Heart and skeletal muscle inflammation found at five of seven B.C. open-net salmon farms studied, researchers say

Viral heart disease is more widespread in open-net salmon farms in British Columbia than earlier farm audits suggested, according to a new peer-reviewed study from the Pacific Salmon Foundation published in the journal Aquaculture and reported by CBC News. Researchers found heart and skeletal muscle inflammation, or HSMI, at five of seven open-net pen Atlantic salmon farms in the Broughton Archipelago, east of Port McNeill on Vancouver Island.

Lead author Emiliano Di Cicco said the team examined 749 salmon with three independent pathologists and found that nearly seven per cent showed signs of HSMI. “We found the occurrence of the disease is much higher than what was thought previously,” Di Cicco told CBC. A 2017 study by Di Cicco and colleagues had identified the condition at one of four farms; “Now we have evidence that that was really not the case,” he said of treating that earlier result as an isolated event.

The study links HSMI to piscine orthoreovirus, or PRV, and says the virus can move into surrounding waters and infect wild fish, CBC reported. Pacific salmon infected with PRV can develop anemia, inflamed hearts, damaged livers and kidneys, and jaundice, according to the researchers cited by CBC. Di Cicco argued Fisheries and Oceans Canada still classifies the B.C. strain of PRV as non-pathogenic and wants that designation changed, along with diagnostic criteria that he says miss chronic, low-level cases.

Fisheries and Oceans Canada’s PRV and HSMI overview says PRV genetic material has been detected in Pacific-coast salmonids dating back decades and that experimental exposures of the B.C. strain have so far failed to induce disease or mortality in Pacific and Atlantic salmon in B.C., suggesting low virulence in those trials. DFO notes HSMI is diagnosed from heart and skeletal-muscle lesions and that factors beyond PRV may be required for disease to develop.

In a statement to CBC, DFO said it will review the new study. “Detecting a virus or disease in farmed fish does not, on its own, demonstrate impacts on or decrease of wild salmon populations,” the department said. It added that Canadian and international veterinarians and pathologists produced the current HSMI case definition in January 2020 to align with global standards. The B.C. Salmon Farmers Association did not immediately comment to CBC; the industry has previously described PRV concerns as overstated.

The findings land amid Canada’s planned phase-out of open-net pen salmon aquaculture in B.C. by 2029. The Pacific Salmon Foundation says roughly 55 farms remain licensed or operating after about 45 closures, and that peer-reviewed work on pathogens and parasites continues to inform the transition. Di Cicco told CBC that if regulators wait for large mortality spikes before diagnosing HSMI, “most likely you are going to miss it.”

This article is general science reporting and is not medical advice.

Sources: CBC News (Oct. 11, 2026); Fisheries and Oceans Canada: Piscine Orthoreovirus (PRV) and Heart and Skeletal Muscle Inflammation (HSMI); Pacific Salmon Foundation: The latest on open-net pen salmon farms in B.C..