Abstract: To investigate the toxic effects of fuel oil on marine fishes,the juvenile Paralichthys olivaceus was exposed to low concentrations of 180CST fuel oil aqueous solution.The activities of superoxide dismutase (SOD),catalase (CAT),peroxidase (POD) and glutathione S-transferase (GST),and the malondialdehyde (MDA) content in liver and gill,as well as the lysosomal membrane stability (LMS)of hemocyte were measured.In addition,DNA damage was determined using the comet assay.Results indicated that,antioxidant enzyme activities and MDA contentin liver and gill of juvenile P.olivaceus had different responses to the stress of water-solution fraction in fuel oil.And activity of the single enzyme was also diverse at different time.Moreover,the LMS of hemocyte decreased significantly (P0.05) with increasing exposure time and concentrations of fuel oil.After a 6-day recovery period,the LMS in 0.001mg/L concentration group restored to the control level(P0.05),whereas they were still significantly lower (P0.05) in 0.010 mg/Land 0.100 mg/L concentration groups.A 15-day exposure period of fuel oil could cause moderate DNA damage in 0.001mg/L and 0.010 mg/L concentration groups,and serious DNA damage in 0.100 mg/L concentration group.However,after a 6-day recovery period,DNA damage has been recovered but still significantly higher(P0.01)than control level.In conclusion,fuel oil exposure promoted the level of lipid peroxidation,reduced LMS of juvenile P.olivaceus,and eventually led to genetic toxicity.