Apocalyptic fearmongering by anti-salmon farming activists dismantled by new scientific study
By Fabian Dawson
A new scientific study has dismantled the bogus claims by anti-aquaculture activists, that the piscine reovirus (PRV) is a salmon killer and will devastate the iconic species in British Columbia.
The study, like the ones before, refutes core apocalyptic fearmongering by the activists who tell their mainly urban followers that PRV, allegedly spread from fish farms, cause diseases in wild salmon stocks.
PRV has long been present in wild salmon in Pacific Northwest waters and has been detected in healthy fish, showing that its presence does not mean disease occurs.
Despite the fact that viruses found in salmon (including PRV) are not a risk to human health or wild stocks, the anti-fish farming lobby has mobilised a campaign to oust net-pen farmers in BC, who support 6,500 jobs near rural and remote Vancouver Island, Central Coast, and Sunshine Coast communities.
The latest study by researchers at University of BC, Fisheries and Oceans Canada (DFO) and the Ministry of Agriculture, Food and Fisheries found respiratory performance of wild Pacific sockeye salmon functions normally even when infected with piscine orthoreovirus (PRV).
The findings are published in BMC Biology.
“We saw little to no effect on sockeye salmon’s respiratory fitness after PRV-infection and minimal impacts on their ability to sustain the vigorous activity needed to migrate, catch prey and avoid predators,” said Dr. Yangfan Zhang, a post-doctoral researcher in UBC’s faculty of land and food systems and the department of zoology, and the joint lead author of the study.
The nine-week study found no physiological differences between PRV-infected fish and a control group, injected with a salt solution.
“This means PRV poses a very low risk to British Columbia’s population of wild Pacific salmon,” Dr. Zhang said.
“The findings highlight that not all animal viruses cause notable harm during infection,” said joint lead author, Dr. Mark Polinski, a DFO researcher.
PRV infects most farmed Atlantic salmon and just a small proportion of wild Pacific salmon. The study used sockeye salmon to test the respiratory impacts of wild salmon because they migrate near salmon farms.
“This is the first study to show that sockeye salmon can be a carrier of PRV without untoward physiological effects to their respiratory system,” said Dr. Tony Farrell, a professor and Canada Research Chair with UBC’s faculty of land and food systems and the department of zoology, and one of the principal investigators on the study.
The research team ran their experiment on a total of 400 sockeye salmon at the DFO Pacific Biological Station in Nanaimo, BC.
One group of sockeye salmon was injected with a dose of purified PRV to induce a high-dose infection scenario, another with a saline solution, and a third group was injected with the more virulent infectious hematopoietic necrosis virus (IHNV) in a separate positive-control study.
None of the salmon died while carrying the PRV infection. But researchers noted IHNV triggered 30 per cent mortality and a temporarily reduced maintenance metabolism, although survivors were able to resolve the infection within weeks.
Researchers also measured the ability of red blood cells infected with PRV to bind oxygen, as well as the metabolic rate – or oxygen uptake – of infected salmon, to evaluate their ability to maximally use oxygen, recover from exhaustion, and function when oxygen is low.
“The experimental PRV infection of sockeye salmon shows that the virus had no substantial impact on their oxygen use during maximum exercise, or when oxygen is low,” Dr. Farrell said.
“Pacific and Atlantic salmon can resist a PRV infection without a major metabolic cost,” he said, addressing those concerned about the untested impacts of PRV on wild sockeye salmon.
The authors previously performed similar investigations with PRV-infected farmed Atlantic salmon with similar results, published in 2019.
The UBC researchers worked with scientists from the BC Ministry of Agriculture, Food and Fisheries, and Fisheries and Oceans Canada—which funded the study—with collaborative support from the BC Salmon Farmers Association (BCSFA) who did not participate in the study design, data collection, and analysis, preparation of the manuscript, or decision to publish.
In 2019, two similar studies found that the piscine reovirus (PRV) is not a salmon killer in British Columbia,
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.
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 viruses 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 a 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 of Dr. Yangfan Zhang courtesy of University of BC)