On day 30, the body weight gain (BWG) and specific growth rate (SGR) decreased significantly (P < 0.05) in the 500 mg Cd/kg treatment. Superoxide dismutase (SOD) activity, glutathione peroxidase (GSH-Px) activity and catalase (CAT) activity in the coelomic fluid of sea cucumbers decreased with increasing dietary Cd concentration, but malondialdehyde (MDA) content in the coelomic fluid increased. Providing diet supplemented with Cd and AsA indicated that although sea cucumbers exhibited signs of Cd toxicity, no death occurred in response to 50 mg Cd/kg for 30 days. Based on these findings, five treatments were provided: 50 mg Cd/kg+0 mg AsA/kg, 50 mg Cd/kg+3000 mg AsA/kg, 50 mg Cd/kg+ 5000 mg AsA/kg, 50 mg Cd/kg+10,000 mg AsA/kg, and 50 mg Cd/kg+15,000 mg AsA/kg. The BWG and SGR of sea cucumbers fed the MA supplemented diet mixed with Cd increased. Additionally, MDA levels in coelomic fluid were negatively correlated with dietary AsA levels, while antioxidant capacities (SOD, GSH-Px and CAT) were positively correlated with dietary AsA levels. Moreover, Cd accumulation in tissues decreased in response to dietary AsA supplementation of treatments. Overall, antioxidant capacity and bioaccumulation in sea cucumber was found to decrease and be induced in response to Cd, but vitamin C mitigated these effects, with 5000 mg AsA/kg providing the optimum protection against 50 mg/kg Cd. (C) 2016 Elsevier Inc. All rights reserved.