| Marbled eel(Anguilla marmorata)is rich in resources and inexpensive,showing a great potential for breeding fish.However,low survival rate of marbled eel in the seedling cultivation process,slow growth,and intolerant low temperature seriously affect its nationwide promotion.Therefore,this paper studied the tolerance of marbled eel to temperature and commonly used drugs,and the results and conclusions are as follows:1.The semi-lethal low temperature in different cooling rates,oxygen consumption rate and asphyxiation point of juvenile marbled eel with different temperature and body weight were measured using artificial cooling method.The results showed that the LT50 of juvenile marbled eel were 7.23?,5.35?,4.95? and3.86? at the temperature-decreased speeds of 1?/1 h,1?/3 h,1?/6 h and 1?/12 h,showing an decreasing trend as the speed decreasing.The oxygen consumption rate of juvenile marbled eel decreased significantly(P<0.05)as body weight increased and the average asphyxiation point was(0.44±0.04)mg/L at water temperature of 30?.It was found that the relationship between oxygen consumption rate and body weight followed an exponential function law described as y = 0.681x-0.30(R2=1).The oxygen consumption rate and asphyxiation point of juvenile marbled eel with body weight of(7.70±0.73)g increased with increasing water temperature from 15? to 30?.There was significant difference(P<0.05)between oxygen consumption rates of different temperature.The relationship between oxygen consumption rate and temperature can be described as y = 0.110x-0.043(R2=0.996).The asphyxiation points of juvenile marbled eel were(0.34±0.01)mg/L,(0.35±0.02)mg/L,(0.39±0.01)mg/L and(0.44±0.01)mg/L when the water temperature from 15? to 30?,respectively.2.To investigate the effect of low acute temperature stress on serum biochemical indexes in juvenile marbled eel,an experiment was conducted in fourtemperature treatments(15,20,25 and 30?;the latter as control)and maintained for 7days.The results showed that significant difference(P < 0.05)in concentrations of glucose(GLU),total cholesterol(TC)and creatinine(CERA)in serum between 15?group and 30? group at 0 day and 7 days.The concentrations of CERA in 20? and25 ? were significantly(P < 0.05)higher than the control while the others serum biochemical indexes showed insignificant difference(P>0.05)with control at 7 days.The activities of alanine transaminase(ALT)in 15? and 20? were significantly higher(P<0.05)than the control at 0 day and decreased at 7 days.The activities of alkaline phosphatase(ALP)showed insignificant difference(P>0.05)with control at0 d but significantly higher(P < 0.05)at 7 days.The activities of aspartate transaminase(AST)and ALP in 15? and 20 ? significantly higher(P<0.05)than the control at 0 day and 7days.The results indicated that low acute temperature stress damaged the kidney,liver and heart of juvenile marbled eel.3.The effects of low acute temperature stress on antioxidant enzyme activities in liver of juvenile marbled eel were investigated in four temperature treatments(15,20,25 and 30?;the latter as control).The results showed that the activities of catalase(CAT)and glutathione peroxidase(GSH-Px)had insignificant difference(P > 0.05)with the control at 0 d,but significantly higher(P<0.05)than the control and also increased significantly with the increase of stress strength at 7 days.There was no significantly difference(P>0.05)in the activities of superoxide dismutase(SOD)and total antioxidant capacity(T-AOC)in all the treatments in 7 days.The concentrations of Malondialdehyde(MDA)in 15,20 and 25? were higher than the control at 0 day and decreased in 7 days,while only significantly higher than the control in 20?.The results indicated that low acute temperature stress led to more MDA to juvenile marbled eel and increased the activities of antioxidant enzyme.But the results that the activities of CAT and GSH-Px of 15,20 and 25?were higher than the control at the end of the experiment indicated that juvenile marbled eel can't adapt to low acute temperature stress.4.The acute toxicity of potassium permanganate,formaldehyde,sodium chloride and chlorine dioxide to juvenile marbled eel with body weight of(0.16±0.07)g were studied at water temperature of 27-29 ? using a static bioassay test.The results showed that the static acute 24 h LC50 of juvenile marbled eel was 4.45 mg/L inpotassium permanganate,104.74 mg/L in formaldehyde,27392 mg/L in sodium chloride and 3.74 mg/L in chlorine dioxide;the 48 h LC50 were 3.66 mg/L in potassium permanganate,93.75 mg/L in formaldehyde,25461 mg/L in sodium chloride and 2.76mg/L in chlorine dioxide;the 72 h LC50 were 3.46 mg/L in potassium permanganate,89.95 mg/L in formaldehyde,23699 mg/L in sodium chloride and 2.60 mg/L in chlorine dioxide;the 96 h LC50 were 3.31 mg/L in potassium permanganate,88.78mg/L in formaldehyde,22278 mg/L in sodium chloride and 2.44 mg/L in chlorine dioxide,with safe concentration(SC)of 0.74 mg/L in potassium permanganate,22.54mg/L in formaldehyde,6600 mg/L in sodium chloride and 0.45 mg/L in chlorine dioxide.The order of susceptibility of the juveniles to four medicines was expressed as chlorine dioxide > potassium permanganate > formaldehyde > sodium chloride.The findings indicate that potassium permanganate and formaldehyde should be used cautiously in common concentration,while sodium chloride and chlorine dioxide can be used safely.Chlorine dioxide has a strong lethal effect on juvenile marbled eel although the safety concentration was much higher than the concentration recommended by the disinfectant manufacture. |
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