The Effects Of Dietary Magnesium,Selenium And Astaxanthin In Juvenile Chinese Mitten Crab Eriocheir Sinensis Exposed To Ambient Stress

The Chinese mitten crab(Eriocheir sinensis)is one of the important economic crustaceans in China.With the extension of intensive and large-scale artificial breeding,the crab breeding industry has been developing rapidly.However,water pollution depressed the growth of crabs,caused the disease frequently,and decreased the breeding efficiency significantly,which seriously hindered the healthy development of the crab breeding industry.To this end,the search for ways to eliminate or mitigate the effects of environmental stress has become an important issue in the sustainable development of current crab industry.In this paper,the effects of dieatary supplementation of inorganic magnesium,selenium and astaxanthin on the growth performance,antioxidant and infective ability of E.sinensis were studied in order to supplement the nutritional and physiological data of E.sinensis under various environmental stress,improve the artificial formula and provide a reference to feed development.The main findings and conclusions are as follows:1.Effects of dietary magnesium on growth and antioxidant activities of E.sinensis under nitrite stressIn this experiment,the three different experimental diets were based on the purified feed,and added different concentrations of magnesium(0,5,10 g/kg respectively in the form of magnesium L-aspartic acid).E.sinensis with the initial weight of(3.15 ± 0.02 g)were cultured under nitric acid salt concentration of 0 and 1.0 mg/L,respectively with the aim to explore whether the feed supplementation of magnesium will relief the disadvantaged effects of nitrite stress.After culturing for 8 weeks,the results showed that;(1)under the nitrite stress,the weight gain rate of the larvae of E.sinensis in the 0 mg/kg of magnesium group was the lowest and it increased with the increasing content of magnesium addition,reached the highest in 10 g/kg group,but there was no significant difference among the other groups(P>0.05).The survival rate of the larvae under nitrite stress without magnesium was lower than that under the normal water(P<0.05).The survival rate increased with the increasing content of magnesium addition.Similarly,the highest feed coefficient also appeared under the nitrite stress without dietary magnesium and the feed coefficient was significantly decreased(P<0.05)in 5 g/kg and 10 g/kg groups respectively.(2)The analysis of crab body composition showed that there was no significant difference in the water content of the crabs between the treatment groups.The crude fat and crude protein were the lowest in the non-added magnesium group(P<0.05),and increased significantly in 5 g/kg and 10 g/kg groups(P<0.05)but shared no difference with the control group(P>0.05).(3)The activity of superoxide dismutase in serum increased under stress,and reached the highest value under the stress in 1.0 mg/kg group,which was significantly higher than that in the untreated group(P<0.05).The content of superoxide dismutase in hepatopancreas showed no difference among groups while the content of MDA increased significantly(P<0.05)and decreased with the increase of magnesium content.The results showed that the growth rate,survival rate,feed utilization and antioxidant properties of the larvae of E.sinensis were significantly inhibited under the nitrite stress,and the addition of magnesium supplemented in diets could alleviate the negative influence of the stress to ensure the healthy growth of young crabs.2.Effects of selenium on the growth,antioxidation and non-specific immunity of E.sinensis crabs under nitrite stressBased on the actual diets,different contents of yeast selenium(0,0.5 and 1.0 mg/kg)were added into the diets and the larvae of E.sinensis with initial weight(2.19± 0.05 g)were fed and cultured under nitrite stress in the concentration of 2.0 mg/L for 8 weeks,taken the freshwater as the control group.The results showed that:(1)there were no significant difference in weight gain rate and survival rate among groups(P>0.05),and the weight gain rate showed an increased trend with the increase of selenium supplementation under stress.Compared with the control group which was fed basal diet under freshwater,the feed coefficient of the stressed group under nitrite stress was significantly increased(P<0.05)at the highest value.The feed coefficient decreased significantly(P<0.05)and showed no difference(P>0.05)with the control group after the content of selenium reached 1.0 mg/kg.