The New Mexico Department of Game and Fish is investigating the source of whirling disease that led to thousands of fish being culled at the Rock Lake State Fish Hatchery in Santa Rosa.
Whirling disease is caused by a parasite and is named for the “whirling” behavior that some infected fish perform. The parasite attacks the cartilage tissue in the fish’s head and spine, leading to deformities. Infected fish can also develop a black tail.
The parasite primarily affects salmonid species including trout and salmon. It does not pose a threat to human health, though it can be fatal to the infected fish and there is no known effective treatment.
Whirling disease was first detected in New Mexico in 1998, according to the U.S. Forest Service, and is currently present in waters in the Santa Fe National Forest including Rio Cebolla, Jack’s Creek and the Pecos River.
The parasite originated in Europe and likely came to the United States with the brown trout. Because of that, the brown trout is less susceptible to whirling disease, but hatchery rainbow trout and native trout species like the Rio Grande cutthroat are considered highly susceptible to it.
Last week, the New Mexico Department of Game and Fish announced that some of the animals at the Rock Lake Hatchery have been infected with whirling disease.
This was the first time since 2007 that the parasite has been found in hatchery waters in the state, though it has been present in other New Mexico waters.
The discovery led to 70,000 fish being euthanized at the facility.
The fish at the Rock Lake hatchery were in large, concrete troughs known as raceways, according to an email from Ryan Darr with the New Mexico Department of Game and Fish in answer to questions from NM Political Report.
He said the water flows through the raceways, but “is not recirculated or distributed to any other part of the hatchery.”
“In a series of raceways it is possible for the upstream units to contaminate those that are downstream,” Darr said. “All of the potentially exposed fish at Rock Lake are being euthanized.”
He said the affected fish were about six to 10 inches long and around 10 to 15 months old.
“In the rare instance that a whirling disease infection is detected, the current protocol is to euthanize the infected fish, dispose of them in a landfill where they will be immediately buried, disinfect the area of the hatchery where they were being raised, and increase monitoring in that area as new fish are brought in,” Darr said in the email.
He said that it is possible that some of the infected fish may have been stocked in rivers or other waters in New Mexico.
Darr said many of the waters in the state already have whirling disease in them and those areas would not be affected by infected fish from the hatchery being released into them.
Additionally, Darr said the infection rate at the hatchery was extremely low and the Rock Lake Hatchery primarily stocks waters that are considered winter trout waters. Winter trout waters are locations where the trout cannot survive the warm summer water temperatures.
“In those locations, the risk posed by whirling disease is nearly nonexistent because the waters do not support wild trout populations and the disease cannot complete its life cycle in the absence of a reproducing trout population,” Darr said.
The source of the hatchery infection remains unknown. It was detected during an annual disease survey and Darr said no clinical signs of a whirling disease outbreak were observed.
Whirling disease can be carried from one waterway to another on birds, animals, boats, wading boots or other equipment that is moved from one waterway to another.
The public can help prevent the spread of whirling disease by cleaning gear, including boats and flyrods, before entering streams, rivers, lakes or other bodies of water.
More information about whirling disease can be found here.