Newly published research says that piscine orthoreovirus (PRV) doesn’t cause severe heart inflammations in farmed Atlantic salmon in B.C., and their respiratory fitness is unaffected by the virus.
The two DFO-funded studies published online by peer-reviewed journals on Wednesday represent the latest developments in the controversy surrounding PRV.
The research suggests that PRV is less of a threat for Atlantic salmon in B.C. than in Norway, where it causes a deadly condition known as heart and skeletal muscle inflammation (HSMI).
“The PRV here, at least in our B.C. salmon, seems to have a lower capacity to cause disease than it does in Norway,” says Mark Polinski, co-author of the two studies and research scientist with Fisheries and Oceans Canada (DFO).
The virus infects Atlantic salmon throughout B.C. and is also found among wild Pacific salmon.
PRV-infected Atlantic salmon with severe heart inflammations turned up during audits on B.C. fish farms in recent years, and researchers wanted to know whether the virus was causing that HSMI-like condition.
Researchers injected Atlantic salmon with the virus, and compared those fish with a virus-free control group. They found the virus didn’t cause severe heart inflammations, although cases of minor inflammations increased, Polinski said.
The other study – written by scientists from DFO and the University of British Columbia and published online by the journal Frontiers in Physiology – found that PRV didn’t affect the cardiovascular and respiratory fitness of farmed Atlantic salmon.
For the experiment, PRV-infected farmed B.C. Atlantic salmon were placed in a testing chamber with an oxygen sensor that measured the efficiency of their respiratory systems compared to virus-free fish.
“We get a new measure every ten minutes, and we do that for five days,” Polinski said.
Various indicators were measured, including recovery from exertion. The experiments showed no significant differences between infected and non-infected fish, Polinski explained.
While these tests involved Atlantic salmon, he added that tests on wild sockeye showed similar results, although those findings haven’t yet been published.
Previous research indicates a connection between PRV and anemia in chinook salmon in B.C. The new studies don’t have any bearing on that research, Polinski said.
Asked why the two peer-reviewed articles were released on the same day, he said the Frontiers in Physiology article relied on research in the Scientific Reports article, so the former was held until the latter’s publication. Both studies were funded through grants from DFO.
This follows a series of events that have renewed scrutiny on the virus and its effects.
On Feb. 4, a Federal Court judge struck down a DFO policy allowing fish farm companies to transfer young Atlantic salmon into open-net pens without first screening them for PRV, saying the threshold for harm to wild stock was too high and the precautionary principle wasn’t met.
The court also ruled that Ottawa breached its duty to consult ‘Namgis First Nation about PRV policy.
The decision came in response to lawsuits brought forward by ‘Namgis First Nation and marine biologist Alexandra Morton, a prominent critic of the fish farm industry.
DFO said on Tuesday that it won’t appeal the decision. DFO’s court-ordered review of PRV policy is ongoing.
On the heels of the Feb. 4 ruling, DFO announced that participants in an expert peer-review process had reached a consensus that PRV poses minimal risk to Fraser River sockeye salmon.
That led to controversy when someone involved in that process – John Werring of the David Suzuki Foundation – said that no consensus exists, and that too much uncertainty remains about the pathogen and how it spreads.
PRV is just one bugbear for B.C.’s controversial aquaculture industry.
Opponents of open-net fish farming have long argued that salmon farms discharge harmful materials and contaminate the environment, spread sea lice and diseases among wild fish, and allow Atlantic salmon to escape, posing a variety of risks to wild stocks sacred to First Nations.
Industry critics have called for the removed of fish farms from B.C. waters. Alaska has banned open-net fish farms, while Washington State has begun phasing out its Atlantic salmon facilities, leaving B.C. as the hold-out in the Pacific Northwest.
Industry officials and other proponents say that concerns about fish farms are overblown and that open-net aquaculture provides a relatively green source of food, lowers pressure on wild stocks and provides economic benefits to B.C.
According to a study commissioned by the BC Salmon Farmers Association – which represents the fish farm industry – more than 2,900 people were employed directly in salmon farming by 2016.
Another 3,600 workers were either employed indirectly – that is, by industry suppliers – or due to spending by workers in the industry, according to the study.