Prince Edward Island’s (PEI) oyster industry is confronting one of the most significant biological threats in its history. Since the discovery of Multinucleate Sphere Unknown (MSX) in PEI waters in July 2024, the oyster industry has been forced to respond to a disease capable of causing extreme mortality (more than 90 per cent) in eastern oysters (Crassostrea virginica). While the PEI oyster fishing and farming industry has a strong history of resilience through disease challenges, the proximity of the abnormally financially difficult Covid years, cost-inflation pressures and trade instability with the United States have created a context within which many farmers and fishers are facing a true existential challenge.

But the resilience-ethos of the PEI oyster industry is strong and on full display at the Bideford Shellfish Hatchery (BSH). Located on an estuary of Malpeque Bay, on western PEI, the BSH has become a focal point of hope for the future of the PEI oyster industry. This is because the hatchery, under the careful management of geneticist Guy Perry, has undertaken the arduous mission of using selective breeding and genomics to develop and sell MSX-resistant oyster seed to an industry searching for its next steps. In the spring of 2025, Perry and his team sold the first batch of seed from the MSX-resistance selection program. While the seed grows on Island farms, tended to with bated breath by farmers whose futures depend on their survival, the work of the crew at BSH continues in the second generation.

The arrival and impact of MSX in Prince Edward Island

MSX is caused by the protozoan parasite, Haplosporidium nelsoni. The disease does not pose any risk to human health or food safety, but it can cause near-total mortality in both wild and farmed populations. It is also a longer-term challenge in that its impacts are most pronounced in mature oysters as opposed to juveniles. While a population may seem to have avoided infection one year, the next may bring catastrophic mortality.

In Canada, it was first detected in Nova Scotia’s Bras d’Or Lake in 2002. For more than two decades, the disease remained confined to that region. Although the oyster industry in Nova Scotia was relatively small compared to that of PEI at the time, its impact was immense for that industry. In 2001, Nova Scotia harvested 438 metric tons of grown oysters and by 2006 they harvested 0.

That changed in July 2024, when MSX was detected in oysters from Bedeque Bay on Prince Edward Island. Subsequent testing identified the disease in additional areas around the province. The Canadian Food Inspection Agency (CFIA), Fisheries and Oceans Canada (DFO), and the Province of PEI increased surveillance and sampling programs significantly. Initial controls on stock, gear, vessel and infrastructure movements were extremely stringent. MSX is spread by infective parasites released by an unknown secondary host, but there’s no way to tell how many or which oysters will become infected. It was a true lockdown aimed at reducing the extraordinary risk of spreading the disease since it was unclear how it did so. Meanwhile, researchers attempted to better understand the scope of the outbreak as well as the nebulous mode of transmission.

Algae room at Bideford Shellfish Hatchery (Photo: Guy Perry)

In early 2025, the CFIA declared Prince Edward Island an area where MSX is known or highly likely to occur, meaning many of the strictest restrictions on shellfish movements within PEI were lifted, allowing farmers and fishers much more freedom to carry out their work. By September 2025, the waters of PEI, New Brunswick, Nova Scotia, Newfoundland and Labrador and Québec were also declared as such. At the same time, they were declared as the same status for dermo, another deadly and virulent oyster disease.

Although the true scale of impact from the outbreak is still coming into focus over time in PEI, a recent publication of a survey conducted by the Prince Edward Island Aquaculture Association (PEIAA) in early 2026 paints a deeply troubling picture. Some of the key findings were:

Sixty-nine per cent of farmers have reported mortality above 76 per cent
Fifty-five per cent of farmers will be hiring fewer staff in 2026
Thirty-four per cent of farmers who have financing have been in touch with their creditors about deferring payments
Twenty-one per cent of farmers do not plan to operate their farms in 2026
Of the 21 per cent who do not plan to operate in 2026, 73 per cent would change their mind upon confirmation of the availability of disease-resistant seed or new funding.
As illustrated by these numbers, the industry is now looking to survivors of MSX for hope.

The development of MSX-resistant seed

Guy Perry, a quantitative geneticist, has been the manager of BSH since November 2024, when he was specifically recruited into the position to support the development of a resistant seed program.

Within the context of extreme time sensitivity for delivering a solution to PEI farmers and fishers, Perry and his team have had to employ every means at their disposal and develop a robust program in very short order. He describes their approach as three-pronged. Of the first prong, Perry said, “The first one is the stock-based program, started in 2024, where we went out to Bedeque Bay, collected survivors and spawned them. The seed born of this spawning are out on farms right now, being assessed for survival. It’s tricky to speculate on their success yet because they are only a year old and MSX tends to most impact oysters that are two years or more, but we’re optimistic about its success based on early results.”

The second prong of their approach is utilizing genomics, “We collected dead oysters from our broodstock who had died as a result of the water we pull from the bay being MSX positive, as well as Bedeque Bay survivors and some of our stock program seed and they’ve all been sent away for genotyping. Once the results were obtained, we identified the markers most strongly associated with survival. Those which possess these markers are, presumably, MSX-resistant oysters. Once we knew those markers, we selected oysters which possessed them, and used them to spawn with the stock from our prong-1 stock program.”

The third prong is a more expanded blend of both methods, whereby they expand the scope of recruitment of oysters with these markers from different bays in PEI to bring more genetic variety into the pool of brood for subsequent spawns. He refers to this approach as hybridogenomics. He said, “we want to have several distinct hybrid groups to maintain genetic diversity to support these efforts in the long term.”

As to why he chose to employ such a sweeping approach, he said, “We just don’t have time to do things another way. The classic genomics approach would be to try a few things, then wait until the first batch grew full lifecycle, then try a few more, and wait and so on and so forth. While we might be able to achieve our research goal that way, it’s entirely possible the whole industry would have shut down in that timeframe. We had to approach this problem differently.”

Part of the broader approach

The efforts of Perry and his team at BSH are supported and complemented by a broader network of efforts by industry in PEI and beyond to stock farms with MSX-resistant seed.

One prominent North American shellfish company has brought seed from their American MSX- and dermo-positive farms to sell to PEI growers. The intention here is that these seed come from waters which have been positive for many years, and so they can be assumed to be resistant.

As well, in June 2025, Genome Canada announced a four-year, C$3.1-million projec...

Aquaculture North America

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