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Parasites and Pathogens

ANS—Parasites & Pathogens


Montana ANS Priority Class 1


  • First wild fish discovery in 2000
  • A protozoan (Microsporidean) that infects and degrades muscle of yellow perch and other species
  • Symptoms: white and opaque flesh
  • Distribution: Wisconsin, Minnesota & Ontario
  • Infected filet should be disposed of in the garbage, burned or buried.
  • Prevent by drying all equipment and cleaning live wells and bilges away from lake
  • Full lifecycle unknown

IHN Virus

Montana ANS Priority Class 1


  • Infectious Hematopoietic Necrosis (IHN) Virus
  • Synonyms: Sockeye salmon virus, Oregon sockeye virus, Sacramento River chinook disease, Sacramento River chinook virus
  • Symptoms: lethargy, swim high in the water column, anorexia, popeye, pale gills, darkening of body, abdominal distention

Whirling Disease

Montana ANS Priority Class 2


Whirling Disease. Whirling disease in young fish.
  • First discovered in Montana in 1994
  • Native to Europe
  • Caused by the myxozoan parasite Myxobolus cerebralis
  • Parasite digests the cartilage of young trout, especially in rainbow trout
  • Deformities reduce ability to survive by impairing swimming and feeding ability
  • The parasite has a complex life cycle involving a salmonid host and the worm Tubifex tubifex


The Whirling Disease Foundation

Asian Tapeworm

Montana ANS Priority Class 3


  • Bothriocephalus acheilognathi
  • A cestode that infects anterior intestine of fish.
  • Spread by ingestion of infected copepods
  • Fish host species: Primarily
  • Cyprinidae except for gold fish.
  • Optimal temperature: 25°C
  • Detected in southern half of US, NH, NY, Hawaii
  • Identification: Bothria, pyramid- shaped scolex and segmented body