The Oregon Department of Fish and Wildlife has killed around 160,000 rainbow trout from three hatcheries, located outside Klamath Falls, Roseburg and Port Orford, to prevent the spread of a myxozoan parasite.
The organism is known to be present in the Pacific Northwest but this is the first time it has been blamed for causing illness in Oregon’s fish stock. The microscopic parasite commonly infects a worm before moving to a fish, where it can cause illness and death. Scientists hypothesized a species of that organism killed off tens of thousands of Montana salmon in 2016.
Oregon State University and ODFW researchers are examining a sample of 500 sick trout to learn more about how and when those fish may have been infected. There are some 2,400 different species of myxozoa. The agency doesn’t yet know which infected these fish.
“We're hoping we can find out more about it because with the change in climate, warmer rivers — those conditions favor pathogens. It may be that we see this or something else again,” said Michelle Dennehy, spokesperson with the Oregon Department of Fish and Wildlife.
Dennehy said her agency’s fish health lab, which monitors the spread of pathogens, has become increasingly important as a “first line of defense” against possible contagions.
The agency raises and releases around 3.8 million rainbow trout per year for fishing and has over 100,000 surplus stock to make up for losses. So anglers shouldn’t notice a difference this year, said Dennehy.
She said her department will also be reviewing hatchery infrastructure to find better ways to keep fish populations healthy.
