Dietary selenium requirements of juvenile grouper, Epinephelus malabaricus

Two 8-week feeding experiments were conducted to estimate the dietary selenium (Se) requirement of grouper. Selenomethionine was added to the basal diet at 0, 0.5, 1, 2, 3 and 5 mg Se/kg in Exp. 1 and 0, 0.1, 0.2, 0.4, 0.6, 1 and 2 mg Se/kg in Exp. 2 providing 0.21, 0.77, 1.38, 2.02, 2.70 and 4.00 mg Se/kg (Exp. 1) and 0.17, 0.25, 0.39, 0.55, 0.79, 1.23 and 2.10 mg Se/kg (Exp. 2), respectively. Each diet was fed to triplicate groups of fish (mean initial weight: 12.20 ± 0.14 g in Exp. 1 and 11.94 ± 0.15 g in Exp. 2) in a closed, recirculating rearing system. The Se concentration in rearing water was monitored during the feeding period, and was not detectable in both experiments. In Exp. 1, weight gain and feed efficiency (FE) were highest (P < 0.05) in fish fed diet with 0.77 mg Se/kg, followed by fish fed diets with 2.02 and 2.70 mg Se/kg and the unsupplemented basal diet, and lowest in fish fed diet with 4.00 mg Se/kg. Hepatic glutathione peroxidase (GPx) activity was highest in fish fed diets with ≥ 2.02 mg Se/kg, followed by 0.77 and 1.38 mg Se/kg, and lowest in fish fed the basal diet. Fish fed the basal diet had higher hepatic glutathione reductase (GR) activity than fish in all the other dietary groups. In Exp. 2, weight gain and FE were higher in fish fed diets with 0.79 and 1.23 mg Se/kg than fish fed diets with 0.25, 0.55 mg Se/kg and the basal diet. Hepatic GPx activity was highest in fish fed diets with ≥ 1.23 mg Se/kg, followed by 0.79 mg Se/kg, then 0.39 and 0.55 mg Se/kg, and lowest in fish fed the basal diet. Hepatic GR activity was highest in fish fed the basal diet, followed by 0.55 mg Se/kg, and lowest in fish fed diets with ≥ 0.39 mg Se/kg. The adequate dietary Se concentration for growing grouper estimated by weight gain and by linear regression of whole-body Se retention of the fish is about 0.7 mg Se/kg.