RICHMOND – Through recent testing, the Virginia Department of Wildlife Resources (DWR) has detected whirling disease in catchable sized trout at the state’s Marion Fish Hatchery in Southwest Virginia. DWR’s stringent fish-health protocols involve regular testing at state hatcheries to look for pathogens that are potentially harmful to hatchery raised and wild fish. DWR does not stock known whirling disease positive fish.
Regrettably, DWR has had to euthanize 40,000 catchable trout to control whirling disease. This represents about a 20% reduction in normal stocking levels for Southwest Virginia and a 5% reduction statewide. Consequently, trout anglers are likely to see a reduction in trout stocking, particularly in Dickenson, Buchanan, Wise, Lee, Scott, Russell, Washington, Smyth, Tazewell, and Grayson Counties. DWR is working to reallocate fish as feasible to make up for shortfalls and is implementing measures to reduce the future impact of this parasite on trout production.
Whirling disease is caused by a microscopic parasite, Myxobolus cerebralis. This parasite penetrates the cartilage tissue of a trout’s head and spine, multiplying rapidly and causing skeletal deformities. Trout with whirling disease can show spinal deformities or a blackened tail, which can impact swimming ability and feeding habits. Some infected fish swim in a circular motion, giving the disease its “whirling” name. Fish showing these distinct symptoms have not been seen in the wild or at state hatcheries in Virginia.
This disease is fairly widespread and has been documented in more than 20 states including Virginia. Native to Europe, this parasite and disease were first detected in the United States in 1958. The parasite has a two-host lifecycle including small worms (tubifex worms) and trout. Both hosts are required for the parasite to complete its lifecycle. The host fish must be a salmonid, with rainbow trout being the most susceptible to the parasite. The parasite does not infect humans, even if you eat infected fish.
Virginia Department of Wildlife Resources