A 12-week growth trial was conducted in a flow-through system to determine dietary selenium (Se) requirement for on-growing gibel carp (initial body weight: 76.2 +/- 0.05 g, mean +/- SEM). Selenomethionine was supplemented to the basal diet to formulate seven semi-purified diets containing 0.26, 0.58, 0.72, 1.14, 1.34, 1.73 and 2.09 mg Se kg(-1) diet. The results showed that plasma superoxide dismutase (SOD) activity significantly increased when fish were fed with 0.58 mg Se kg(-1) diet (P < 0.05) and then decreased at 2.09 mg Se kg(-1) diet (P < 0.05). Plasma T-AOC activity was higher in fish fed with 0.72 mg Se kg(-1) diet (P < 0.05) and plasma malondialdehyde (MDA) was higher in fish fed with 0.26 mg Se kg(-1) diet (P < 0.05). When fish were fed 1.14 mg Se kg(-1) diet, hepatic GSHPx, T-AOC, GSH and CAT activities were significantly higher than those fed with 0.26 mg Se kg(-1) diet (P < 0.05). Hepatic superoxide dismutase (SOD) activity was higher at 1.34 mg Se kg(-1) diet (P < 0.05). Fish liver Se concentrations were significantly higher when fed with 0.72 mg Se kg(-1) diet (P < 0.05) and then kept constant when Se >= 0.72 mg kg(-1) (P > 0.05). Whole-body and muscle Se concentrations were higher when fed with 1.34 mg Se kg(-1) diet (P < 0.05) and kept a plateau when Se >= 1.34 mg kg(-1) (P > 0.05). In conclusion, based on broken-line regression of hepatic Se concentrations, hepatic SOD activity and hepatic T-AOC activity, dietary Se requirements for on-growing gibel carp was 0.73 mg kg(-1), 1.12 mg kg(-1) and 1.19 mg kg(-1) diet respectively.