Whirling Disease Documented

First Time In Wild Fish Of Arizona’s Public Waters

PHOENIX – Laboratory results for trout routinely sampled at Lees Ferry by Arizona Game and Fish Department biologists this spring came back positive for whirling disease on June 13, marking the first time this disease has been documented in wild fish in Arizona public waters.

Whirling disease is a parasitic infection of trout. It gets its name because the parasite infiltrates the head and spinal cartilage of small, fingerling trout and can cause the fish to swim erratically (whirl). More information on the disease can be obtained from the Whirling Disease Foundation at www. whirling-disease.org or at www.whirlingdisease.montana.edu .

“We have seen no clinical symptoms of whirling disease in trout at Lees Ferry. This is likely an early detection. Based on our sampling so far, it appears there is a low level of infection in the trout population there. We are stepping up our monitoring efforts to stay on top of the situation,” says Fisheries Chief Ty Gray.

The department will conduct additional sampling of trout in July and October to further assess the extent of the disease in the trout population. 

Game and Fish biologists stress that whirling disease does not affect humans or other fish species; it is only known to affect trout. Although there is no known method for eradicating this disease in the wild, efforts in other parts of the country indicate that management and control are possible.

The department has been sampling for whirling disease at Lees Ferry repeatedly since 1999. Until now, all samples have been negative. The department has not stocked or authorized any trout stocking at Lees Ferry since 1998. All department hatcheries are annually inspected for whirling disease and remain free of the disease.

Possible pathways for whirling disease introduction include the movement of infected fish as well as being transported by wildlife (birds), humans, or water. The nearest whirling disease positive site within the Colorado River drainage is on the San Juan River in New Mexico. However, determining the actual pathway of whirling disease into Lees Ferry will be difficult if not impossible.

“Obviously we're concerned about the potential impact this new development might have, and we'll immediately increase management activities, but we have no reason to believe it will affect the quality of fishing at this world-class blue-ribbon trout fishery any time soon, if at all,” says Gray.

Jeff English, a guide with Lees Ferry Anglers, says that right now the Ferry is experiencing its best fishing in five years and trout are in great condition. “There are 16- to 18-inch fish up near the dam that are fat-bellied, hard-fighting beasts that are routinely breaking lines.”

Game and Fish officials are asking anglers and other recreationists who visit the Ferry to take some simple and easy precautions to help prevent the spread of this disease to other trout waters in the state. 

•  Never transport live fish from one water body to another (this is illegal in Arizona ).

•  Dispose of fish entrails and skeletal parts properly. Never discard fish parts in or near streams or rivers. Do not discard fish parts in a kitchen disposal. Whirling disease spores can survive most wastewater treatment systems. Instead, discard in dry waste that would go to a landfill.

•  Rinse all mud and debris from equipment and wading gear, and drain water from boats before leaving an infected drainage. This is good practice for preventing transfer of other aquatic hitchhikers as well.

Anglers interested in ways to best treat their equipment should visit http://www.whirling-disease.org/files/wd_prevention.pdf for more tips.

Game and Fish officials said that although this is the first known case of whirling disease in Arizona public waters, trout from whirling disease positive facilities have been stocked into private waters as early as 2000.

The trout for the private ponds originated from hatcheries outside Arizona that tested positive for the disease after the fish had been delivered to Arizona . In each case, immediate remedial treatment steps were taken to eliminate potential establishment of the disease. Subsequent testing at these waters demonstrated that the efforts were successful.

“No wild trout in Arizona have ever been documented to have whirling disease until now, although we now join all the other western states that are contending with this disease,” Gray says.

Frequently Asked Questions

1. What is whirling disease and do all fish get it? Whirling disease is a parasitic infection that attacks juvenile trout and salmon, but does not infect warm-water species. All species of trout and salmon may be susceptible to whirling disease.

Rainbow trout and cutthroat trout appear to be more susceptible than other trout species. The parasite can infect brown trout, but they appear to have some immunity to the infection and have not been as greatly impacted as rainbow trout. Studies in Montana and at the University of California-Davis have demonstrated that grayling and bull trout are very resistant to infection.

2. Does whirling disease pose a threat to struggling populations of native fish in the Grand Canyon ? No. Whirling disease only poses a threat to trout. However, if the disease is spread to other areas of Arizona , it could possibly jeopardize populations of native Apache and Gila trout. Anglers can take simple steps to help ensure that doesn't happen.

3. Where is whirling disease found? Whirling disease is found in 25 states including Alaska , Arizona , California , Colorado , Connecticut , Idaho , Maryland , Massachusetts , Michigan , Montana , Nebraska , Nevada , New Hampshire , New Jersey , New Mexico , New York , Ohio , Oregon , Pennsylvania , Utah , Virginia , Washington , West Virginia , and Wyoming , and in several European countries, in South Africa , and in New Zealand .

4. Can humans get whirling disease? No, the parasite can't infect humans.

5. Does whirling disease always destroy trout populations?  No.  Although the parasite is established in hundreds of waters, its presence does not always mean whirling disease will cause dramatic population losses.

6. How is whirling disease transmitted? Whirling disease is transmitted by infected fish and fish parts. It may also be transmitted by birds, and it is possible fishermen could carry the disease on fishing equipment. However, live infected fish are the main vector for the spread of the disease.

7. How can I prevent the spread of the disease? First and foremost, do not transport live fish or carry fish or fish parts from one drainage to another. If fishing known whirling disease-infected waters, care should be taken to rinse all mud and debris from equipment and wading gear, and drain water from boats before leaving the infected drainage.

8. What are the Arizona Game and Fish Department and others doing to prevent the spread of this disease? The first and most critical step is informing anglers and enlisting their support to not unintentionally spread this disease from Lees Ferry to other waters.

The department has been routinely sampling for this disease for eight years and will now ramp up its sampling efforts accordingly. Signage will also be placed at the Ferry informing anglers of the suspected infestation.

Although eradication does not appear possible, the department is exploring every management tool available and will deploy those best suited for conditions at the Ferry.