Aquaculture North America

OAA 2024: Ontario ministry vet identifies fish health threats to be wary

March 21, 2024
By Seyitan Moritiwon

Alexandra Reid, lead veterinarian animal health and welfare, at Ontario Ministry of Agriculture, Food and Rural Affairs said to be proactive about fish health, Ontario farmers must talk about them.

At the Ontario Aquaculture Association conference in Orillia, Ont., Canada, Reid gave a presentation on Fish health threats that might scale up in Ontario and how they can be tackled. About 150 aquaculture professionals and students were in attendance at the conference that took place at the Fern Resort on March 19-21.

Viral hemorrhagic septicemia virus: Reid said this disease is everywhere and affects a ton of native species. There are a ton of different genotypes but the one that is of major concern in North America is genotype IV. “One of our concerns is as we move into more native species, we’re interested in raising native species, this disease picture changes and they become quite susceptible. So we still don’t know a lot about it. And there’s always the potential that things can change,” she said.

Infectious pancreatic necrosis virus: It’s one of the most environmentally stable and resistant fish pathogens around. It’s resistant to drying, it’s resistant to temperatures, it’s resistant to a lot of disinfectants. 

“Our concern is really that Quebec is in the middle of a huge outbreak. They think they have persistently infected broodstock,” said Reid. “If you have persistently infected broodstock, you will always be selling infected fish.” “This is a disease that I really don’t want anyone to bring into Ontario. And I think it’s really important that we talk about what’s happening in Quebec.”

Infectious salmon anemia virus: Reid said the industry needs to do as much as they can to prevent infected fish from coming into Ontario. “One of the issues is, every time we have a pathogenic mutant, it’s basically because there’s all these, what are called HPR0, so Highly Polymorphic Region, 0 fish…They never show clinical signs. But when you put them all together, they actually undergo mutation events and become pathogenic,” she said.

Piscine Lactococcosis: It’s a trio of three bacteria that can affect almost all fish. It’s present in the ocean and in freshwater. “It used to be really big in the 90s, it kind of went away. And now since 2020, we’ve seen this emergence of a strain all across North America that’s really quite virulent for rainbow trout,” Reid said It’s a warm water pathogen. So with climate change and changing temperatures, the disease profile risk has really changed. There might be some contributions of other subclinical diseases that sort of make fish more susceptible to this. “So I think we’ve been very lucky that this bacteria has been fairly well controlled with vaccination.” 

Bacterial kidney disease: It is one of the oldest fish diseases that affects most salmonid fish. “Rainbow trout are actually considered relatively resistant. The Pacific salmon, coho and Chinook are considered highly susceptible,” Reid said. There are no vaccines for this disease, there’s no treatment. Drugs can be used to reduce the shedding around spawning, but they don’t eliminate it. It’s passed inside the egg, so infected parents can’t produce disease-free offspring.

Whirling disease: This disease affects salmonid fish. Brown trout are the natural host and rarely show clinical signs. “This disease has been on the U.S. side of the Great Lakes for a very, very long time. We have been very lucky that we don’t have the intermediate life stage that’s required to spread this disease in Canada, or at least not a part of Canada,” said Reid. “If our winters get warmer, our summers get warmer, it’s more likely that those intermediates will become established here. And we will not get rid of this disease.”

The disease has now been detected in Alberta and despite extensive interventions, it has spread and now BC is positive. They just shut down two provincial parks to try and control it.


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Reid recommended four tools to manage uncertainties in fish health: lab testing, vaccinations, biosecurity, collaboration and information sharing.

“Vaccination is really one of the most important medical advancements in preventing disease spread,” she said. “You really need to think about biosecurity before you even have live animals on your premises. Because once you’re there, the risk of something moving and being on your farm, it’s there.”


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