| Since China broke through the artificial breeding technology of turbot in 1999,the annual output of turbot has been stable at about 50,000 tons after more than 20 years of development,and a large-scale breeding system and a relatively complete industrial chain have been gradually formed.The turbot has been popularized in Shandong Peninsula,Hebei and Liaodong Peninsula,and extended to the coastal areas of Zhejiang and Fujian.Factory circulating water is the main farmed mode,dissolved oxygen in water is an important environmental factors affect the growth of turbot survive,but not yet for turbot hypoxia tolerance physiological threshold definition and detail,the hypoxia tolerance ability has not been reported in detail,and the effect of hypoxia stress on its physiological function mechanism is not perfect.In this study,the hypoxic tolerance of turbot was determined.Through the acute hypoxic stress and recovery experiment,the changes of blood physiological and biochemical indexes of turbot were analyzed,the change rule of antioxidant enzyme activity in liver was found out,and the adaptability of turbot to low dissolved oxygen environment was discussed.The main results were as follows:1.When the Critical oxygen partial pressure(Pcrit)of female and juvenile turbot was 170 g,the dissolved oxygen concentrations were 3.34±0.23 mg/L and 3.22±0.17 mg/L,respectively.When the loss equilibrium(LOE)is out of equilibrium,the concentration of dissolved oxygen in water is 1.16±0.12 mg/L and 1.16±0.14 mg/L,respectively.There is no significant gender difference in tolerance to hypoxia.2.With the decrease of dissolved oxygen concentration in water,plasma cortisol,COR,glucose,Glu and red blood cell number(RBC)increased first and then decreased,and reached the maximum at LOE point(P<0.05).Mean corpuscular hemoglobin concentration,mean corpuscular hemoglobin concentration,mean corpuscular hemoglobin concentration,mean corpuscular hemoglobin concentration.MCHC was firstly decreased and then increased,and the lowest value was reached at Pcrit point(P<0.05).The concentrations of white blood cell(WBC),albumin(ALB)and globulin(GLB)increased first and then decreased,and reached the highest at Pcrit point(P<0.05).The contents of total cholesterol,triglyceride,high-density lipoprotein and low-density lipoprotein in serum were not significantly changed(P>0.05).The activity of superoxide dismutases(SOD)in liver firstly decreased and then increased.The content of Malondialdehyde(MDA)and the activity of catalases(CAT)increased firstly and then decreased.Glutathione peroxidase(GSH)activity did not change significantly.After returning to normal dissolved oxygen for 24 h,there was no significant difference between the above indexes and the control group(P>0.05),but the MCH content of male fish(P<0.05)and liver GSH activity were significantly increased(P<0.05).3.During 3 h of acute hypoxia(1.5±0.2 mg/L)stress,the COR of juvenile turbot maxima was increased,and reached the highest value at 3 h(P<0.05).Glu had no significant change(P>0.05).RBC,hemoglobin(HGB)and MCHC concentrations increased first and then decreased,and reached the highest values under 1 h of stress(P<0.05).Serum total cholesterol(TC)showed a decreasing trend,with the highest content in control group(P<0.05).Triglyceride(TG)and high-density lipoprotein(HDL)were increased firstly and then decreased,and reached the highest values at 1 h and 3 h,respectively(P<0.05).The low-density lipoprotein(LDL)content had no significant change(P>0.05).The WBC content of female fish was significantly increased,and reached the highest level at 3 h of stress(P<0.05),but there was no significant difference in the WBC content of male fish(P>0.05).ALB and GLB contents showed an increasing trend,and reached the highest value under 3 h stress(P<0.05).The activity of SOD in liver showed wavy change.MDA decreased in female fish,but no significant change in male fish.There was no significant change in GSH activity.CAT activity increased first and then decreased.After returning to normal dissolved oxygen for 12 h,there was no significant difference between the above indexes and the control group(P>0.05),and GLB was significantly increased in male fish(P<0.05).TC and LDL were significantly decreased(P<0.05);The MDA activity in liver of female fish was significantly decreased(P<0.05);CAT activity was significantly decreased(P<0.05).4.Under acute hypoxic stress(3.3±0.2 mg/L)for 6 h,the plasma COR concentration of juvenile turbot had no significant change(P>0.05);Glu content increased first and then decreased(P<0.05),and reached the highest value under 3 h of stress for female(P<0.05),and reached the highest value under 6 h of stress for male(P>0.05).RBC and MCH increased first and then decreased,and reached the highest value under 6 h stress(P<0.05).MCHC concentration showed a decreasing trend,and reached the lowest value under 6 h stress(P<0.05).TC showed a decreasing trend,and the content of TC in control group was the highest(P<0.05).There were no significant differences in triglyceride,high density lipoprotein and serum(P>0.05).LDL showed wavy changes,and reached the lowest level under 3 h stress(P<0.05).The contents of WBC,ALB and GLB tended to increase,and reached the highest value under 6 h stress(P<0.05).There was no significant difference in SOD activity in liver(P>0.05).MDA and GSH contents increased,and reached the highest under 6 h stress(P<0.05).CAT activity increased first and then decreased.After returning to normal dissolved oxygen for 12 h,there was no significant difference between the above indexes and the control group(P>0.05),and the MCHC of male fish was significantly decreased(P<0.05).TC and LDL were significantly decreased(P<0.05);The activities of MDA and GSH in liver of female fish were significantly increased(P<0.05).In summary,this study found that there was no significant gender difference in the hypoxic tolerance of turbot.Acute hypoxic stress resulted in significant changes in blood physiological and biochemical indexes and antioxidant enzyme activities in the liver,and the above indexes returned to normal levels after 12 h of normal dissolved oxygen.The results can provide theoretical basis and data support for precision culture of turbot and breeding of hypoxic tolerant varieties. |
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