Effects Of Dissolved Oxygen Levels On Respiratory Metabolism,Physiology,Biochemistry And Tissue Structure Of Cynoglossus Semilaevis

In this paper,we investigated the changes in respiration rate of Cynoglossus semilaevis at four dissolved oxygen gradients of 3 mg/L,8 mg/L(control),14 mg/L and 20 mg/L at different times(3 h,1 d,7 d and 14 d)and changes on respiratory metabolism,tissue structure and physiological and biochemical indices after 14 days of the test.It was found that by the time of 3 hand 1 d the respiratory rate increased in the low oxygen group(3 mg/L)while the respiratory rate decreased in the high oxygen group(14mg/L and 20 mg/L),and the difference was significant(P<0.05)compared to the control group,and the respiratory amplitude(gill cover opening and closing)was smaller in the high oxygen group,and after 1 d,the respiratory rate was accelerated in all groups.After 7 d of culture,there was no significant difference(P>0.05)between the low oxygen group and the control group(8 mg/L),and the respiratory rate was low in the 14 mg/L and 20 mg/L groups,which were significantly different from the control group(P<0.05).after 14 d of culture,the respiratory rate increased in the 3 mg/L and 8 mg/L groups,but the difference between the two groups was not significant(P>0.05).the respiratory rate decreased in the 14 mg/L and There was no significant change in respiratory rate in the 20 mg/L group,and the amplitude of gill cover opening and closing did not change significantly during the test period.The oxygen consumption rate of Cynoglossus semilaevis also decreased significantly(P<0.05)and the ammonia excretion rate increased but not significantly(P>0.05)under hypoxic stress(3 mg/L),probably because its metabolism started to change gradually from aerobic to anaerobic in order to counteract hypoxic stress and reduce oxygen consumption.14mg/L The rate of oxygen consumption in the test group was higher than that in the control group,but there was no significant difference(P>0.05),but the rate of ammonia excretion was significantly higher(P<0.05),and the above phenomenon was also observed in the test group at 20 mg/L.The RBC and HGB in the blood of the test fish in the 3 mg/L group were increased compared with the control group(P>0.05),and the HCT content was reduced compared with the control group(P>0.05).The RBC,HGB and HCT indexes of the test fish in the 14 mg/L and 20 mg/L groups were higher than those of the control group(P>0.05).The MDA content,SOD activity and CAT activity in the measured serum were significantly higher than those in the control group(P < 0.05).It indicates that both hypoxia and hyperoxia cause oxidative damage to Cynoglossus semilaevis.Both hypoxia or hyperoxia resulted in epithelial cell layer proliferation in gill tissue,and vacuolation was more common in gill tissue of Cynoglossus semilaevis under hyperoxia.Liver sections of the hypoxic group showed obvious histological abnormalities compared to the control group,and the hepatocytes were extensively sparsely edematous with unclear cell outlines,while 14 mg/L and 20 mg/L revealed clear hepatocyte outlines,red stained cytoplasm,and no obvious degeneration.The experimental results can show that the fish will be damaged to different degrees regardless of the low and high oxygen conditions.The purpose of this study was to understand the broader effects of dissolved oxygen variation on Cynoglossus semilaevis,to help develop effective aquaculture practices,to better reduce costs,to optimize growth and health of this species,to provide information for precise control of dissolved oxygen in Cynoglossus semilaevis factory farming,and to help reveal the mechanisms of oxygen adaptation in Cynoglossus semilaevis.