2.0 Whirling Disease and the Madison River 



2.1 Mechanism and Biology of the Disease 



"Whirling disease" is a disease of Salmonid fish (trout, salmon, whitefish) caused by a myxozoan 

 parasite known as Myxobolus cerehralis. This tiny parasite has a fairly complicated life cycle 

 which involves two hosts; a small aquatic worm (Tubifex tuhifex) and a fish. The fish becomes 

 infected after the triactinimyxon form of the parasite (the TAM stage) emerges fi-om the worm 

 and enters the water column. The parasite finds a salmonid fish, attaches to the fish and 

 penetrates the skin. The parasite eventually finds its way to the cartilage of the fish where it 

 develops into a mature spore. Spores remain in the cartilage and bone until the fish dies, 

 releasing spores into the water, which ultimately are ingested by the tubificid worms and the life 

 cycle starts all over (MTWDTF 2000). 



Once ingested, the parasite can affect nerves and damage cartilage which results in the abnormal 

 whirling or tail-chasing behavior exhibited by some infected fish. The neural damage and 

 pressure on nerves from inflammation due to the parasitic infection cause these and other 

 symptoms, which may include a black tail in younger fish. In older fish symptoms sometime 

 include deformities to the head or body (MTWDTF 2000). Table 1 lists the fish species in 

 Montana that have been found infected with the whirling disease parasite. 



Table 1. Salmonid species occurring in Montana that have tested positive for whirling disease (MTWDTF 

 2000). 



Common Name 



Scientific Name 



Susceptibility 



Found in 

 Madison? 



Rainbow trout 



Oncorhynchus mykiss 



Moiuitain whitefish Prosopium williamsoni 



Yellowstone cutthroat Oncorhynchus clarki bouvieri 



trout 



Westlope cutthroat Oncorhynchus clarki lewisi 



trout 



Bull trout 

 Brown trout 



Salvelinus conluentus 

 Salmo trutta 



All strains of rainbow trout 



tested to date are susceptible 



Susceptible 



Susceptible 



Susceptible 



Partial resistance 

 Partial resistance 



X 

 X 



X 



Evaluation of 1 995 and 1996 Creel Data and its Implications related to Whirling Disease 

 In the Madison River, Montana 



Montana Fish, Wildlife and Parks 

 March 12, 2002 



