Common Name 



Scientiflc Name 



Susceptibility 



Found in 

 Madison? 



Chinook Salmon 



Coho Salmon 

 Grayling 



OncorhjTichus tshawytscha 



Oncorhynchus kisutch 

 Thymallus arcticus montanus 



Very susceptible 



Quite resistant 

 Very resistant 



Most species of trout and salmon can be infected with the parasite but not all will develop 

 whirling disease. Scientists have found that the age of the fish when first exposed to the parasite 

 is very important (Ryce, MacConnel and Zale 1999). Very young fish are highly susceptible but 

 after a fish is nine weeks old it becomes resistant to whirling disease (Ryce, MacConnel and Zale 

 1999, E. Ryce, pers. comm. 2002). Newly hatched rainbow trout fry (one week old) had 

 significantly lower survival rates at any exposure than older fish (Ryce, MacConnel and Zale 

 1999). Other members of the trout and salmon family, such as mountain whitefish may be at risk; 

 however, rainbow trout appear to be the most susceptible trout species. Brown trout become 

 infected with the parasite, but they appear to have immunity to the parasite and have not been as 

 heavily impacted as rainbow trout (Opitz and Zale 1998). 



2.2 History of Whirling Disease on the Madison River 



The parasite that causes whirling disease was first discovered in Montana in rainbow trout in the 

 Madison River in December 1994. It was discovered during an investigation into the cause of a 

 major decline in the rainbow trout population in the upper Madison River. Prior to December of 

 1994 this parasite had never been detected in any fish in Montana. Monitoring of hatchery stocks 

 and limited inspections and testing of wild populations for this parasite had taken place for many 

 years prior to its discovery in the Madison River. These monitoring efforts increased 

 dramatically after the 1994 discovery of the parasite and a state-wide survey was initiated. As of 

 early 1998 nearly 300 individual waters have been tested and the parasite has been detected in 

 more than 85 individual sites in Montana (MTWDTF 2000). 



Evaluation of 1995 and 1996 Creel Data and its Implications related to Whirling Disease 

 In the Madison River, Montana 



MonUna Fish, Wildlife and Paries 

 March 12,2002 



