sea lamprey ontario

Parasitic 'vampire fish' populations about to explode in Ontario lakes and rivers

One of the most horrifying invasive species in Ontario is about to begin its annual breeding frenzy: the parasitic, vampire-like sea lamprey.

These slippery serpentine creatures native to northern oceans have been wreaking havoc on the Great Lakes for almost 200 years, likely introduced through ships travelling the Erie Canal.

The jawless eel-like species has established itself well in this period by preying on local fish in an absolutely revolting fashion.

Sea lamprey attach themselves to prey with suction-cup-like mouthparts lined with horrifying concentric rings of teeth that act as sawblades to help them gradually drain victims of blood.

Its victims' blood stays flowing through the slow and painful ordeal with the help of an anticoagulant, hemolytic and cytolytic chemical secreted in lamprey saliva called lamphredin.

While they've been present in Toronto waters since back when the city was known as the Town of York, lamprey have been able to penetrate much further inland since the early 20th century, when the Welland Canal gave all aquatic species unobstructed access to the upper Great Lakes.

Established sea lamprey populations typically explode in the spring and early summer months during their breeding season.

Sightings of sea lamprey in Ontario lakes and waterways can be reported using social network biodiversity app, iNaturalist, which shows spikes in encounters from April to June that offer some insight into the seasonal spread of sea lamprey.

Every year, the Toronto and Region Conservation Foundation (TRCA) works to curtail the spread of this invasive species, rounding them up in the hundreds and dispatching them.

The Rouge River at the east edge of Toronto is another hotspot for sea lamprey. The Great Lakes Fishery Commission just concluded a treatment of the river this spring, killing off thousands of lamprey larvae.

Still, despite boatloads full of these predators being removed from the province annually and many more killed off as larvae, local anglers know all too well the damage being caused by these invaders.

In 2022, angler Dustin Pearl caught a massive pike while fishing from the dock wall of a downtown Toronto park. Many commenters suggested that the large fish had endured multiple lamprey encounters based on several circular scars visible.

So, next time you decide you want to take a swim in the lake to cool off on a hot day, think about things like lampreys — but also predatory water fleas, aquatic zombie plants, self-replicating crayfish and other invasive freshwater horrors you may not have known about.

Lead photo by

Theresa Grace/Shutterstock

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