ENVS 605

What is it?

Whirling Disease is a malady of trout and salmon caused by a microscopic parasite that produces a spore. The water-borne parasite (Myxobolus cerebralis) may not directly kill trout, but fish heavily infested can become deformed or exhibit the erratic tail-chasing behavior from which the disease gets its name. Eventually, heavily infected young fish may die. The parasitic disease probably originated in Europe, where native brown trout have developed a natural resistance to the parasite. But these fish can still carry and transmit the spore.  Whirling disease was first observed in the United States around 1958. The parasite was accidentally introduced in Colorado in the 1980s through imported trout from a private hatchery. Whirling disease is thought to be a major factor in the declines of wild rainbow trout populations in certain Colorado waters. It's suspected that the outbreak of the disease may be linked to other environmental factors that aren't yet apparent. The parasite has been confirmed in 13 of Colorado's 15 major river drainages, including the Colorado, South Platte, Gunnison, Arkansas and Rio Grande rivers.

 

 

Why is it a problem?

The disease is present in many Colorado rivers and in a number of state hatcheries. Once the disease parasite is established in the wild, it can persist indefinitely, depending on environmental conditions.  

 

 

Management Techniques:

Although there is no practical cure to treat wild trout that are infected with the disease, current evidence suggests that stocking of hatchery trout exposed but not necessarily infected with the parasite into waters where whirling disease is known to exist does not increase the level of infectivity.  These efforts to reduce the parasite in hatcheries are proving to have some success.

 

• Hatcheries - Hatcheries are performing routine fish health samples.  Eight of Colorado's state hatcheries have tested positive for whirling disease. In some cases, this has amounted to only two spores. (More than 4 million spores can fit on the head of a pin). Routine fish health sampling indicates diminishing infections at some sites, a result of measures to reduce or eliminate whirling disease in hatcheries. Many hatchery trout will carry few, if any, spores. But as a precaution, the Colorado Parks and Wildlife will consider these trout "positive" until repeated hatchery tests find no spores. Additional steps, including the installation of an ultraviolet system at the Roaring Judy Hatchery to kill spores that cause whirling disease, are underway.

• Stocking - A policy implemented in spring 1995 prevents the stocking of trout from hatcheries testing positive into waters where whirling disease has not been found. This includes wilderness areas and streams where native trout may be restored. Trout from positive hatcheries will be stocked into waters where the parasite has been found to minimize the risk of contaminating other watersheds. Only trout from negative testing hatcheries can be stocked into waters where the parasite has not been found.

 

 

What can we do?

We can take precautions such as: U.S. Fish and Wildlife Service

• Do not transport any fish from one body of water to another.

• Do not dispose of fish entrails or other by-products that may hold spores into any body of water or into sinks.

• Drain boats, equipment, coolers, live bait wells and any holder of water which can hold the parasite.

• Thoroughly wash mud from vehicles, boats, trailers, waders, boots, fishing equipment and anything that comes in contact with spores or worms found in the stream bed mud.

• Never transport aquatic plants, and make sure all equipment is cleared of weeds after every use.

• Spores are particularly persistent in felt soled wading shoes. If you have any doubt about contamination, you may treat these with a solution of 10% chlorine bleach and water for at least 15 minutes. Thoroughly rinse with water before using your waders to prevent residual chlorine from entering streams.

 

 

Entities working on this invasive in the Gunnison Basin:

Although there are currently no entities working on Whirling Disease in the Gunnison Basin, the websites listed above recognize that the microbe is impacting fish in the Gunnison region.  There is not a specific management plan to treat this invasive microbe in the Gunnison Basin, but if you have specific questions please contact the US Fish and Wildlife Service extension in Gunnison at 970-641-7060.

 

 

General Information on Whirling Disease:

Whirling Disease General Information

• Website that provides an overall and comprehensive summary of Whirling Disease

 

National Invasive Species Information Center, Microbes

• Website that provides information about Whirling Disease

 

US Fish & Wildlife Service Whirling Disease

• A news release with information and management techniques for Whirling Disease

 

CSU Extension

• Website that provides current research on Whirling Disease