Toxic Effects Of Copper And Cadmium To Early Life Stages Of Thamnaconus Septentrionalis

Heavy metal is a common water pollutant with strong toxicity,strong enrichment ability and not easy to be degraded.Heavy metal pollution in water has an important effect on various physiological processes such as reproduction and development of fish.Fish in the early life stage are especially sensitive to heavy metal content in the water environment.Exposure to heavy metals can prolong the development time of fish embryos,decrease the hatching rate of embryos,and increase the survival rate and deformity rate of larva and juvenile fish.Meanwhile,the enrichment of heavy metals in fish also poses a potential threat to human diet safety and health.Therefore,it is very important to explore the toxic effects of heavy metals on aquatic organisms.In this study,we selected copper（Cu）and cadmium（Cd）,two common heavy metal pollutants in water,to investigate the acute toxic effects of Cu and Cd on the early development stage（embryo,larva and juvenile）of the T.septentrionalis.The main research contents are as follows:1.Acute toxic effects:To study the acute toxic effects of Cu and Cd on embryos,larvae and juveniles of T.septentrionalis.The concentration gradients of formal tests were determined to be 0,0.02,0.07,0.12,0.17 mg/L;0,1,3,5,7 mg/L by static water test.The toxicity test of embryo in the early gastrulae and organogenesis stage were carried out.The concentration gradients of Cu²⁺and Cd²⁺were set as 0,0.03,0.08,0.13 and 0.18mg/L;0,2,4,6,8 mg/L,respectively to explore the acute toxic effects on newly hatched larva.The equal space between logarithm method was used to set four Cd²⁺concentration gradients（8.19,9.18,10.30,11.56 mg/L）and four Cu²⁺concentration gradients（1.10,1.35,1.67,2.05 mg/L）to investigate the acute toxic effects.The results showed as follows:（1）With the increase of heavy metal solution concentration,the embryo deformity rate of T.septentrionalis was increased,and the hatching rate was decreased.The development time of blastocyst to neurula stage,organ differentiation to membrane stage was first shortened and then extended with the increase of Cu²⁺concentration,and the development time of both stages was prolonged with the increase of Cd²⁺concentration.The mortality of Cu²⁺and Cd²⁺groups increased with the increase of Cu²⁺and Cd²⁺concentrations in the two developmental stages.Under the same concentration,the embryonic mortality from organ differentiation to membrane development stage was lower than that from blastocyst to neurula stage.（2）The newly hatched larvae showed various deformities such as V,S,L and U.The survival rate of hatchling larvae was inversely proportional to the concentration of heavy metal solution and incubation time,and the malformation rate was directly proportional to the concentration of heavy metal solution.The 72 h LC₅₀ values of Cu²⁺and Cd²⁺were 0.063 mg/L and 3.589 mg/L,respectively.The safe concentrations were 0.006 mg/L and 0.359 mg/L,respectively.（3）With the increase of Cu²⁺and Cd²⁺concentration and the prolongation of stress time,the poisoning symptoms of juvenile T.septentrionalis were similar but the degree of poisoning deepened.The LC₅₀ values of Cu²⁺and Cd²⁺for juvenile T.septentrionalis at 96 h were 1.14 mg/L and 9.19 mg/L,respectively.The safe concentrations were 0.11 mg/L and 0.92 mg/L,respectively.The results showed that Cu²⁺was more toxic than Cd²⁺to embryonic development,larvae and juveniles of T.septentrionalis,and Cu²⁺and Cd²⁺exposure of T.septentrionalis embryos were more sensitive than juveniles.2.Effects of Cu and Cd on antioxidant system and lipid peroxidation levels in liver of juvenile T.septentrionalis:According to the results of acute toxicity tests of Cu²⁺and Cd²⁺on juvenile T.septentrionalis,the concentrations were set as 0.15,0.35,0.55 and0.75 mg/L;0.92,1.84,2.76 and 3.68 mg/L,respectively.The contents of superoxide dismutase（SOD）,catalase（CAT）,glutathione antioxidant oxidase（GSH-PX）and malondialdehyde（MDA）in liver were detected at 6 h,12 h,24 h,48 h,72 h and 96 h,respectively.The results showed that compared with the control group,the activities of SOD,CAT and GSH-PX in Cu²⁺and Cd²⁺concentration groups were firstly increased and then decreased during 6-96 h.Compared with the control group,MDA content decreased first and then increased.3.Effects of Cu and Cd on liver and gill structure of juvenile T.septentrionalis:According to the results of acute toxicity tests of Cu²⁺and Cd²⁺,the concentrations were set as 0.15,0.35,0.55 and 0.75 mg/L;0.92,1.84,2.76 and 3.68 mg/L,respectively.The liver and gills were sampled at 24 h,48 h,72 h and 96 h.The results showed as follows:according to the results of acute toxicity tests,the concentrations were set as 0.15,0.35,0.55 and 0.75 mg/L;0.92,1.84,2.76 and 3.68 mg/L,respectively.liver and gill samples were taken at 24 h,48 h,72 h and 96 h,respectively.The results showed that with the increase of Cu²⁺and Cd²⁺concentration and the extension of the treatment time,the damage degree of liver and gill tissue structure of juvenile fish was deepened,and there was an obvious dosing and time effect relationship.The specific manifestations of liver tissue injury were:increased cell volume,irregular shape,blurred cell membrane boundary,blood vessel and hepatic sinuses congestion,vacuolation,etc.The specific manifestations of gill tissue injury are:curvature of gill lamella,edema and enlargement of epithelial cells,adhesion and fusion of adjacent gill lamella,cell necrosis and shedding,etc.