2nd Incident of Possible Exposure to Whirling Disease In Arizona

                Trout that might have been exposed to whirling disease – a parasitic organism that has impacted many trout fisheries in the nation – were stocked in March from a private hatchery in northwestern Colorado to a small private pond in Arizona, advised Arizona wildlife officials.

            Arizona Game and Fish Department officials said that the importation was a legally permitted action, with a valid “Aquatic Wildlife Stocking Permit” issued, accompanied by a valid fish health certificate from the hatchery. This is the second unintentional importation event in two years.

            Subsequent inspection (April of 2001) and confirmatory testing (May of 2001) by the Colorado Division of Wildlife determined that fish from the private hatchery in northwestern Colorado were positive for whirling disease.

            The privately owned hatchery made its only shipment to Arizona early this year to a very small private pond in Navajo County. The pond is a constructed upland pond filled with well water and has no natural inlet or outlet. Because of its isolation it does not affect any other trout water or natural drainage. There is no public access to this private property.

            Whirling disease can result in high mortality rates for young fish and has impacted fisheries in many other western states. “Our goal is to keep whirling disease out of Arizona and Arizona’s fisheries,” said Fisheries Branch Chief Larry Riley.

            Arizona Game and Fish officials pointed out that the presence of the disease in Arizona fish has not been confirmed. “We have not confirmed that infected fish were stocked, however, we are treating them as whirling disease exposed,” Riley said.

      Arizona Game and Fish and the Arizona Department of Agriculture are working cooperatively with the private landowner to test the fish for the presence of whirling disease and develop and implement a plan of action that is responsible to the state’s fisheries resources and fair to all parties.

      Whirling disease is not a public health issue. Arizona Department of Agriculture state veterinarian, Dr. Rick Willer, said, “Whirling disease is not transmittable to people. And in fact, trout infected with the disease are safe to eat.”

      Whirling disease caused by Myxobolus cerebralis, is a microscopic (metazoan) parasite that penetrates the cartilage of trout and destroys it. One clinical sign of the disease is the erratic swimming behavior (whirling) of very young fish which gives the disease its name. Those fish also have difficulty feeding and avoiding predators. The disease can result in high mortality rates for young fish.

      Records from the Arizona Department of Agriculture and the Arizona Game and Fish Department indicate that fish were stocked at a single site here.

      Arizona Game and Fish personnel have personally contacted the private recipient of fish from the private Colorado hatchery and are working closely with them on remedies to eliminate risks to Arizona fishery resources from whirling disease.

      It is important to note that this discovery does not involve state or federal trout hatcheries in Arizona nor does it appear to affect sensitive trout waters in Arizona - sites of naturally reproducing trout or sensitive native trout. Developing a plan of action for this site will help to minimize any potential for effects to sensitive streams in Arizona.

      Among fish found in Arizona, rainbow, cutthroat and brook trout are the most susceptible species. Brown trout and grayling are considered less susceptible, and the disease has not been documented in Arizona’s two native trout, Apache and Gila, although biologists suspect they may be susceptible. Other species of game fish, such as bass or crappie, do not contract whirling disease.

      In severe infections, the disease can cause high rates of mortality in young-of-the-year fish. Those that survive until the cartilage hardens to bone can live a normal life span, but may be marred by skeletal deformities. Survivors carry “spores” of the parasite that continue the parasite’s life cycle.

      Whirling disease has a complex life cycle, which involves two hosts: trout and tiny aquatic worms called tubifex. Worms that become infected release a fragile state of the parasite that must infect a trout within a few days or perish.

            Infected trout carry spores that are very persistent, but the trout can survive for years. The spores are released when an infected fish dies and decomposes. The whirling disease parasite can survive passage through the digestive tract of a predator and there is a remote possibility that the disease also can be transferred from place to place on muddy boots or equipment.

Want to learn more: 

Read about the Life Cycle at this New Mexico source