Ozone(O₃)was frequently used in water treatment for industrial aquiculture.Therefore,in order to understand the impacts to ozone on aquiculture species Oplegnathus fasciatus,acute exposure of ozone on juvenile was conducted using self-designed ozone toxicity experimental set-up(authorized Patent Number:ZL 200920122441.3)with various exposure doses(0,0.08,0.13,0.17,0.22,0.28 and 0.32 mg/L)and durations(0.5,1,6,12,18 and 24 h).The impacts of ozone on behavioral responses,mortality,gill histomorphology,and antioxidant enzyme activities were investigated in present study.The results showed the distribution of juvenile O.fasciatus tends to move up to upper layer with increasing ozone exposure doses,in the meanwhile,the respiration rate was sped up and the startle response was slowed down.Moreover,evident dose-response relationship was found between mortality and ozone concentration.The regression equations between mortality and ozone dose at 12 and 24 hours were Y=16.815 8+20.340 5X(r=0.998 7)and Y=17.614 1+17.898 3X(r=0.950 0),respectively.The halflethal concentration(LD₅₀)at 12 and 24 hours were 0.262 5 and 0.197 4 mg/L,respectively.Compared to control,with the increase of ozone exposure dose and duration,the activities of superoxide dismutase(SOD)and glutathione peroxdase(GPX)in gills of juvenile O.fasciatus were downgraded,while the quantity of malonaldehyde(MDA)was upgraded in experimental trials.Under ozone exposure stress,the gill lamella of juvenile O.fasciatus was shown to be in irregular array and some necrosis phenomenon was detected.Shedding epithelial cells from gill lamella were also observed.The vessel of gill filaments was pycnosis or even became cavum.The vessel wall was found to be rough and shrunk,with pyknotic and necrotic blood cells attached.