A parasite, which deforms the spines and skulls of trout causing them to swim in circles till they die, has affected two hatcheries in West Maryland, U.S. The disease is referred to as 'whirling disease'.
It has resulted in the plan to cull around 80,000 of the fresh water fish.
The parasite, Myxobolus cerebralis, has long been known to exist in the Potomac River's North Branch, which are several miles from both hatcheries. It is harmless to humans, but can be deadly to trout and especially Rainbow trout.
According to Robert Lunsford, director of Freshwater Fisheries, it might have been spread to the hatcheries from mud on the feet of birds or bears, which are plenty in this region.
The microscopic protozoan was first detected in Maryland 12 years ago, in a state trout-raising facility in the North Branch of the Potomac. The fish being held in nets until large enough for release, had apparently picked up the parasite from wild trout in the river.
The department has asked that those catching fish follow certain precautions to reduce the possibility of spreading spores of the harmful organism.
Fish should not be moved between streams and fish carcasses should not be discarded in a stream or on its banks. Mud should be cleaned from boots and fishing equipment before shifting streams.