Systemic infection in Atlantic salmon Salmo salar with a Dermocystidium-like species

A chronic mortality in subadult Atlantic salmon Salmo salar reared in California was caused by systemic infections with a Dermocystidium-like species. Parasitic cells occurred primarily at the periphery of granulomas in the kidney, liver, spleen and testes. Actively replicating vegetative stages 2 to 7 pm in diameter were also found withln melanomacrophages of the kidney. These stages contained a dense granular cytoplasm with osmiophilic inclusions, a nucleus with an indishnct nucleolus and were surrounded by thick, Periodic-Acld-Schiff-positive cell walls. The parasite induces a similar disease and has structural affinities to Dern~ocystidium spp. described as causes of systemic infections in salmonids in Europe.