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Ozone is a powerful oxidant which can be use for bacterial inactivation, deodorizing, and bleaching. In aquatic farms, it can improve larvae hatching and keep water quality under control. The primary object of this research is to investigate the influence of ozone solubility by the concentrations chloride¡]Cl-¡^and bromide¡]Br-¡^in seawater. The indigo colorimetric method was used to detect the variation of total residual oxidants¡]TROs¡^after ozonation. The bacteriocidal effects of ozone with added Cl- or Br- were tested on three common marine fish pathogens. The results showed that the ozone solubility in reverse osmosis¡]RO¡^treated water was about 2.3 mg/L, and rapidly decreased to 0.5 mg/L when ozonation stopped. The process of ozonation in seawater from start to equilibrium, the TROs concentration could reach 8.5 mg/L and then decreased slowly to a stable concentration of about 6 mg/L. When Cl- was added in RO water, the TROs concentration varied from 2 to 3.5 mg/L, and rapidly disappeared after stop ozonation. It was concluded that Cl- could not effectively increase ozone solubility in seawater. In contrast, adding Br- in RO water not only efficiently increased the solubility of ozone but also maintained the TROs concentrations after stop ozonation, and the TROs concentrations were proportional to the Br- concentrations. The same trends were also observed in seawater added with Br-. In the bacteriocidal effect of ozone, compare with pure seawater, adding of Br- in seawater could effectively reduce the TROs concentrations needed to completely inhibit each pathogen. Such practice may be extended to aquatic farms to eliminate or reduce the bacterial pathogens in seawater.