| Eriocheir sinensis, also known as Chinese mitten crab, belongs to Grapsidae family of Decapoda crustaceans, is considered to be one of the most important aquatic species for aquaculture due to its desirable taste and high economic value. According to the data by FAO in 2014, the capture production of E. sinensis is just only 61.3 thousand tons in 2012 and is not satisfy the demand of people. Therefore, large scale farming is becoming more and more important in E. sinensis. In recent years, the aquaculture production of E. sinensis increased dramatically, and in 2013, the production of E. sinensis is over 720,000 tons and the economic value is over 5.0 billion dollars. However, with the development of intensive aquaculture, the artificial feed is still a problem need to be solved. Up to now, the scholars have made a lot of research on the requirements and nutrition physiology of protein, lipid and carbohydrate in E. sinensis, but data on dietary trace element requirement is limited. In this paper, the aim is to determine dietary folic acid requirement, and its effects on non-specific immunity and disease resistance, the interactive effects of folic acid and vitamin B12 and the effects of dietary folic acid on the ability of anti-nitrite stress in juvenile E. sinensis. These results enrich the nutritional physiology data on trace element of crab and shrimp, and provide a theoretical basis for the development of artificial feed of E. sinensis.1. Dietary folic acid requirement of juvenile Chinese mitten crab, Eriocheir sinensis, and its effects on non-specific immunity and disease resistance1.1 Effects of dietary folic acid levels on growth performance, body composition and antioxidant capacity of juvenile Chinese mitten crab, Eriocheir sinensisThis study was to determine the dietary folic acid requirement of juvenile Chinese mitten crab, Eriocheir sinensis, and its effects on growth performance, body composition and antioxidant status. Folic acid was added to a semi-purified basal diet with seven levels (0,0.5,1.0,2.0,4.0,8.0,16.0 mg folic acid/kg diet) and a diet free of folic acid and vitamin B12 was also included as a control. Each diet was fed to E. sinensis (initial weight,0.051±0.001 g) in four replicates for 8 weeks. Results showed that weight gain rate, special growth rate and feed efficiency were significantly greater in crabs fed the diets containing≥2.0 mg folic acid/kg than the other groups, but there was no significant difference between crabs fed≥2.0 mg folic acid/kg. The whole body crude protein and crude lipid were significantly higher in the crabs fed the diets containing≥2.0 mg folic acid/kg diet than the other groups. Moisture and ash were not affected by dietary folic acid levels. The superoxide dismutase activity and glutathione S-transferase activity were highest in crabs fed the diets with≥2.0 mg folic acid/kg diet, followed those fed 0.5 and 1.0 mg folic acid/kg, and the lowest occurred in the control group. The malondialdehyde content was highest in crabs fed the control diet, followed by those fed 0 mg folic acid/kg, and the lowest occurred in ≥0.5 mg folic acid/kg groups. The optimum dietary folic acid requirement by E. sinensis was estimated at 2.29-2.52 mg/kg diet.1.2 Effects of dietary folic acid levels on non-specific immunity and disease resistance of juvenile Chinese mitten crab, Eriocheir sinensisIn this study, a diet free of folic acid and vitamin B12 was used as a control to determine the effects of dietary folic acid on non-specific immune and disease resistance of E. sinensis. Results showed that the malondialdehyde content was highest in crabs fed the control diet, followed by those fed 0 mg folic acid/kg, and the lowest occurred in ≥0.5 mg folic acid/kg groups. Phenoloxidase activity and total hemocyte count were significantly higher in crabs fed diets with ≥2.0 mg folic acid/kg than those in other groups. Crabs fed 2.0 mg folic acid/kg had the highest lysozyme, acid phosphatase and alkaline phosphatase activities but the lowest cumulative mortality.2. The interactive effects of dietary folic acid and vitamin B12 on growth performance and immune responses of juvenile Chinese mitten crab, Eriocheir sinensis2.1 Dietary vitamin B12 requirement of juvenile Chinese mitten crab, Eriocheir sinensisAn 8-week feeding trial was conducted to investigate the optimum dietary vitamin B12 requirement of juvenile Chinese mitten crab, Eriocheir sinensis, and its effect on non-specific immunity responses and resistance against Aeromonas hydrophila. Vitamin B12 was added to the basal diet at the supplementation of 0,0.05, 0.1,0.2,0.4,0.8 and 1.6 mg/kg to formulate seven semi-purified diets, and a folic acid and vitamin B12 free diet was also included in this study as a control. Each diet was fed to 4 replicates of E. sinensis (initial weight,0.051±0.001 g), and challenge study for 2 weeks. Results showed that weight gain rate and special growth rate were best in crabs fed 0.2 and 