UBC Study Examines Fitness of Pacific Sockeye Salmon Infected with PRV

A new study from the University of British Columbia in Vancouver, BC, finds that the respiratory performance of wild Pacific sockeye salmon is normal even when infected with piscine orthoreovirus (PRV).

The findings by UBC researchers, with partners from the Department of Fisheries and Oceans Canada and Ministry of Agriculture, Food and Fisheries, were published in BMC Biology.

According to UBC post-doctoral researcher Yangfan Zhang, joint lead author of the study, researchers 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.

The nine-week study found no physiological differences between PRV-infected fish and a control group injected with a salt solution. This, Zhang said, means that PRV poses a very low risk to B.C.s population of wild Pacific salmon. According to DFO researcher Mark Polinski, the joint lead author, these findings highlight that not all animal viruses cause notable harm during infection.

PRV infects most farmed Atlantic salmon and a small proportion of wild Pacific salmon, the researchers said. The study used sockeye salmon to test the respiratory impacts of wild salmon because they migrate near salmon farms. The experiment was conducted on 400 sockeye salmon at the DFO Pacific Biological Station at Nanaimo, BC.

One group of sockeyes were injected with a dose of purified PRV to induce a high-dose infection scenario another with a saline solution, and another 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. Still, researchers noted IHNV triggered 30% mortality and a temporarily reduced maintenance metabolism, although survivors were able to resolve the infection within weeks, they said.

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.

They concluded that Pacific and Atlantic salmon can resist a PRV infection without a major metabolic cost.