A week after grabbing headlines with their sensational claims to bolster anti-salmon farming activism in Canada, researchers who claimed that the PRV virus spread from aquaculture operations into wild fish, have gone silent.
By Fabian Dawson
Globally renowned fisheries experts are questioning a recently released study by the University of BC (UBC) about the origins and impacts of a benign virus, which claims spread from salmon aquaculture operations into wild fish.
A week after grabbing the headlines with their sensational claims to bolster anti-salmon farming activism in Canada, the UBC study authors have gone silent, refusing to answer questions put forward by aquaculture experts.
The researchers said they used genome sequencing to trace the piscine orthoreovirus, or PRV, concluding that it was first introduced to B.C. waters from Norway about 30 years ago at the start of open-net pen aquaculture in the province.
They then expanded on previously debunked analysis and went on to say PRV is now an important infectious agent in critically endangered wild Pacific salmon populations.
“As a board-certified veterinary pathologist, I disagree with the conclusion that PRV is now an important infectious agent in critically endangered wild Pacific salmon populations,” said Dr. Gary Marty, a veteran fish pathologist with the Animal Health Centre of BC’s Ministry of Agriculture, Food, and Fisheries.
The earliest positive PRV test result was from a wild-source steelhead trout sampled in 1977, which predates salmon farming in BC, said Dr. Marty. This documented test result was not used by the UBC researchers, to reach their current conclusion.
PRV has long been present in wild salmon in Pacific Northwest waters and all experimental exposures of the BC strain of PRV to Pacific and Atlantic salmon in BC have failed to induce disease or mortality, according to consensus by a broad range of fisheries scientists.
The UBC study reflects this fact but the researchers, known for their anti-salmon farming stance, have kept it largely hidden from their public presentations.
“PRV is a minor infectious agent that occurs in a small proportion of wild Pacific salmon,” said Dr. Marty.
“Even the thesis cited by the new paper reports only mild PRV-associated microscopic lesions among six of nine wild Chinook salmon examined. The other three fish had no PRV-associated microscopic lesions.
“Mild microscopic lesions are not a threat to wild salmon populations. Instead, mild lesions are part of the normal inflammatory response to infectious agents that wild fish encounter during their migrations,” he said.
“The idea that salmon farms shed PRV into the environment is not new. The idea that the BC strain of the PRV came from Norway is not new”
Cutting through the noise generated by the UBC study, Dr. Hugh Mitchell, an aquaculture veterinarian, with more than 30 years of experience, said the paper has more to do with activism against fish farms than science.
In a Twitter post, Mitchell states: “First, PRV was found in 1977 AND sequenced from wild-source BC steelhead trout pre-dating Atlantic salmon PNW (Pacific North West) culture. Allegations of being introduced by farmed Atlantic salmon are false.
“Secondly, the virus does not sicken fish. Controlled challenge laboratory studies consistently show no clinical disease can be produced in Sockeye or Chinook salmon. Furthermore, Federal, State and Tribal hatchery managers have never viewed it as important amongst the myriad of bacteria, viruses and parasites that are a natural part of wild salmon populations. In the ocean, where there are 150 billion viruses in a teaspoon of seawater, there are far more critical pathogens.
“What is disturbing is that the paper’s authors are an isolated group (not representative of the entire Canadian Department of Fisheries and Oceans) who continually focus on activist research against aquaculture and ignore contradicting evidence.
“Agriculture was necessary to lessen the impact on the environment while feeding humanity. Aquaculture does the same for the oceans. We need to quit with this bickering and catch up with the rest of the world on the ‘blue revolution’.”
This is not the first time assertions by a group of activist-scientists have come under scrutiny after they are published and promoted by the anti-fish farm lobby.
Last April, they quietly corrected their study which suggested wild stocks exposed to marine aquaculture sites have much higher rates of viral infection.
The correction to their original 2017 study, which was posted in the journal PLOS ONE, dismantles claims by the activists that the abundance of the piscine orthoreovirus (PRV) in wild fish is related to exposure to salmon farms.
Another group of activist-scientists published a paper in 2011 titled “Lethal Atlantic virus found in Pacific salmon”. That paper was also proven to be false leading to the laboratory that did the screening work to lose its international accreditation.
The Minister of Fisheries and Oceans then stated, “because some have chosen to draw conclusions based on unconfirmed information, this has resulted in British Columbia’s fishing industry and Canada’s reputation being put at risk needlessly.”
The activist-scientists were also warned by the BC Government and Fisheries and Oceans Canada that reckless allegations based on incomplete science can be devastating and unfair to the families that make a living from the sea.
Dr. Ian Gardner, Canada Excellence Research Chair in Aquatic Epidemiology, who is part of the Strategic Salmon Health Initiative (SSHI) has described the PRV studies by the activists as making “broad sweeping statements not supported by evidence.”
Dr. Kenneth Warheit, fish health and genetic specialist for the Washington Department of Fish and Wildlife has said activists have failed to find a single study to support the claim that PRV from open-water pens will harm wild fish.
Kyle Garver a research scientist for Fisheries and Oceans Canada and a PRV expert has also concluded that PRV has been ubiquitous in the Pacific Northwest for many decades, and that it isn’t linked to any fish disease or mortality.
The virus does not kill sockeye salmon or Atlantic salmon, the Canadian Science Advisory Secretariat (CSAS), which reviewed Canadian and international PRV data, concluded.
Two other studies found that the strain of PRV found in B.C. fish to be benign. The first, 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.
“Through archived salmon tissue samples from 1977, there is evidence that PRV existed in BC waters long before the establishment of salmon farms,” said the BC Salmon Farmers Association (BCSFA).
“There is also evidence that the strain of PRV found in BC waters is genetically different than those found in Europe. The BC strain has been found to be asymptomatic – in that it does not cause disease in wild or farmed salmon…There have been numerous studies done on this front
“We are not importing anything. The Atlantic salmon we farm in BC is 100 per cent BC grown. Our fish are raised in hatcheries on Vancouver Island, from brood stock born and raised on Vancouver Island. Before our fish are transferred to our ocean sites, they go through several health checks and are vaccinated against several known diseases,” said BCSFA in a statement.
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.
(Image courtesy of Grieg Seafood shows fish farmers monitoring net pens with underwater cameras)