The morphogenesis and the ultrastructure of a marine fish iridovirus isolated from diseased grouper, Epinephelus
tauina were studied by electron microscopy. The virus was grown on a marine fish cell line (GP) at 25 °C. After
appearance of advanced cytopathic effect (CPE), various morphogenetic stages of virus amplification, maturation and
assembly were detected in the cytoplasm of virus-infected cells. The matured nucleocapsids were probably formed by
insertion of electron-dense core material into a partly forming empty capsid just before completely sealed. The
nucleocapsids were located at the assembly sites as pseudocrystalline arrays or scattered individually. In the late phase
of infection, the nucleocapsids were enveloped and released by budding from the plasma membrane. The budding
virus particles could directly enter neighbouring cells by endocytosis to start the next round infection. Ultrastructure
of the grouper iridovirus was studied using the methods of enzymatic digestions and detergent degradations. The
purified iridovirus particles showed a three-layered membrane including an external lipoprotein envelope, an inner
periodic protein capsid and a lipid-containing membrane. The regular array of surface capsid subunits was observed
after degradation with detergent. © 2001 Elsevier Science B.V. All rights reserved.