| Feeding experiments were conducted to determine the effects of dietaryα-lipoic acid, glutathione and selenium on growth and antioxidative responses of abalone, Haliotis discus hannai Ino. Results of the studies are presented as follows:1. A feeding experiment was conducted to determine the effects ofα-lipoic acid (LA) on growth and antioxidative responses of juvenile abalone Haliotis discus hannai Ino. Six purified diets supplemented with 0,200,400,800,1600 and 3200 mg/kg of LA, respectively, were fed to abalone for 16 weeks in a flow-through water system. The results showed that the weight gain ratio (WGR) increased with increasing dietary LA levels, and reached the highest value in the group with 800 mg/kg dietary LA supplementation. Glutathione peroxidase (GPX) activity in 800 mg/kg dietary LA group was significantly higher than that in 0 mg/kg group. Supplements of 200,400,800 mg/kg dietary LA significantly elevated the total antioxidative capacity (T-AOC) and superoxide dismutase (SOD) activities compared with the 0 mg/kg group. Glutathione (GSH) level in hepatopancreas significantly increased with dietary LA supplements in a dose-dependent manner (except for the 200 mg/kg group). Catalase (CAT) and malondiadehyde (MDA) in hepatopancreas were not significantly affected by dietary LA. In conclusion, dietary LA promoted the growth and stimulated the antioxidative defense capacity of abalone. Based on data of WGR, the optimal dietary LA supplement for juvenile abalone was found to be 709 mg/kg using broken-line analysis.2. A feeding experiment was conducted to determine effects of glutathione on growth and antioxidative responses of abalone. Six semi-purified diets containing different concentrations of glutathione 0,83.7,165.0,332.4,578.5,884.9 mg/kg) were fed to abalone (initial weight:0.43±0.00 g) for 16 weeks in a flow-through water system. Each diet was fed to one triplicate group of abalone randomly. The results showed that there were no significant differences in weight gain rate (WGR) of abalone among different treatments. Glutathione peroxidase (GPX), catalase (CAT), superoxide dismutase (SOD), total antioxidative competence (T-AOC), glutathione (GSH) and malondiadehyde (MDA) levels in hepatopancreas were detected in this experiment. Dietary glutathione (165.0,332.4 mg/kg) significantly increased GPX activity in hepatopancreas compared with 0 mg/kg supplemental group. SOD activity reached the highest value in 332.4 mg/kg glutathione group, and followed by 83.7,165.0 and 578.5 mg/kg groups, each of which was higher than that in 0 mg/kg group. T-AOC firstly increased with increasing level of dietary glutathione, and then decreased, the highest value was found in abalone fed diet with 165.0 mg/kg glutathione group and the lowest in 884.9 mg/kg group. On the contrary, CAT firstly decreased when dietary glutathione was less than 884.9 mg/kg and then increased with increasing dietary glutathione up to 884.9 mg/kg. Glutathione in hepatopancreas increased with the increasing level of dietary glutathione. No significant differences were found in MDA level. For abalone, the optimum level of dietary glutathione was 350～400 mg/kg based on all the biochemical parameters.3. A 2×3 two-factorial experiment was designed to investigate effects of dietary selenium and a-lipoic acid on antioxidative responses of abalone Haliotis discus hannai (initial weight:0.43±0.00 g). Six semi-purified diets were formulated to provide graded levels of selenium (0 and 1 mg/kg) and a-lipoic acid (0,800 and 3200 mg/kg). Each diet was fed to a triplicate group of abalone for 16 weeks in a flow-through water system. The results showed that when diet contained noα-lipoic acid, dietary selenium significantly improved glutathione peroxidase (GPX) and total antioxidative capacity (T-AOC) in hepatopancreas compared with selenium deficient groups. At each selenium level, diet containing 800 mg/kgα-lipoic acid significantly improved superoxide dismutase (SOD), GPX and T-AOC value in hepatopancreas, respectively, and glutathione in hepatopancreas were also increased although no significant differences were found among treatments. But diet with 3200 mg/kg a-lipoic acid significantly decreased GPX and T-AOC in hepatopancreas. Although no statistically significant interaction was found, dietary selenium and a-lipoic acid showed potential interaction on antioxidative responses of abalone. Based on these results, abalone fed diet supplemented with 1 mg/kg Selenium and 800 mg/kgα-lipoic acid showed better antioxidative responses.
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