Epitheliocystis disease in the striped bass Morone saxatilis from the Chesapeake Bay.

Epitheliocystis disease in the gills of the striped bass Morone saxatilis from Chesapeake Bay was studied using light and electron microscopy. The epitheliocystis infection appeared synchronous in that all capsules on a single host were at the same stage of development. The disease appeared to begin in a single cell on the gill lamella, which gradually enlarged to form a large cyst, encapsulated by a thick cellular capsule of epithelial origin. The epitheliocystis inclusion was filled with cells of the general morphology and size of rickettsiae; however, the infection was atypical for rickettsiae in that the cells had a dense central nucleoid region and they developed within an inclusion separated from the host cytoplasm.