Deadly Parasite Ceratonova Shasta Devastates Chinook Salmon in Klamath River

A deadly parasite is killing fish in a major river running through California and Oregon, according to reports. The parasite is known as Ceratonova shasta and is thought to be the reason behind a high number of dead and dying Chinook salmon appearing both in traps and along the Klamath River.

"What we get concerned about is when those infections develop into severe infections and disease, and when that disease culminates in premature death of these fish," Sascha Hallett, an assistant professor at Oregon State University, told SFGATE.

According to Hallett, severely ill fish typically die before the parasite can mature. However, in this case, officials are detecting sick and dead fish containing mature parasites that can lead to new infections.

"It’s unusual that there’s such a severe reaction and the parasite has still been able to mature," Hallett said.

When in spore form, the parasite latches onto a fish’s gills and causes hemorrhaging. It finishes its lifecycle by infecting tiny freshwater worms that release spores, and the cycle repeats.

Ceratonova shasta is not deadly to humans.

On June 1, the U.S. Fish and Wildlife Service announced that 46 percent of the nearly 700 juvenile salmon tested by their researchers were positive for Ceratonova shasta.

According to Hallett, record-low snowpacks in Northern California and Oregon have led to lower snowmelt in the river this spring. As a result, the river is running warmer and at lower water levels than in previous years.

When the water becomes too warm, Chinook salmon become stressed and are less capable of dealing with infections, Hallett said. Those warmer temperatures could also be aiding the rapid proliferation of the parasite.

Peter Tira, a spokesperson for the California Department of Fish and Wildlife, told SFGATE that 675,000 juvenile salmon were released into the Klamath River in May. The fish, which were screened for disease, were released right before storms that would cool the water and raise the water level.

However, Stephen Atkinson, an assistant professor of microbiology at Oregon State University, told the publication that the juvenile salmon remained in the same area for a few days before moving out to the ocean. While remaining in that warmer water, these fish could have been exposed to the parasite spawn.

Atkinson also confirmed that researchers detected another parasite, Parvicapsula minibicornis, that could be sickening fish in the river.

In recent years, four major dams have been removed from the Klamath River. According to a press release from California Governor Gavin Newsom’s office, that effort has restored nearly 400 miles of habitat for salmon and other species.

Now, the river is in “transition,” Hallett says, with the parasite now reaching farther north than ever before. Officials did not anticipate the parasite to be “so abundant so quickly,” she said.

Hallett, though, confirmed that experts are monitoring the situation over the upcoming weeks and assessing whether the parasite was the leading cause of death for the fish.

"We just don’t have the complete picture yet," she admitted.