(2)Compared with the control group,the activities of SOD in serum and hepatopancreas under stress without selenium treatment were significantly lower(P<0.05),and reached the highest value when the concentration of selenium was 0.5 mg/kg(P<0.05).The content of MDA in serum and hepatopancreas was increased under stress and decreased with the increase of selenium supplementation(P<0.05),and the content of glutathione peroxidase(GPX)in serum was not significantly increased(P>0.05)and in the hepatopancreas showed a significant upward trend(P<0.05).The GPX in serum and hepatopancreas in selenium groups at the content of 0.5 mg/kg and 1.0 mg/kg were also significantly higher than other groups(P<0.05).(3)The total number of blood cells and the oxygen consumption rate of the selenium-supplemented group were decreased,but there was no significant difference.The total number of blood cells in the 0.5 mg/kg group was significantly higher than that in the untreated group(P<0.05).Compared with the control group,serum lysozyme,acid phosphatase and alkaline phosphatase were significantly decreased(P<0.05),and these enzymes except alkaline phosphatase were significantly increased after supplementing with selenium at the content of 0.5 mg/kg and 1.0 mg/kg(P<0.05).The results showed that high content of nitrite in water had significant adverse effects on the growth,antioxidant and non-specific immune properties of E.sinensis,and the addition of selenium in the diets could help to improve the growth and immune properities and had a significant relief on the toxicity.3.Effects of astaxanthin and selenium on growth,osmotic pressure,antioxidant and non-specific immune performance of E.sinensis under high pH stressIn this study,astaxanthin and selenium were added to the basal diets,respectively,and the contents of astaxanthin and selenium were 0,0 mg/kg;120,0 mg/kg;0,0.9 mg/kg;and 120,0.9 mg/kg.The E.sinensis(3.26 ± 0.05 g)were cultured under the high pH(pH 9.5)stress taken the freshwater as the control group.After 8 weeks of feeding,we found that:(1)compared with the control group(pH 8 and fed on basal diet)the weight gain rate of the stressed group was lower but with no significant difference(P>0.05).The groups of astaxanthin or selenium addition had significantly higher weight gain rate while the group contained both astaxanthin and selenium had the lowest weight gain rate(P<0.05).Compared with the control group,the feed coefficient of the basal diet group under high pH was significantly higher than that of other groups(P<0.05).There was no significant difference among other groups(P>0.05).(2)Compared with the control group,the activity of Na+-K+-ATPase in the gill of the larvae of E.sinensis under high pH was significantly decreased(P<0.05),and the lowest in the basal diet group(P<0.05).Under the stress,the addition of astaxanthin and selenium was better than that of the non-adding group,but the effect of the addition of the two materials group was no better than that of the single additive group.The change of total amino acid under high pH stress was similar to that of Na+-K+-ATPase.(3)Compared with the control group,the activities of SOD in serum and hepatopancreas were significantly increased under high pH stress(P<0.05)and the highest levels of MDA appeared significantly than other groups(P<0.05).After adding astaxanthin and selenium,the MDA in the serum and hepatopancreas were significantly decreased(P<0.05),the GPX and T-AOC markabley increased(P<0.05).(4)The total number of blood cells was decreased and oxygen consumption rate was significantly increased(P<0.05)in stressed group.There were no significant difference between the group with additional astaxanthin and the control group.Compared with the control group,the lysozyme,acid phosphatase and alkaline phosphatase were significantly decreased(P<0.05)in the hepatopancreas of the crabs fed with the basal diet under high pH stress,and raised in the groups with diets supplemented with astaxanthin or selenium.However,the effects of adding astaxanthin and selenium were worse than adding signally.After culturing for 8 weeks,the crabs were treated with Aeromonas hydrophila.Compared with the control group,the mortality rate was significantly higher at 12 h after high pH stress,and the cumulative mortality rate was above 90%after 168 h which was significantly higher than the other groups.The results showed that high pH stress could have adverse effects on the growth performance,antioxidant capacity,osmotic pressure regulation and immunopathic resistance of the larvae of E.sinensis.The dietary supplementation of astaxanthin or selenium had a good effect on the antioxidate system,improve the activity of ACP and strengthen the non-specific immune resistance,but the effect of adding both at the same time is not ideal and it is not recommended to add astaxanthin and selenium at the same time.