August 2014 Case of the Month

Muscle cyst in a Chinook Salmon

Case information

Eight large adult Chinook salmon (Oncorhynchus tshawytscha) presented to the Fish Disease Control Unit at Cornell University, captured by the Salmon River Fish Hatchery (Altmar, New York, USA) and the New York State Department of Environmental Conservation from Lake Ontario, during the spawning season (October to December) over a several year period. Large individual fluid-filled cavities were noted at necropsy in the skeletal muscle of the caudolateral body wall. Cysts ranged in size from 70-100 mm long x 40-60 mm wide x 20-30 mm deep. The fluid was slightly turbid, yellow to yellow-brown and odorless with scattered fragments of fibrin. Firm mottled granulation tissue surrounded the cavities. Fluid from the cavities were aspirated and submitted for cytologic examination. Sediment smears were prepared from the aspirated fluid.

View the following photomicrographs and answer these questions:

  1. What disease process is evident in the aspirate from the cyst (i.e. inflammation, neoplasia)?
  2. Is a cause identified?

August2014_Figure 1
Fig 1. Fluid from cyst (500x)

August2014_Figure 2
Fig 2. Fluid from cyst (1000x)

Answer on next page.

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