In ultrathin sections of virus-infected GP
cells, the matured virus particles usually showed
an hexagonal outline shape revealing that the
virus had an icosahedral structure. This observation
confirmed that the grouper iridovirus was
similar morphologically to that of another iridoviruses
(Berthiaume et al., 1984; Heppell and
Berthiaume, 1992) and African swine fever virus
(ASFV) (Carrascosa et al., 1984). The extracellular
virus particles had an external envelope which
derived from host plasma membranes. After negatively
stained with PTA, the newly forming
unfixed virons showed a well-defined hexagonal
outline and exhibited three electron-dense layers.
Previous studies showed that iridoviruses had an
external lipoprotein envelope, an inner periodic