Effect of heavy metal stressors and salinity shock on the susceptibility of grouper (Epinephelus sp.) to infectious pancreatic necrosis virus

In the present study, attempts were made to clarify the effect of heavy met al stressors and salinity shock on the disease susceptibility of grouper fr y (Epinephelus sp.) to infetious pancreatic necrosis virus (IPNV) infection . Zinc, cadmium and copper (5 ppm ZnCl2, 3 ppm CdCl2 and 1 ppm CuCl2) were used to treat groupers before and after virus infection. Cumulative mortali ties in the experimental groups were 96-100% within 42 days. Only 5-15% mor talities were observed in most of the groups that were exposed to either he avy metals or virus infection alone. Subsequently, virus was re-isolated fr om the experimentally infected groupers, and copper concentration was measu red in fish that had been exposed to CuCl2. We also investigated the effect of salinity shock (i.e. an abrupt change of salinity level from 33 ppt to either 40 ppt or 20 ppt) on susceptibility of grouper to IPNV. Similar resu lts were obtained, mortalities of groupers in the experimental groups reach ed 80-100%. The results of the present study suggest that an IPN virus with only low pathogenicity could cause high mortality in groupers when combine d with environmental stress. (C) 1999 Elsevier Science B.V. All rights rese rved.