Whirling Disease Detection Triggers Quarantine at Two California Trout Hatcheries

The detection of a disease-causing parasite has led the California Department of Fish and Wildlife (CDFW) to quarantine infected trout at two northern California hatcheries.

During routine hatchery and fish health checks, CDFW fisheries pathologists found that captive-raised fish at the Darrah Springs Trout Hatchery (located in the Battle Creek watershed east of Redding) tested positive for whirling disease. Prior to the discovery, trout were transferred from an infected raceway at Darrah Springs to Mt. Shasta Hatchery. While fish transferred to  Mt. Shasta Hatchery from Darrah Springs Hatchery tested positive for the parasite, it is yet unknown if biological and environmental conditions allowed it to complete its lifecycle at that location. Approximately three million rainbow and brown trout at both hatcheries are now under quarantine and will undergo testing.

Whirling disease is caused by Myxobolus cerebralis, a protozoan parasite that destroys cartilage in the vertebral column of trout and salmon. It can be fatal to infected trout and salmon but does not affect humans or other wildlife or fish. Trout and salmon that test positive for the disease are still safe for human consumption. Although the infected hatchery fish cannot be released into California’s waterways, they can and will be euthanized in a manner that allows for usage as food fish. CDFW is currently working with local food banks to arrange donation, and a previously scheduled children’s fishing event at the Mt. Shasta Hatchery this weekend will be held as planned.

The whirling disease parasite is naturally present in some streams and rivers in California. Hatchery outbreaks are unusual but not unheard of (there have been none in northern California for two decades). The disposal of infected hatchery-raised trout is a necessary precaution to prevent the spread of disease to non-infected state waters where the fish would normally be planted.

“This is a bitter pill to swallow,” said Stafford Lehr, CDFW Fisheries Branch Chief. “We have raised and nurtured these trout to provide fishing opportunity. It’s heartbreaking. We are committed to take whatever steps necessary to eradicate this disease and bring these hatcheries back online.”

The parasite is believed to have entered Darrah Springs Hatchery via the water source supplying a portion of that hatchery. Some species of fish-eating birds can transmit the parasite and river otters can carry it on their fur from one water to another. The possibility that the parasite was transferred to the hatchery from local nearby waters known to have whirling disease is likely, due to current drought conditions that cause wildlife to move to available water sources.

Until testing is complete the exact number of fish exposed to and infected with the disease is unknown. Once the infected fish are euthanized, the latest scientific techniques will be used to cleanse the impacted areas of the hatcheries, confirm the impacted water sources are whirling disease-free and bring the facilities back to production status as soon as possible.

CDFW pathologists routinely inspect each of the 13 state-run trout hatcheries which raise approximately 10 million trout for California anglers statewide, and nine salmon hatcheries that raise over 31 million young salmon and steelhead.

For more information on whirling disease, please visit http://whirlingdisease.montana.edu.

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Media Contacts:
Harry Morse, CDFW Communications, (208) 220-1169

Dr. William Cox, CDFW Hatchery Program Manager, (916) 358-2827