ISOLATION OF AN IRIDOVIRUS FROM PIKE-PERCH STIZOSTEDION-LUCIOPERCA

We have isolated a large virus from pike-perch Stizostedion lucioperca fingerlings with no signs of disease. The biochemical, structural, an d serological properties of this newly isolated virus suggest that it belongs to the family Iridoviridae. The virus multiplied and was cytop athogenic in several cultured fish cell lines. The virus has a DNA-con taining genome and is assembled in the cytoplasm. When viewed in elect ron micrographs, the assembly sites showed a paracrystalline array of hexagonal nucleocapsids. The ultrastructure of the pike-perch virus re sembled that of previously isolated fish iridoviruses. It is an envelo ped icosahedral DNA virus. The diameter of the nucleocapsid in thin se ctions was 127 +/- 3 nm; in negatively stained preparates the size of the enveloped virus varied from 147 to 187 nm. In immunofluorescence t he virus was stained by rabbit antisera against EHN (epizootic haemato poietic necrosis) virus, sheatfish iridovirus and cod iridovirus. The pathogenicity of the virus isolate was studied by inoculation into juv enile rainbow trout Oncorhyncus mykiss. Experimental infection under a quarium conditions suggested that the virus is apathogenic to rainbow trout. The infective virus could be recovered from the viscera of inoc ulated fish during the first week post-infection, after which the prop ortion of virus-positive fish declined over time. A small proportion o f the fish still carried the virus 24 d post-inoculation.