Dermocystidium-like parasite in farmed Atlantic salmon

Visceral and systemic infection with a Dermocystidium -like organism was diagnosed recently in post-seawater entry smolts of Atlantic salmon farmed in the Bay of Fundy. In late summer and early fall, young fish developed "black smolt" disease, characterized by anorexia, lethargy and black skin. Parasites were evident histologically in various tissues, including cardiac muscle, liver, spleen, brain and gills, and were associated with inflammation, including formation of granulomas. Small (3-7 mu m diameter) parasites developed in melanin-containing macrophages. Market-weight fish also developed disease that was noticeable in mid winter; grossly visible granulomas developed in kidney and liver.