INACTIVATION OF BACTERIAL AND VIRAL FISH PATHOGENS BY OZONATION OR UVIRRADIATION IN WATER OF DIFFERENT SALINITY

Bacterial and viral fish pathogens were exposed to ozone or ultraviole t (UV) irradiation in laboratory batch systems. Inactivation curves we re made for Aeromonas salmonicida subsp. salmonicida, Vibrio anguillar um, Vibrio salmonicida, Yersinia ruckeri and the infectious pancreatic necrosis virus (IPNV) in ozonated lake, brackish and sea water at 9-1 2-degrees-C. The four bacteria tested were inactivated by 99.99% (4 lo g reductions in viable count) in all three waters within 180s at resid ual ozone concentrations of 0.15-0.20 mg/liter measured by the indigo colorimetric method. After establishing these residuals, the differenc es in water salinity did not cause any substantial differences in bact ericidal activity of ozone, illustrating the usefulness of concentrati on measurements by the indigo colorimetric method to predict inactivat ion also in saline waters. The rate of bacterial inactivation was fast during the first 60 s in all three waters. After that point the slope of the curves levelled off. This observation was explained by loss of ozone and reduced bactericidal activity during the course of the expe riments. IPNV was inactivated (99.99%) in all three waters within 60 s when exposed to 0.10-0.20 mg/liter residual ozone.V. anguillarum, V. salmonicida, Y. ruckeri and IPNV were UV irradiated in brackish water at room temperature. An UV dose of 2.7 mWs/cm2 resulted in 99.999% (5 log) reduction in viable count for all three bacteria. IPNV was much m ore resistant to irradiation than the bacteria. An average UV dose of 122 mWs/cm2 was required for 99.9% (3 log) reduction in virus titer.