| As the most important breeding species of Siniperca,mandarin fish has prominent nutritional and health value.In the last century,mandarin fish was cultivated artificially in China.Nowadays,a complete set of breeding techniques has been formed,including germplasm protection,breeding of improved varieties,fry breeding and cultivation.In the process of high density intensive farming,the high concentration of ammonia nitrogen in aquaculture water often exerts stress on the fish.Once improperly controlled,it will cause unavoidable losses to production.In this study,the physiological responses of juvenile mandarin fish to ammonia-nitrogen stress were studied through the changes of antioxidant and non-specific immune indices.1.Acute toxicity of ammonia nitrogen to juvenile mandarin fish was studied with 0,30,60 and 90 mg/L concentration gradient groups.The results showed that the total ammonia nitrogen LC50 for 96h and non-ionic ammonia LC50 for 96h were 48.65 mg/L and 0.47 mg/L respectively.According to the formula of safe concentration(SC),the safe concentration of total ammonia nitrogen and non-ionic ammonia were 4.865 mg/L and 0.047 mg/L,respectively.With the increase of ammonia nitrogen concentration,the mortality of juvenile mandarin fish increased rapidly.The mortality of juvenile mandarin fish in the 90 mg/L experimental group reached 97%at 96 h.That is to say,the survival rate of juvenile mandarin fish was negatively correlated with ammonia nitrogen concentration.2.In this study,the concentration of total ammonia nitrogen 96h LC50 was set as the experimental concentration,and the gill tissues were sampled at 0,6,12,24,48 and 96 hours for the determination of ionase and antioxidant index.The results showed the activity of ionase in gill tissue of juvenile mandarin fish showed a decreasing-increasing-decreasing trend within 96 hours.At 48 hours,the activity of ionase was significantly higher than that at 0 hours(P<0.05),and at 96 hours,the activity of ionase was significantly lower than that at 48 hours(P<0.05).The activities of catalase and reduced glutathione in gill tissues of juvenile mandarin fish showed a trend of increase-decrease.The activities of catalase and reduced glutathione at 24 hours were significantly higher than those at 0 hours(P<0.05),and decreased significantly within 48-96 hours(P<0.05).The activities of superoxide dismutase and peroxidase in gill tissue of juvenile mandarin fish showed a downward-upward-downward trend within 48 hours,but there was no significant difference between 48 and 96 hours(P>0.05),while the activities of peroxidase were significantly different during that time(P<0.05).The results showed that in the short-term acute ammonia-nitrogen toxicity test,the ionase and antioxidant related indexes in gill tissue of juvenile mandarin fish increased first and then decreased,which had a significant impact on its antioxidant function.In the process of aquaculture,attention should be paid to the change of ammonia nitrogen in water to reduce the impact of ammonia nitrogen on fish growth.3.The total ammonia nitrogen concentration of 96h LC50 was set as the experimental concentration,and the time gradient was used to sample the juvenile mandarin fish at 0,6,12,24,48 and 96 hours.The activity of immune-related enzymes and gene expression were measured in the head kidney tissue of juvenile mandarin fish.The results showed that the activities of catalase,alkaline phosphatase and acid phosphatase in the head kidney of juvenile mandarin fish increased first and then decreased.At 48 h of ammonia nitrogen stress,the activities of three enzymes were significantly higher than those at 0 h(P<0.05),catalase and acid phosphatase activities decreased significantly at 48-96 h(P>0.05),while at 96 h,the activities of alkaline phosphatase decreased slightly compared with those at 48 h(P>0.05),but there was no significant difference(P>0.05).The expression of IRF-1 gene in head kidney of juvenile mandarin fish decreased first and then increased.The expression of IRF-1 gene in head kidney of juvenile mandarin fish at 96 h was significantly higher than that at 0 h(P<0.05);the expression of IL-1 beta gene in head kidney of juvenile mandarin fish at 24 h was significantly higher than that at 0 h(P<0.05);the expression of IL-8 gene in head kidney of juvenile mandarin fish was significantly lower than that at 0 h(P<0.05).Trend:The expression of IL-8 gene at 96 h was significantly lower than that at 0 h(P<0.05).The results showed that in the short-term acute ammonia nitrogen toxicity test,the activity of immune-related enzymes in head kidney of juvenile mandarin fish increased first and then decreased.The expression level of immune-related genes was lower than 0 h at 96 h.It was known that ammonia nitrogen stress had an impact on the immune function of juvenile mandarin fish.In the process of aquaculture,attention should be paid to the change of ammonia nitrogen in water.Excessive concentration of ammonia nitrogen affects the normal immune function of fish,which is vulnerable to the threat of diseases and causes huge losses to production. |
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