Virus detected in Kootenai River salmon

In November, state fisheries biologists detected a virus in wild spawning kokanee salmon below Kootenai Falls on the Kootenai River. It’s the first time the common infectious virus, hematopoietic necrosis, has been detected in state waters, according to a press release by Montana Fish, Wildlife & Parks.

The virus doesn’t pose a threat to humans who come into contact or consume infected kokanee. The disease occurs naturally in Pacific Coast wild salmon, steelhead, and herring and can be passed to other fish. It has been found in portions of the Kootenai River in Canada and Idaho, but it’s unknown how long the virus has been in Montana waters.

Hematopoietic necrosis has been tested for in Montana for about 20 years, but testing in the Kootenai River began in 2013 when the ailment was found in fish along stretches of the river in British Columbia.

It’s not known how the disease impacts wild populations, but in hatcheries the virus can be lethal. Young fish are most susceptible to disease, particularly during the first two months of life. If an outbreak occurs the cumulative mortality rates on these farms can reach 90-95 percent. Resistance to infection increases in older fish, where the disease is uncommon.

Because the disease is new to the area Doug Hensler of Fish, Wildlife, & Parks has mild concern for the situation, but said they will continue to do more research on the effects of the disease on kokanee.

There is one thing working in favor of biologists keeping track of the disease in the area. “You pretty much need a spawning fish and we have the ability to catch spawning kokanee way better than a rainbow or bull trout.” Spawning male and female kokanee can be captured at Middle Thompson Lake in October and screened for the disease.  

Outbreaks of the disease have happened in hatcheries from California to Alaska leading Fish, Wildlife & Parks to redouble efforts to keep the virus from spreading to kokanee brood stocks in Lake Mary Ronan, and nearby fish hatcheries at Murray Springs near Eureka and the Flathead Lake Salmon Hatchery near Somers.

“Of all the states in the nation, at least in my opinion, Montana is the best when it comes to keeping disease out of our waters. We take pride in that. So it’s a big deal to us to understand where it might be and where it could get,” Hensler said.

A vaccine for the virus does exist, but it is expensive and has not been approved for use in the United States. It has also show to have limited effectiveness outside of hatchery settings.

Hematopoietic necrosis attacks the blood-forming tissue of the kidneys and can be transmitted by infected fish that may not show symptoms of the disease. The virus is spread from the feces, urine, sexual fluids and external mucus and is transmitted primarily by direct contact, but also through the water. Hematopoietic necrosis can survive in water for at least one month.

 In an interview with fish pathologist for British Columbia’s Ministry of Agriculture Dr. Gary Marty heard on a Canadian Broadcast Corporation radio show said studies showed rainbow trout eating infected salmon eggs did not develop the disease.  “You always have to study the specific area and the specific outbreak to be sure, and I think that is planned, but so far the risk to other species is low and probably actually even to the kokanee in the lake, probably low,” Marty said about the fish in Kootenay Lake.

In the press release from Fish, Wildlife, & Parks it said the best defense for protecting Montana’s waterways is for people to get into the habit of inspecting, cleaning and drying their boats, trailers, and fishing gear after each use.

“Think about that stuff. You don’t want to impact your next favorite place to go fishing,” Hensler said.