Effect Of Cu Stress On Respiratory Metabolism,Digestive Enzyme And Antioxidation Function Of Juvenile Aplodinotus Grunniens

Aplodinotus grunniens is commonly known as freshwater drum,or sheepshead,native to the American and widely distributed in freshwater systems from southern Canada to Guatemala.It is the most widely distributed warm-water fish in North America,and also one of the only 275 species of Sciaenidae in the world that live in freshwater throughout their lives.With the development of industry,agriculture and other undertakings,a large amount of herbicides and heavy metal ions were discharged during their production or experiments,which has caused pollution to the environment,especially the water bodies.In view of the good farming prospects and economic value of freshwater drum,the toxicological methods were used in this study to determine the semi-lethal concentration and safe concentration of copper in freshwater drum juveniles,and to study the effects of acute copper stress on the respiration metabolism,digestive and anti-oxidation indexes of the main tissues and organs of the freshwater drum juveniles,which were designed to provide basic data for the toxicology research of freshwater drum.The influencing mechanism of acute copper stress on antioxidant of the freshwater drum juvenile provides a reference for the safe use of copper-containing aquatic drugs and healthy aquaculture management in the process of freshwater drum culture.The relevant research results are as follows:（1）The experimental results of the acute toxicity of copper ions to the juvenile of freshwater drum showed that when the concentration of Cu was 0.100,0.197,0.387,0.762,and 1.5 mg/L,the mortality rate of 96h was 15.55±3.85%,17.78±3.85%,93.33±6.67%,100.00±0.00%,100.00±0.00%respectively.The LC₅₀of Cu on freshwater drum at 24 h,96 h was 0.313 mg/L,0.291mg/L,and the safe concentration was 0.029 mg/L.The safe concentration of Cu in freshwater drum juvenile is significantly lower than the 0.263 mg/L safe concentration of Japanese yellow crocker juvenile,the safe concentration of Chinese sea bass juvenile 0.086 mg/L and the safe concentration of carp 0.077 mg/L.According to the toxicity classification standard and the test results,it is shown that freshwater drum has a poor tolerance to copper,which has important theoretical guidance value for the safe use of copper-containing preparations in freshwater drum culture.（2）Under the conditions of water temperature of 15℃and 20℃,the experiment of the effect of copper ions on the oxygen consumption rate and ammonia excretion rate of freshwater drum juveniles was carried out.And the results showed that temperature had a significant effect on the oxygen consumption rate and ammonia excretion rate of freshwater drum（P<0.01）,in the temperature range of 15-20℃,the oxygen consumption rate and ammonia excretion rate increase with the increase of temperature,indicating that increasing the temperature can promote the level of respiration and metabolism of freshwater drum juvenile.The effect of Cu concentration on the oxygen consumption rate is not significant（P>0.05）.The oxygen consumption rate increases with the increase of Cu concentration at15℃,and the oxygen consumption rate first increases and then decreases with the increase of Cu concentration at 20℃.The concentration of Cu has a significant effect on the ammonia excretion rate（P<0.05）.The ammonia excretion rate first increases and then decreases with the increase of Cu concentration at 15℃,and decreases with the increase of Cu concentration at 20℃.The synergistic effect of temperature and Cu concentration has no significant difference in oxygen consumption rate（P>0.05）,but has a significant difference in ammonia excretion rate（P<0.05）.With the increase of temperature,the copper ions has much significant effect to juvenile of freshwater drum.（3）Based on the results of the toxicity test,the effects of acute copper stress on the digestive and antioxidant functions of freshwater drum juveniles were further studied.And the results showed that the activities of Na⁺-K⁺-ATPase,α-AMS,Lipase,PP,T-AOC,and Na⁺-K⁺-ATPase,α-AMS,Lipase,PP,T-AOC,GPx,GSH,SOD enzymes and cortisol were significantly higher than those of the control group at 4h（P<0.05）under the stress of 0.197mg/L Cu,while there was no significant difference at 12h（P>0.05）.The results indicated that Cu stress would cause these 9 biochemical indexes to rise in a short period of time and then fall under the regulation of physiological mechanisms.In the period of 1 d～4 d,the activities of these 9 biochemical indexes decreased to different levels,indicating that Cu had different of toxic effects on the gill,liver and intestines of the fish.Cu stress causes the most serious damage to the gill,and has a greater impact on the Na⁺-K⁺-ATPase enzyme activity on the gill.Cu stress also has a serious impact to the liver,of which the SOD enzyme has the most serious impact,and the CAT enzyme activity is less affected.The results indicate the CAT enzyme was significantly higher than the control group in second day（P<0.05）,while no significant difference in the other periods（P>0.05）.Cu stress causes greater damage to the liver,mainly leading to a significant increase in liver ALT,AST and MDA content（P<0.05）,and MDA is more sensitive to Cu stress than ALT and AST.Compared with the damage to the gill and liver,Cu stress has less damage to the intestinal tract.Among them,it has the greatest impact on PP activity,followed byα-AMS,and it has the least impact on Lipase activity.Comprehensive analysis showed that the acute stress of copper caused varying degrees of damage to the respiration metabolism,digestive and antioxidant functions of the main metabolic organs of freshwater drum juvenile.Among them,the respiratory metabolism was the most significantly affected,followed by the liver,and the least impact was the digestive tract.