Parasites of the genus Dermocystidium found in Atlantic salmon (Salmo salar) and brook trout (Salvelinus fontinalis) farmed in eastern Canada

Dermocystidium parasites cause disease and infection among important aquacultural species of finfish, including Atlantic salmon, Salmo salar, chinook salmon, Oncorhynchus tshawytscha, rainbow trout, Oncorhynchus mykiss and brown trout, Salmo trutta.

A study was undertaken to compare the endogenous stages of Dermocystidium spp. from Atlantic salmon and brook trout. With light microscopy, Dermocystidium organisms from both hosts, were round to oval in shape and varied in staining density. Ultrastructurally, five phases of the endogenous stages were observed in Atlantic salmon tissues: immature and mature trophozoites, and uninucleated, dividing and releasing schizonts. In brook trout, cysts of Dermocystidium sp. contained only mature trophozoites and uninucleated schizonts. Mature trophozoites from both Dermocystidium spp. were characterized by the signet ring configuration, in which the nucleus is displaced against the parasite wall by a large vacuole. Schizonts were larger than the trophozoites and possessed more organelles: concentric bodies, lipoid bodies, electron-dense inclusions, mitochondria and vacuoles. (Abstract shortened by UMI.).