0.4 mg vitamin B12/kg diets, followed by 0,0.5,0.8 and 1.6 mg/kg groups and lowest in the control group. The feed efficiency and survival rate peaked at the supplementation of 0.2 mg/kg diet. The whole body crude protein and crude lipid of juvenile crabs were significantly higher when crabs fed 0.2-0.8 mg vitamin B12/kg than those fed the diets without vitamin B12 supplement. Total hemocyte count was significantly higher in crabs fed 0.2 and 0.4 mg vitamin B12/kg diets than those fed other group diets, and crabs fed the 0.2 mg/kg diet had the highest phenoloxidase, lysozyme, acid phosphatase and alkaline phosphatase activities but the lowest cumulative mortality. The optimum dietary folic acid requirement by E. sinensis was about 0.20-0.22 mg/kg.2.2 The interactive effects of dietary folic acid and vitamin B12 on growth performance, non-specific immunity and disease resistance of juvenile Chinese mitten crab, Eriocheir sinensisThe present study was aimed to determine the interactive effects of dietary folic acid and vitamin B12 on growth performance, non-specific immunity and disease resistance of juvenile Chinese mitten crab Ericheir sinensis. The crabs (initial weight, 2.57±0.02 g) were fed 4 experimental diets containing 2 levels of folic acid (0 and 2.3 mg folic acid/kg diet) and vitamin B12 (0 and 0.2 mg vitamin B12/kg diet) in 5 replicates for 8 weeks, and followed by an Aeromonas hydrophila challenge study for 2 weeks. Results showed that weight gain, specific growth rate, feed efficiency and survival were significantly higher in E. sinensis fed diet with 2.3 mg folic acid/kg and 0.2 mg vitamin B12/kg than those fed the diet without folic acid and vitamin B12 supplementation. The phenoloxidase activity was peaked in juveniles fed diet with 2.3 mg folic acid/kg and 0.2 mg vitamin B12/kg, and total hemocyte count, lysozyme, acid phosphatase and alkaline phosphatase activities were highest in crabs fed diet with both folic acid and vitamin B12 supplementation, followed by crabs fed diet with only folic acid or vitamin B12supplementation, and lowest occurred in the group without folic acid and vitamin B12 supplementation. Crabs fed diet with 2.3 mg folic acid/kg and 0.2 mg vitamin B12/kg had the highest superoxide dismutase activity but the lowest malondialdehyde content and the cumulative mortality. These results indicated that folic acid and vitamin B12 have an interaction effect on growth performance, non-specific immunity and disease resistance of juvenile E. sinensis and the optimum dietary folic acid and vitamin B12 concentrations of juveniles were recommended at 2.3 mg/kg diet and 0.2 mg/kg diet, respectively.3. Effects of dietary folic acid on growth, antioxidant capacity and non-specific immune response of juvenile Chinese mitten crab Eriocheir sinensis exposed to nitriteAn 8-week study was conducted to determine the effects of dietary folic acid on growth, antioxidant capacity and non-specific immune response of juvenile Chinese mitten crab Eriocheir sinensis exposed to nitrite. Juvenile E. sinensis (initial weight 0.14±0.02 g) were fed a basal diet supplemented with three folic acid levels (0,2.5 and 8.0 mg/kg diet) and exposed to three concentrations of nitrite (0,0.2 and 2.0 mg/L). Results indicated that weight gain was significantly higher in juveniles exposed to 0 and 0.2 mg/L nitrite than those exposed to 2.0 mg/L nitrite. Feed efficiency and survival were significantly higher in juveniles fed the diets with 2.5 and 8.0 mg folic acid/kg diet than those fed the diet with 0 mg folic acid/kg diet, and significantly higher in crabs exposed to 0 mg/L nitrite than those exposed to 2.0 mg/L nitrite. The superoxide dismutase and catalase activities were significantly higher in E. sinensis fed the diets with 2.5 and 8.0 mg folic acid/kg diet than crabs fed the diet with 0 mg folic acid/kg diet, and highest in crabs exposed to 0 mg/L nitrite, followed by 0.2 mg/L groups, and lowest in 2.0 mg/L groups. While the malondialdehyde content was significantly higher in juveniles fed the diet with 0 mg folic acid/kg diet than the other groups, and highest in crabs exposed to 2.0 mg/L nitrite, followed by 0.2 mg/L groups, and lowest in 0 mg/L groups. Phenoloxidase and alkaline phosphatase activities were significantly higher in E. sinensis fed the diets with 2.5 and 8.0 mg folic acid/kg diet than that fed the diet with 0 mg folic acid/kg diet, while total hemocyte count, lysozyme and acid phosphatase activities were highest in crabs fed the diet with 8.0folic acid/kg diet, followed by 2.5 mg/kg groups, and lowest in 0 mg/kg groups. Moreover, total hemocyte count, phenoloxidase, lysozyme, acid and alkaline phosphatase activities were significantly higher in juveniles exposed to 0 mg/L nitrite than the other groups. All the results demonstrated that dietary folic acid could improve the non-specific immune responses in E. sinensis under nitrite stress. |
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