| Free radicals are produced by animals in the process of growth and metabolism. Normally, the produce and removal of free radicals achieve a balance. In the case of intensive aquaculture, aquatic animals are susceptible to stress such as temperature, density, ammonia nitrogen, the balance is skewed to the produce of free radicals. If the free radicals can’t be mopped up timely and effectively, the cell membranes will be damaged by peroxidation. Therefor, it is necessary that antioxidant enzymes retain high activity. The proper addition of cofactor can maintain there activity.Glutathione is a kind of small sulfhydryl antioxidants which widely exists in eukaryotic cells. Glutathione can be used as the substrate of glutathione peroxidase to prevent lipid peroxidative. It is mark of oxidation resistance to maintain the level of glutathione and perform efficiently. To maintain the activity of glutathione synthase and glutathione peroxidase can ensure the level and effect of glutathione. Magnesium and selenium are coenzymes of the two enzymes respectively, therefore, proper addition of the two minerals.The Chinese mitten crab (Eriocheir sinensis) is an important economic aquatic animal farmed in China. The juvenile Chinese mitten crab was selected as the objectin these experiments. Experiments were been conducted to investigate the effects of dietary selenium and magnesium supplementation on the growth performance, body composition and antioxidant status of juvenile Chinese mitten crab. In order to know the joint supplemental effects of selenium and magnesium, an8-week feeding experiment was followed to study the effect of organic magnesium and organic selenium on the growth performance and antioxidation system of Eriocheir sinensis. The effect of magnesium sources on the Chinese mitten crab was also conducted. Four main conclusions can be summarized as follows:1. Growth, body composition and anti-oxidative status of juvenile Chinese mitten crab, Eriocheir sinensis, fed different selenium levels of dietsChinese mitten crab is an importantly economic aquatic animal farmed in China and is becoming a worldwide food due to its increasing export. In the present study, a6-weeks feeding trial has been conducted to investigate the effects of dietary Se supplementation on the growth performance, body composition and antioxidant status of juvenile Chinese mitten crab. Six diets containing0,0.2,0.4,0.6,0.8and1.0mg/kg selenium were fed to quadruplicate juvenile Chinese mitten crab Eriocheir sinensis (0.27±0.01g), respectively,30in every aquarium. Crab fed0.4mg/kg diet obtained the highest weight gain, survival rate, and whole body crude protein content among the various groups (P＜0.05). Hepatopancreas and muscle selenium contents were positively related to the dietary Se supplementation. Both serum and hepatopancreas glutathione peroxidase activities increased with dietary Se level increase, and peaked at0.4mg/kg. But with dietary Se increased to0.8mg/kg, serum glutathione peroxidase activity decreased significantly (P<0.05). The contents of malonaldehyde first decreased and then increased with the increase of dietary Se supplementation. Crab fed0.4mg/kg diet had the lowest malonaldehyde activity value, and differed from that of the control and1.Omg/kg groups (P<0.05). Crabs fed diet containing or less than0.6mg/kg selenium had lower glutathione contents than crabs fed0.8mg/kg and1.0mg/kg groups (P<0.05). The results indicated that dietary selenium supplementation of0.4-0.6mg/kg (total selenium is0.43-0.66mg/kg) can promote the growth, the utilization of dietary protein and anti-oxidative ability of juvenile Chinese mitten crab. Quadrate broken line analysis with weight gain shows that a level of0.51mg/kg selenium supplementation (total selenium is0.59mg/kg) can meet the optimal growth of juvenile Chinese mitten crab.2. Growth, body composition and anti-oxidative status in juvenile Chinese mitten crab, Eriocheir sinensis fed diets with different magnesium levelsTo determine dietary magnesium (Mg) requirements of juvenile Chinese mitten crab L-aspartic acid magnesium at0,1.5,3.0,4.5,6.0,7.5g/kg diet. Each diet was fed to five replicate groups of juvenile Chinese mitten crab[initial body weight:(2.97±0.01) g] in a closed, recirculating rearing for ten weeks. Growth performance, contents of crude protein and reduced glutathione in hepatopancreas and serum were highest in crabs fed the diet supplemented with3.0g/kg. The malonaldehyde in hepatopancreas and serum were also the lowest in this group (P<0.05). The content of GSH of hepatopancreas and serum increased and then decreased with the increase of magnesium supplementation (.P＜0.05). Ca concentrations and Ca/Mg in whole body was higher in basal feed group than any other groups. Comprehensive analysis of various indicators,3.0g/kg Mg should be supplied in the diet.3. Effect of organic Mg and organic Se on the antioxidation capability of juvenile Chinese mitten crab, Eriocheir sinensis An8-week feeding experiment was conducted to study the effect of organic magnesium and organic selenium on the growth performance and antioxidation system of Chinese mitten crab. The four treatments were control, organic Se, organic Mg and combination of organic Se and Mg. The supplementation level of organic Se was0.4mg/kg, and that of organic Mg was0.3%. The initial body weight of crab was (0.05±0.01) g. The results showed that with the supplement of organic Se, feed coefficient and reactive oxygen species (ROS) in the serum were significantly decreased, meanwhile, the total antioxidant capability (T-AOC) and the content of glutathione (GSH) in the serum were improved significantly (P<0.05). The content of GSH and T-AOC in the serum and hepatopancreas for the crabs fed organic Mg increased significantly, which might be the cause of significant decrease of the ROS and MDA(P<0.05). The joint supplementation of selenium and magnesiumcan significantly increase weight gain rate, anti-oxidation ability and decrease the feed coefficient of juveniles.4. Effect of magnesium sources on the growth performance, body composition and antioxidation capability of Chinese mitten crab (Eriocheir sinensis)The experiment was conducted to study the effect of magnesium sources on the growth performance, body composition and antioxidation system of Chinese mitten crab. Crabs were fed diets supplemented with magnesium sulfate (MgSO4), magnesium acetate (MgAC) or magnesium L-aspartate (MgAsp) at level of3.0g/kg diet. The initial body weight of crab was (0.05±0.01)g, respectively,30in every aquarium. The results showed that the weight gain rate of crabs were lowest with the supplement of MgSO4, meanwhile, feed coefficient in this group was higher significantly than the other two groups (P＜0.05). Moisture content of the crabs fed MgSO4was higher than the other two groups, but the contents of crude protein and lipid (P<0.05). The total antioxidant capacity and content of reduced glutathione were highest in crabs fed MgAsp, meanwhile, the content of reactive oxygen and malondialdehyde was significantly lower than the other two groups (P<0.05). In conclusion, organic magnesium such as MgAC and MgAsp were more effective to increase growth, improve body composition and increase anti-oxidation ability, and MgAsp was better than MgAC. |
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