Scientists discover a disease in wild B.C. salmon previously only found in farmed fish
A new study reveals that some wild B.C. salmon have been discovered with a disease previously only found in farmed fish.
Researchers from the University of British Columbia (UBC) and the Pacific Salmon Foundation (PSF) found a bacterial disease in several wild Chinook salmon known as tenacibaculosis, which causes skin and fin ulcers and fish mortality.
In 2022, UBC scientists were working on an entirely different study on the impacts of catch-and-release, in B.C.’s Barley Sound on the west coast of Vancouver Island. But a few days into the study, they noticed “unusual bacterial lesions developing on some of the fish,” said Katie Zinn, with UBC’s Pacific Salmon Ecology and Conservation Lab, and co-author of the study, in a release.
“We spend enormous effort trying to understand why wild salmon die in the ocean. This study gives us one of the clearest pieces of evidence that links bacterial disease to mortality in wild Pacific salmon,” said Zinn.
Emiliano Di Cicco/Pacific Salmon Foundation
UBC then started working with PSF, Fisheries and Oceans Canada (DFO)’s Pacific Biological Station, the University of Toronto, and the University of California, Davis. They determined that it was likely caused by a common type of marine bacterium called Tenacibaculum dicentrarchi.
“This is the first time tenacibaculosis has been diagnosed in wild-caught fish, providing empirical evidence that Tenacibaculum bacteria can negatively affect wild fish health and contribute to disease burden in B.C. wild salmon,” said Emiliano Di Cicco, a fish health researcher with the PSF and lead author of the study, in the release.
Di Cicco added that it is challenging to diagnose marine diseases in wild fish, since they often die quickly.
“Once a wild fish gets sick, it’s often caught by a predator quickly, or it becomes too weak to feed and eventually starves. That’s why finding a sick fish in the wild is so difficult,” he said.
PSF noted these findings provide new evidence that the DFO doesn’t account for in their existing disease assessment for Tenacibaculum maritimum, a closely related bacterium to Tenacibaculum dicentrarchi.
“As a result, these bacteria are currently not regulated in British Columbia as a risk to wild Pacific salmon, while other Tenacibaculum species (like T. dicentrarchi) are not even considered in the assessment.”
PSF said that tenacibaculosis is one of the most common diseases in farmed Atlantic salmon raised in open-net pens in B.C., and the leading cause of farm mortality.
“Common symptoms include lethargy, loss of balance, abnormal swimming behaviour, skin, fins and oral ulcers, and high mortality,” reads the press release.
Researchers noted that handling the fish during the capture and holding stages might have increased their vulnerability to infection, since their protective mucus layer on their skin and fins might have been damaged.