Wild salmon pathogens discovered that could pose a threat to aquaculture

Three new viruses – including one type that has never previously infected fish – have been identified in populations of both wild and farmed salmon off the coast of British Columbia, Canada.

Researchers from the University of British Columbia and Fisheries and Oceans Canada have identified three new viruses that are impacting populations of endangered salmon in the North Pacific. They used DNA sequencing and virus-specific tests to screen more than 6,000 dead and dying salmon in the wild, in hatcheries and on fish farms. Sampling from three different cohorts allowed the researchers to determine the distribution of the virus.

Two of the viruses were found in wild, hatchery and cultured salmon. One virus was found in farmed adult salmon. This finding is notable because it suggests that the viruses are distributed differently among the Chinook and sockeye salmon populations. It also suggests that the virus has a different route of transmission within and between populations of farmed, wild and hatchery salmon.

"We found the new viruses widely distributed in dead and dying farmed salmon and in wild salmon," UBC virologist Curtis Suttle told phys.org. "It emphasises the potential role that viral disease may play in the population dynamics of wild fish stocks, and the threat that these viruses may pose to aquaculture."

Populations of sockeye and Chinook salmon have been declining for the past 30 years. A potential contributor to their decline could be viral infection. These populations of salmon play a critical role in Canada’s Pacific ecosystem, making their conservation a long-term goal and high priority. The species have supported the Indigenous population for thousands of years and are a key element of Canada’s aquaculture strategy.