Surface disinfection of Atlantic halibut Hippoglossus hippoglossus eggs with ozonated sea-water inactivates nodavirus and increases survival of the larvae

Disinfection by ozonation of sea-water may reduce the risk of transmission of nodavirus, a major fish pathogen, via Atlantic halibut Hippoglossus hipp oglossus eggs. In the present study, eggs at 4 d prior to hatching were exp osed to nodavirus and then to ozonated sea-water using different concentrat ions (0.3 to 10 mg l(-1)) and exposure times (0.5 to 10 min). None of the l arvae from virus-exposed eggs washed with ozonated sea-water developed vira l encephalopathy and retinopathy (VER), which was detected in all dead larv ae from eggs exposed to nodavirus but not washed with ozonated seawater. In the non-treated control group about 20% of the dead larvae developed the d isease. This suggests that the halibut eggs taken from a large-scale produc tion facility were already contaminated with nodavirus. The egg groups whic h had been treated with 4 mg O-3 l(-1) for 0.5 min or with lower total ozon e exposures had a higher survival and no adverse effects on the development of the larvae after hatching were observed. Although a slight delay in hat ching was found, after 2 d the cumulative hatching had normalised. In the e gg groups with high total exposure (4 mg O-3 l(-1) for 1 min or higher tota l ozone exposures) a pronounced negative effect on hatching was observed. O ur results indicate that the egg surface may be important in the transfer o f nodavirus and that nodavirus associated with the surface of the egg may b e inactivated by ozonated sea-water.