Plasmacytoid leukemia in seawater reared Chinook salmon Oncorhynchus tshawytscha

Abstract

A plasmacytoid leukemia was observed in chinook salmon Oncorhynchus tshawytscha reared in seawater netpens in British Columbia, Canada. The disease was first observed in market-size salmon (2 to 4 kg) and caused high mortality at several facilities. The disease, referred to as marine anemia by fish farmers, is characterized by pallor of the gills due to anemia, enlargement of the spleen and kidney, and ascites. Electron microscopy and immunohistochemistry revealed the plasmacytoid features of the proliferating cells. The cells contained a well organized, rough endoplasmic reticulum, the cisternae being distended with a lightly granular material. Immunoglobulin was detected in the cells in tissue sections with a goat antitrout immunoglobulin peroxidase stain. Although an infectious etiology (e.g. oncogenic virus) for the disease was suspected, no viruses have yet been detected by cell culture or electron microscopy.