Studies On Nutritional Physiology Of Selenium And Manganese For Cobia (rachycentron Canadum)

10-week feeding trials were conducted to investigate the nutritional physiology of selenium and manganese for cobia (Rachycentron canadum). The dietary requirements of selenium and manganese for cobia (average initial weight:about 6 g) were estimated with different indicators. The experiments were conducted in indoor culture system (500 L/tank). Results of these studies are presented as follows:1. A 10-wk feeding trial was conducted to estimate the optimum dietary selenium requirement for juvenile cobia, Rachycentron canadum L. The basal diet was formulated to contain 50.6% crude protein from vitamin-free casein, gelatin. Seleno-DL-methionine was added to the basal diet at 0.00 (control group),0.20, 0.40,0.60,0.80 and 1.00 mg Se kg-1 diet providing 0.21,0.35,0.62,0.85,1.07 and 1.36 mg Se kg-1 diet, respectively. Each diet was randomly fed to triplicate groups of juvenile cobia with initial weight 6.27±0.03 g in a flow-through system. The Selenium concentration in rearing water was monitored during the feeding period, and was not detectable. Dietary selenium level significantly influenced survival, specific growth rate (SGR), feed efficiency ratio (FER) and the selenium concentrations in the whole body and vertebra of cobia. The selenium-dependent glutathione peroxidase (Se-GPx, EC 1.11.119) activity increased with the increase of dietary selenium levels (P<0.05). Hepatic glutathione reductase (GR, EC 1.6.4.2) activity was highest in fish fed diet with 0.21 mg Se kg-1, and declined with the increase of dietary Se levels(P<0.05). Base on broke-line regression of SGR, selenium concentration in whole body and vertebra, the selenium requirements of juvenile cobia were 0.788,0.793 and 0.811 mg Se kg-1 diet in the form of Seleno-DL-methionine, respectively.2. A 10-wk feeding trial was conducted to estimate the optimum dietary manganese requirement for juvenile cobia, Rachycentron canadum L. The basal diet was formulated to contain 50.1% from vitamin-free casein, gelatin, fish protein concentrate. Manganese sulfate was added to the basal diet at 0.00 (control group),6,12,18,24 and 36 mg Mn kg-1 diet providing 5.98,7.23,16.05,23.87, 28.87 and 41.29 mg Mn kg-1 diet, respectively. Each diet was fed to three replicate groups of cobia for 9 weeks, and each tank was stocked with 30 fish (initial weight:6.27±0.01g). The Manganese concentration in rearing water was monitored during the feeding period, and was<0.01 mg/L). Dietary manganese level significantly influenced survival (SR), specific growth rate (SGR), feed efficiency ratio (FER) and the manganese concentrations in the whole body and vertebra of cobia. The manganese-Superoxide dismutase (Mn-SOD) activity of liver and serum increased with the increase of dietary manganese level from 5.98mg/kg to 23.87 mg/kg (P<0.05) and then had no significantly difference for the groups fed diets containing higher levels of manganese. Base on broke-line regression of SGR, manganese concentration in whole body and vertebra, the manganese requirements of juvenile cobia were 21.72mg/kg,22.38mg/kg and 24.93mg/kg diet in the form of Manganese sulfate, respectively.