The electron micrographs of negatively stained purified grouper iridoviruses showed a three-layered
membrane structure with an inner electrondense core surrounded by a light area (Fig. 6A).
In order to determine the inner fine structure, the central electron-dense core of the virons was
becoming loose (Fig. 6D). SDS had stronger degrading effects on the capsid of the virons. The structure of the viral capsid was markedly damaged after treatment with 1% w/v SDS for 5 min. The capsid subunits could not be visualised, and no organised structure was observable within the central core (Fig. 6E). The virons deteriorated significantly after treatment with 1% SDS for 7 min. The capsid membranes were explosive to be cotton-like materials surrounding the central core (Fig. 6F).