Protect Threatened Steelhead

A new and highly effective approach to control a viral pathogen that affects threatened steelhead trout in an Idaho hatchery is documented in a new paper. Researchers confirmed that the water supply from a reservoir could be used in such a way that juvenile steelhead were not exposed to river water at a time when infected adult steelhead fish contaminated the river water. This action drastically reduced mortality in juvenile fish.

The virus infects both adult and juvenile fish but causes disease and sometimes death in juvenile fish. There is a well known form of this virus that is particularly deadly for steelhead trout. There are no treatments for infected fish and it can be a difficult pathogen to manage and a devastating one if juvenile fish start to suffer epidemic disease.

After experiencing severe losses to to the virus in the steelhead trout program at Dworshak National Fish Hatchery in Idaho for years, managers and fish health specialists from the U.S. Fish and Wildlife Service worked with researchers from the U.S. Geological Survey to identify the source of the problem and developed a strategy to control it.

"This virus has been devastating to our hatchery steelhead," said Steve Rodgers, Manager for the Dworshak Fisheries Complex. "These losses have meant far less adult steelhead for harvest by sport and tribal anglers, which is the very reason the hatchery is here. This study will help us reach our goals."

Analysis of virus samples taken from juvenile and adult fish in and around the hatchery provided evidence that the source of infection was from IHNV-infected adult trout in the river where the hatchery gets water for rearing juvenile fish. Based on this evidence, hatchery personnel worked with the Army Corps of Engineers, who own the facility, to modify the water delivery system. This modification allowed for extended rearing of juvenile steelhead trout on Dworshak Dam reservoir water, which does not contain adult fish infected with the virus. This strategy was implemented in 2010 and has resulted in an immediate and dramatic reduction in virus-caused death among Dworshak juvenile steelhead trout ever since.