DIETARY SELENIUM REQUIREMENT OF JUVENILE LARGE YELLOW CROAKER LARIMICHTHYS CROCEUS

To study the effects of selenium to the juvenile large yellow croaker Larimichthys croceus, six experimental diets were formulated to contain the following diets with increment levels of selenium 0 (control), 0.05, 0.2, 0.4, 0.6 and 0.9 mg/kg, respectively. The final content of selenium in each diet was 0.08, 0.16, 0.27, 0.44, 0.66, and 0.96 mg/kg, respectively. Each diet was randomly assigned to triplicate groups of 60 large yellow croaker juveniles initial body weight: (9.14 0.09) g. Fish were fed twice daily (5:00 and 17:30) to satiation for 10 weeks. The results showed that the weight gain rate (WG), whole-body, and vertebrae Se concentration significantly increased with the increased dietary selenium levels (P0.05), and no further increases when the dietary Se concentration was 0.27 mg/kg or higher in the diet. No significant differences were found in the survival rate (SR), feed efficiency (FE), body compositions, hepatosomatic index (HSI), viscerosomatic index (VSI), and condition factor (CF) cross the 6 treatment groups (P0.05). The serum glutathione peroxidase (GPX) activity, superoxide dismutase (SOD) activity and total antioxidant capacity (T-AOC) significantly increased with the increasing of dietary selenium levels (P0.05) with the highest activities at 0.44 mg/kg and 0.16 mg/kg of dietary selenium, respectively. The GPX activity, SOD activity, T-AOC, catalase (CAT) activity, and glutathione reductase (GR) activity in liver had a similar trend with serum enzyme activity. The liver glutathione S-transferase (GST) activity significantly decreased with the increasing of dietary selenium levels (P0.05), and then increased (P0.05). The highest activity was found in the highest Se level (0.96 mg/kg). Based on WG, the dietary Se requirement of juvenile large yellow croaker was 0.178 mg/kg. Based on the whole-body and vertebrae Cu concentration, liver GPX activity, the minimum dietary Se requirements were 0.575, 0.387 and 0.440 mg/kg, respectively.