New studies reaffirm PRV is not a salmon killer

Two new scientific studies dismantle key claims made in court by fish farm opponents.

By Fabian Dawson

Two new studies have reaffirmed that the piscine reovirus (PRV) is not a salmon killer in British Columbia, dismantling key claims made in court by fish farm opponents.

The studies come in the wake of Ottawa’s decision not to appeal a Federal Court ruling last February, that struck down a Department of Fisheries and Oceans (DFO) policy on the transfer of baby salmon to the ocean environment.

Anti-fish farm activist Alexandra Morton along with the ‘Namgis First Nation had sued DFO claiming that salmon smolts being introduced to open pen facilities needed to be screened for the virus.

They claimed the virus causes disease in salmon, despite the volume of existing peer reviewed scientific evidence that finds PRV does not cause disease in fish in the Pacific.

The court gave DFO four months to review the science and develop a new policy but it did not give any guidance on what that policy should be or if the new policy should include screening for PRV.

“The Government of Canada has completed its review of the February 4, 2019 Federal Court ‘Namgis decision. We will not be appealing,” A DFO statement said.

The statement pointed to a segment of the court’s ruling that said “it is possible that the Minister will still conclude that it is appropriate to maintain the PRV Policy,” or in other words, that it is not necessary to test for Piscine Orthoreovirus (PRV).

DFO also clarified two misrepresentations of the court ruling made by those opposed to open net fish farming.

“The Court did not order DFO to test for PRV prior to authorizing transfers of smolts to aquaculture facilities, or prior to releasing smolts in the wild. The Court also did not make any decision or statement concerning whether the failure to test for PRV in hatchery smolts poses a risk to wild salmon,” the DFO said.

This week, two new published studies confirmed what was already previously concluded by other scientific analysis – that the claims about PRV by the anti-fish farming lobby are grossly exaggerated.

One study, published in Scientific Reports, was conducted by scientists from the Pacific Biological Station and the provincial government’s Animal Health Centre.

The other, published in Frontiers in Physiology, was conducted by scientists at the University of BC and the Pacific Biological Station.

The studies found that the strain of PRV found in B.C. fish to be benign.

The respiratory systems of Atlantic salmon function normally even when carrying large loads of PRV, the UBC research found.

“We didn’t find significant harm to the fish’s respiratory physiology despite the virus replicating to a load equal to, if not higher, than those seen naturally in wild or farmed fish” said Yangfan Zhang, a PhD student in UBC’s faculty of land and food systems and lead author of the study published today in Frontiers in Physiology.

“Consequently, the results are a positive step in reducing the uncertainty about the potential of infected farmed Atlantic salmon in marine pens to negatively impact migrating wild Pacific salmon.”

The researchers performed their 21-week experiment on groups of juvenile Atlantic salmon obtained from a commercial hatchery on Vancouver Island and recently transferred to seawater. One group was injected with a dose of PRV that was high enough to represent a worst-case infection scenario.

The scientists used respirometry–not unlike the VO2 max test undertaken by elite athletes–to measure how efficiently oxygen was taken up and transported by the salmon’s cardiorespiratory system. They also measured 13 other indicators, such as the fishes’ ability to recover from exertion, whether they were settled or active in the testing chamber, and their ability to perform anaerobic tasks.

They found no physiological differences between the infected fish and fish from a control group, a result that highlights the distinction between a virus being prevalent and being virulent. Prevalence refers to how widespread a virus is among a population; virulence refers to the damage it causes. While most people equate viral infection with disease, in the case of the B.C.-farmed Atlantic salmon, one did not necessarily lead to the other.

“Besides no sublethal effects of a ‘full-on’ PRV infection, none of our fish died and none developed severe inflammation of the heart. These data show that there is minimal risk of ensuing problems from the B.C. strain of PRV to B.C. farmed Atlantic salmon,” said Tony Farrell, a professor in UBC’s faculty of land and food systems and a principal investigator of the research team. (pictured courtesy of  ReachOutReachOut Faculty of Land and Food Systems at UBC.)

The authors have performed a similar experiment on wild sockeye salmon with similar results, which they are now compiling for publication.

“These findings are consistent with the large body of science done indicating the strain of PRV found off B.C.’s coast is different from the one found in Norway, and the risk to wild and farmed salmon is minimal,” said Shawn Hall, a spokesman for the B.C. Salmon Farmers Association.

“The science indicates that responsibly-farmed salmon and wild salmon populations can successfully coexist in our oceans,” he said.

“Our industry has long supported research and science into the health of both wild and farm-raised salmon, from the ongoing Cohen commission risk assessments to broader Bering Sea studies, to assist in understanding the challenges wild salmon face.”

“Salmon farming is important in B.C., providing about three-quarters of the salmon harvested in our province each year, and thus helping protect wild salmon from over-fishing. It also supports almost 7,000 jobs,” added Hall.

Question and Answer: Piscine Reovirus (PRV)

What is PRV?

Piscine reovirus is a virus that can infect Atlantic and Pacific salmonids. Reoviruses get their name because many are respiratory and enteric orphans. They are called “orphans” because many are viruses without an associated disease.

Is PRV found in British Columbia?

Yes. Research published in 2014 suggests PRV has long been present in wild salmon in Pacific Northwest waters.

What impact does PRV have on salmon?

PRV has been detected in healthy fish in healthy populations, showing that its presence does not mean disease occurs.

But isn’t a virus a disease?

No. Not all germ’s in our environment cause disease. There are millions of viruses in every drop of seawater. Viruses are carried by all living things and most never cause disease. Other reoviruses have been found for decades in wild fish and never associated with disease. In British Columbia, there is no link between the presence of PRV and any disease.

Do salmon farmers test for PRV?

Yes. BC salmon farmers provided samples for the 2014 scientific study that documents PRV in BC and Alaska salmon without associated disease. BC salmon farmers are providing samples for other scientific studies that are underway. This is being done even though Fisheries and Oceans Canada (DFO), and the Canadian Food Inspection Agency (CFIA), do not have PRV on the list of reportable diseases/pathogens.

What about the suggested link between PRV and heart and skeletal muscle inflammation (HSMI)?

That link refers only to Norwegian strains of PRV in farmed Atlantic salmon. HSMI is common in Norway, but HSMI has never been identified in any wild fish in the Pacific Northwest. Viruses with the same name often occur as different types in different parts of the world. Some types might cause disease whereas others do not. PRV is a good example.

Is there any human health risk associated with PRV?

No. Viruses found in salmon (including PRV) are not a risk to human health.


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