California Department of Fish and Wildlife says an outbreak of whirling disease in trout populations at the Mt. Shasta Hatchery was caused by fish transferred from its Darrah Springs facility east of Redding. CDFW said whirling disease poses no risk to humans or other animals, and plans are continuing for Saturday's fishing derby in Mount Shasta.

Confirmation of the presence of whirling disease in trout populations at two California Department of Fish and Wildlife hatcheries was described by statewide program manager Bill Cox as “a severe hit to our operations.”

Cox and two other CDFW representatives spoke about the situation and what is being done to correct it at the Mt. Shasta and Darrah Springs hatcheries during a media conference call Thursday afternoon.

The exact number of infected fish had not yet been determined, but CDFW said approximately three million rainbow and brown trout at those two hatcheries are under quarantine while further testing is being done.

That’s nearly a third of the approximately 10 million trout being raised at state-run hatcheries.

Cox said quarantined fish from the two facilities can not be used to stock local recreation areas, but CDFW will “deploy fish” from other facilities for that purpose.

Whirling disease can be fatal to infected trout and salmon, but poses “no risk to humans or other animals or organisms,” said Mark Clifford, CDFW’s Fisheries Pathologist at the Mt. Shasta Hatchery.

CDFW Fisheries Branch Chief Stafford Lehr said infected fish have to be destroyed, and that process has begun. The infected fish can be euthanized in a manner that allows for use as food. CDFW said it is reaching out to local food banks to try to make use of the fish.

The kids fishing derby scheduled for Saturday at the Mt. Shasta Hatchery is going forward as planned, said Clifford.

He described the known outbreak at the Mt. Shasta Hatchery as “very discrete and isolated. Some smaller fish have been euthanized and removed, with careful disposal of carcasses.”

CDFW said it is not yet known if biological and environmental conditions have allowed the parasite involved in whirling disease to complete its “complex lifecycle” at the Mt. Shasta Hatchery. “We think we found this in time and are working as quickly as possible to halt the cycle,” Clifford said.

Drought-related

Stafford said the last outbreak of whirling disease infection in a California hatchery was in 1986.

CDFW believes this outbreak is related to drought.

Lehr said the outbreak was first confirmed by DNA testing about two weeks ago at Darrah Springs, east of Redding in the Battle Creek watershed.

Cox said the Battle Creek watershed is “a known positive whirling disease basin.” He described how terrestrial animals that are migrating in that area because of the drought may have transferred the parasite associated with whirling disease to the water supplying a portion of the Darrah Springs Hatchery.

Some species of fish-eating birds, including herons and egrets, can transmit the parasite, and river otters and bears can carry it on their fur, according to CDFW.

Making sure the disease is removed from the hatcheries after all the infected fish are destroyed is a process that could take two years, said Lehr. It involves draining ponds, coating them with an epoxy, and installing an ultraviolet disinfection unit on the water supply that feeds the hatcheries.

As far as is known now, Clifford said the water supply and water downstream of the Mt. Shasta Hatchery is not positive for the parasite associated with the disease.

“We won’t be remiss in testing fish at and below the facility and everywhere we can,” he said.

From one hatchery to another

The disease at Darrah Springs was discovered during what CDFW described as “routine hatchery and fish health checks.”

Because Mount Shasta had received fish transferred from Darrah Springs about four months earlier, Lehr said testing was done at Mt. Shasta and the disease was confirmed to be present there.

Asked about implementing testing closer to the dates when fish are transfered from one hatchery to another, Stafford said he expects that to be considered as they do more analysis of this outbreak.

“This was unexpected after 30 years,” said Cox.

Stafford said during the conference call that about 400 pounds of “very small fish” had been destroyed in the previous 24 hours, and CDFW is trying to make arrangements with food banks “to get some use out of larger broodstock” that need to be euthanized. He estimated about 6,000 to 7,000 infected fish in that category weighing about 14,000 pounds.

Lehr said whirling disease was imported from Europe and has been known in California since 1965.

It is caused by Myxobolus cerebralis, a protozoan parasite that destroys cartilage in the vertebral column of trout and salmon, according to the CDFW press release.

Clifford said fish used for Saturday’s kids fishing derby at Mt. Shasta will not be from the infected population, but CDFW will take the added precaution of cleaning fish for kids and will dispose of the carcasses “in a way to not encourage the spread of the parasite.”

Cox said CDFW will be looking at its statewide operations to determine future stocking of northern California recreational areas. “We have the ability to make adjustments,” he said, “although the statewide system recently underwent a reduction in production because of budgetary considerations.”

For more information on whirling disease, CDFW suggests the website: http://whirlingdisease.montana.edu.