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

Abstract

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 were also found within melanomacrophages of the kidney. These stages contained a dense granular cytoplasm with osmiophilic inclusions, a nucleus with an indistinct nucleolus and were surrounded by thick, Periodic-Acid-Schiff-positive cell walls. The parasite induces a similar disease and has structural affinities to Dermocystidium spp. described as causes of systemic infections in salmonids in Europe.