Spores of three myxozoans of salmonids. Bar = 5µm. PC = polar capsule. A) Henneguya salminicola from salmon muscle. B) Myxobolus cerebralis from cartilage of salmon, the cause of whirling disease. C) Kudoa thyrsites from muscle, a myxozoan that infects many marine fishes and causes post-harvest degeneration of the flesh. Myxozoans, once thought to be protozoa, are metazoans (multicellular organisms) more closely related to the Cnidaria (jellyfish and relatives).
(Download full resolution TIFF image, 1.0 megabytes)

  Whirling disease in trout, caused by Myxobolus cerebralis. Note scoliotic vertebral column of fish. This myxozoan is thought to have been imported to the United States from Europe, and is a serious cause of disease in wild rainbow trout in the Rocky Mountain region. (Download full resolution TIFF image, 0.1 megabytes)

  Atlantic salmon held on ice for 3 days with destroyed muscle due to Kudoa thyrsites infection.
(Download full resolution TIFF image, 0.6 megabytes)

  The life cycle of Ceratomyxa shasta. Most myxozoans require development in an alternate annelid worm host to complete their life cycle. Usually this is an oligochaete, but C. shasta uses a freshwater polychaete. Certamyxa shasta causes disease in wild and captive salmon in freshwater. (Download full resolution TIFF image, 0.3 megabytes)

  Proliferative kidney disease (PKD) (A), characterized by a swollen kidney and spleen, bloody asictes (fluid in the visceral cavity), and pale gills (which indicate anemia). Note that these signs occur with many systemic diseases of fish. PKD is caused by the PKX parasite (B), a prespore stage of the myxozoan Tetracapsula byrosalmonae (= T. renicola) that infects the kidney, spleen and other organs. PKX cells (X) are surrounded by inflammatory cells in the kidney interstitium. Instead of annelid worms, this myxozoan uses bryozoans in its life cycle. (Download full resolution TIFF image, 3.1 megabytes)

  Nucleospora salmonis (Microsporidia). Infects the nuclei of immature blood cells, causing a leukemia-like condition with anemia, swollen spleen and kidney (A). B. Gram stain of kidney reveals Gram-positive (blue) spores (arrows).
(Download full resolution TIFF image, 1.3 megabytes)

  Loma salmonae. Causes cyst-like structures (called xenomas) in the gills and other organs. This microsporidium infects salmon in both fresh and sea water. A. Gill of salmon with xenomas (arrows). B. Histological slide showing xenomas (X) and associated inflammation (bottom of image).
(Download full resolution TIFF image, 1.3 megabytes)