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IHN Fish Virus found at Oregon's Butte Falls Hatchery

May 23, 2006

Roseburg – Oregon Department of Fish and Wildlife officials today announced that fish sampled from several stocks at Butte Falls Hatchery tested positive for the infectious hematopoietic necrosis virus (IHNV), a virus that is not harmful to people but can kill fish.

IHNV is a naturally occurring virus that initially attacks the blood-forming tissues of the kidney in salmon and trout. External symptoms include lethargy, darkening of the skin and hemorrhaging at the base of the fins. Past experience shows that hatchery fish losses can increase dramatically from this disease, which has no known treatment. However, some fish carry the virus for their entire life cycle without any health problems and it usually causes mortality outbreaks only when fish are stressed.

ODFW’s hatchery and disease policies maintain a strong focus on preventing the spread of pathogens to areas where they do not naturally occur by regulating releases of fish. ODFW fish biologists are working to coordinate hatchery releases so the virus does not spread to IHNV-free waters, while also maintaining legal-sized trout releases for the remainder of the season. So far, the season’s trout releases have been successful, with early releases into urban ponds, additional releases into Agate Lake, and extra fish for some of the area’s other lakes.

Fisheries biologists believe the hatchery was likely exposed to IHNV from adult wild steelhead above the water intake. Passage above Butte Falls is highly dependent on water flows in a particular year and higher than normal water flows in Big Butte Creek this year allowed many more adults to spawn upstream. Steelhead and coho salmon have been found upstream of the falls in previous years.

Samples that tested positive for IHNV came from the Butte Falls Hatchery’s legal-sized and fingerling rainbow trout, fall Chinook stocks intended for the Coquille River, and winter steelhead being reared for the South Umpqua River. The virus is not currently present in either river system so biologists are considering options for stocking these rivers with IHNV-free fish.

The rainbow trout fingerlings that tested positive were being reared for release in Howard Prairie Reservoir. Last week, Willamette Hatchery stocked legal-size trout in Howard Prairie Reservoir and Hyatt Lake.

The Butte Falls legal-sized trout that tested positive were scheduled for release in the Rogue River above Lost Creek, Medco Pond and Willow Lake. Willamette Hatchery will step in and provide some legal-sized trout for the Rogue River above Lost Creek. “We’re working to minimize the impacts of the detection of IHNV to anglers,” noted Rogue District Fish Biologist Dan Van Dyke. “Stocking the Rogue River above Lost Creek is a high priority for the district along with area lakes that still need to be stocked.”

Recent tests also confirmed IHNV’s presence at Cole Rivers Hatchery in juvenile rainbow trout and in juvenile winter steelhead that were destined for release into the Applegate River next year. These fish were exposed to IHNV earlier this month when adult winter steelhead escaped broodstock holding ponds and entered the water supply conduit. The hatchery has installed redundant screening to prevent fish from escaping holding ponds in the future.


 

 
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