RESEARCH MATTERS
The infectious fallout of raising Atlantic salmon in the Pacific
Salmon Steward: Winter 2021
Piscine orthoreovirus (PRV) is continually being transmitted between open-net salmon farms and wild juvenile Chinook, according to new genomics research jointly supported by the University of British Columbia and the Strategic Salmon Health Initiative.
The study, published in Science Advances this past May, highlights the role of salmon farming in introducing novel pathogens to new regions, where they then spread to wild fish. The research found evidence that farming Atlantic salmon in Pacific waters introduced PRV to the region, and that PRV is now exceedingly common on B.C. salmon farms, and is then passed on to wild fish.
The study used virus surveillance and genomic sequencing to reveal that:
- PRV originates from Atlantic salmon farms in Norway, thus supporting the wide consensus established by previous research.
- Today, the virus is almost ubiquitous in B.C. salmon farms.
- Wild Chinook caught closer to salmon farms are more likely to be infected with PRV. Additionally, both wild and farmed salmon with PRV are infected by the same variants of the virus. Considered together, these two findings indicate that viral spillover from farms to wild salmon continually occurs.
- The ancestor of the PRV lineage currently in B.C. salmon arrived roughly 30 years ago. This suggests that the introduction of PRV to B.C. and infection of wild Pacific salmon is a relatively recent phenomenon and coincides with the arrival of Atlantic salmon aquaculture in the region.
- The number of PRV infections in British Columbia has grown in recent decades, corresponding with the regional growth in salmon aquaculture and high rates of viral infection in salmon farms.
“There has been much confusion about where PRV is originally from and whether it is transmitted between farmed and wild salmon,” says Dr. Gideon Mordecai, a viral ecologist at UBC, who led the study. “This study’s genome sequencing clearly indicates PRV is not native to B.C. waters – it originated in the Atlantic Ocean and has been spread around the world through salmon aquaculture.”
The Strategic Salmon Health Initiative is a partnership between the Pacific Salmon Foundation, Fisheries and Oceans Canada, and Genome BC. Dr. Gideon Mordecai was funded by the Liber Ero Fellowship.
Viral Consequences.
PRV triggers Heart and Skeletal Muscle Inflammation (HSMI) in Atlantic salmon. A recent Norwegian study found that a B.C. isolate of the virus causes heart lesions in Atlantic salmon. More relevant to Pacific salmon, research led by PSF scientist Dr. Emiliano Di Cicco found that PRV is associated with jaundice/anemia in Chinook, a potentially fatal disease that results from red blood cells bursting, leading to liver and kidney damage.
“There has been much confusion about where PRV is originally from and whether it is transmitted between farmed and wild salmon,” says Dr. Gideon Mordecai, a viral ecologist at UBC, who led the study. “This study’s genome sequencing clearly indicates PRV is not native to B.C. waters – it originated in the Atlantic Ocean and has been spread around the world through salmon aquaculture.”
The Strategic Salmon Health Initiative is a partnership between the Pacific Salmon Foundation, Fisheries and Oceans Canada, and Genome BC. Dr. Gideon Mordecai was funded by the Liber Ero Fellowship.
Cover photo: PSF salmon scientists Dr. Emiliano Di Cicco and Dr. Andrew Bateman study the connection between aquaculture and the spread of pathogens. Photo by Amy Romer.
