Fatal Bacterial Disease Found in B.C. Wild Salmon

Emiliano Di Cicco, a researcher with the Pacific Salmon Foundation, stated that the condition had never been observed previously in Pacific salmon.

Understanding Tenacibaculosis in Wild Chinook Salmon

The bacterial disease causes severe ulcers on a salmon’s mouth, skin, and fins. According to Emiliano Di Cicco, infected fish also exhibit abnormal behavior, including lethargy, loss of balance, and abnormal swimming. The illness leads to death within a few days. During two studies comprising 99 sampled fish, researchers recorded a 16 percent mortality rate among individuals showing signs of the infection.

Tenacibaculosis stems from a common marine bacterium known as Tenacibaculum dicentrarchi. While well-documented in farmed Atlantic salmon where it appears in high concentrations around global fish farms, the bacterium had not previously been found in wild-caught Pacific salmon. Outbreaks in aquaculture typically occur when juvenile fish transition from freshwater to saltwater.

Accidental Discovery During UBC Research

Researchers stumbled upon the disease by accident during a 2022 field study. Within days, sampled fish began developing lesions directly in front of their tails before dying.

The field team contacted the Pacific Salmon Foundation to investigate the mortalities. Through subsequent analysis, Emiliano Di Cicco and his colleagues identified tenacibaculosis as the likely cause of mortality. Because diseased fish in aquaculture are easily monitored inside cages, tracking the illness in the wild has remained very hard.

Potential Impacts on Endangered Southern Resident Orcas

The confirmation of the disease in wild fish has raised alarm among marine mammal observers. Mark Malleson, lead skipper with Prince of Whales, called the finding concerning. Because southern resident orcas rely on wild chinook salmon for their livelihood, Malleson noted that any factor contributing to wild chinook declines could lead to more southern resident orca loss.

However, the Pacific Salmon Foundation views the disease as one of many potential contributing factors facing salmon population rates, alongside water temperatures and habitat loss. Emiliano Di Cicco noted that the disease should be kept in mind and managed as best as possible based on current knowledge.

Regulatory Gaps and Next Steps for Fisheries Management

Emiliano Di Cicco stated that this evidence is not currently accounted for in Fisheries and Oceans Canada’s existing disease risk assessment. To address these gaps, researchers are conducting further research to trace the origin of the bacteria, determine how wild chinook acquire the pathogen, and chart its development.

Gaining a clearer picture of transmission routes will allow management agencies to better understand how to protect wild salmon populations along the British Columbia coast.

Frequently Asked Questions

What is tenacibaculosis?

Tenacibaculosis is a bacterial disease caused by Tenacibaculum dicentrarchi that triggers skin ulcers, fin damage, and rapid mortality in fish.

How was the disease discovered in wild salmon?

Researchers sampling wild chinook salmon for a study on recreationally caught and released salmon in 2022 noticed unusual tail lesions and dying fish, prompting analysis by the Pacific Salmon Foundation.

Are farmed salmon the source of the bacteria?

While the bacterium is found in high concentrations at fish farms and is well-documented in farmed Atlantic salmon, researchers are still investigating exactly how wild chinook acquired the pathogen.