A parasite that deforms the spines and skulls of trout - making them swim in circles often until they die - has infected 80,000 fish in two hatcheries in Western Maryland, state officials said yesterday.
The "whirling disease," which has devastated trout populations in Western states, has also been found downstream from the two Maryland hatcheries, in the North Branch of the Potomac River, said Bob Lunsford, director of freshwater fisheries for Maryland Department of Natural Resources.
"We are testing all of the places that we know have wild trout populations so we can get a handle on how widespread this parasite is," Lunsford said.
State officials killed the 80,000 infected fish at the Bear Creek Rearing Station near Accident and in another privately owned hatchery used by the state in southern Garrett County.
The result will be that state officials will be stocking streams and lakes across Maryland this spring with about 20 percent fewer rainbow and brown trout, meaning fishermen will have fewer to catch, Lunsford said. Last year, the state stocked 197 streams and ponds with 418,250 trout.
The parasite, Myxobolus cerebralis, is not a risk to humans or other fish, Lunsford said. He said it might have been spread to the hatcheries by mud on the feet of birds or bears.
Nathaniel Gillespie, a fisheries scientist with Trout Unlimited, a nonprofit group, said the invasive species was spread from Europe to the United States in the 1950s. It hit Colorado and Montana hard, and has spread to 22 states, including Pennsylvania, Virginia and New York.
"It has had some devastating effects on wild trout populations across the country," said Gillespie. "It's pretty grotesque. You see them swimming in a circle, because their spines are crooked."
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 at the "growing out" facility (where trout are fed until large enough for release) had apparently picked up the parasite from wild trout in the river, Lunsford said.
State biologists isolated the infected fish in a 20-mile stretch of the river, between dams at Jennings-Randolph Lake and Westernport, Lunsford said.
But last month, test results came back showing thousands of infected fish several miles away at the hatcheries. "It was terribly depressing," Lunsford said.
The Bear Creek center receives about 150,000 young rainbow trout from other hatcheries and raises them until they are large enough for release. Employees this winter noticed that many young fish - about three months old, 1 1/2 inches long - were acting oddly. "They have peculiar whirling swimming patterns, and it looked like they were spinning," Lunsford said.
The parasites live in the skulls and spines of fingerling trout, warping their bodies, deforming their heads and blackening their tails. The fish that survive into adulthood carry the parasites and reproduce, then shed millions of spores into the water when they die, according to the Whirling Disease Foundation. The spores are then eaten by tiny worms, which carry the parasites until they grow and infect fish.