By Amy Nelson
anelson@newsroom.byu.edu
Fish populations from local hatcheries will be about 21 percent smaller this year because of whirling disease, a parasitic disease which causes fish to whirl around in circles in the water.
According to Utah's Division of Wildlife Resources (DWR), the disease was found in rainbow trout at the Midway State Fish Hatchery and will cause a loss of more than 300,000 fish.
DWR Media Specialist Mark Hadley said the Midway Hatchery is the first in Utah to test positive for the parasites that cause the disease through innovative DNA testing methods.
The affected fish were located in dirt raceways at the lowest portion of the hatchery closest to Deer Creek Reservoir, where the presence of the parasite was confirmed, Hadley said.
He said fish in the upper concrete raceways, where it is more difficult for the parasite to survive without a host, tested negative for the parasite.
Hadley said biologists suspect the parasite may have been introduced to the hatchery system by fish-eating birds or other predators common to the area.
DWR Information and Education Manager Scott Root said whirling disease is caused by a microscopic parasite known as Myxobolus cerebralis, which attacks the cartilage tissue of a fish's head and spine.
Once infected, the fish may develop whirling behavior, a black tail, head deformities and twisted spines, Root said.
'Fish start whirling around in circles,' Root said. 'It's not harmful to humans, but we don't want diseased fish.'
Root said that Utah used to have very clean fish-very prized trout eggs that could be traded with other states-but now that the Midway Hatchery has had whirling disease found in it, the clean status may be in jeopardy.
Although the primary spread of the parasite happens when an infected fish dies and releases thousands of spores into the water, Root said that it can also be transported through mud in tires or dripping off a boat that has been in infected waters. He said that the concrete hatcheries can be drained and cleaned to get rid of the parasite, but when there is dirt and mud under the water, it can't really be treated because the parasites will survive there.
'We've spent thousands upon thousands of dollars trying to safeguard against this, but it's difficult,' Root said.
To help salvage the fish populations, affected fish are being removed from the hatcheries and fish production will be limited to the concrete raceways where fish are less susceptible, Hadley said. To make best use of the catchable fish that are available, DWR will put most of them into lakes and reservoirs where they have a better chance of survival and return to anglers, Hadley said.
The Whirling Disease Foundation's Web site says that when infected with the disease, fish may also be more susceptible to predators, less able to feed, and less able to survive natural disturbances. It says fish that contract parasite early in life are susceptible to death, but if they have developed sufficiently they are more likely to live to maturity.
At this time there is no known treatment or cure for whirling disease, although it has been demonstrated that it can be controlled in hatchery environments, according to the DWR. It was first discovered in Utah in 1991, but it has been in the United States since the late 1950's. To date, 22 states have reported the disease.