eurasian ruffe ontario

Rapid-breeding invasive fish species spotted in Ontario and you should kill them on sight

An invasive fish species that is capable of massive eco-destruction has been spotted in Ontario, and aside from reporting sightings of the fish, experts are recommending anglers to kill them on sight. 

The Eurasian Ruffe (Gymnocephalus cernua) is a small member of the perch family and is native to northern Europe and Asia, with the potential to wreak havoc across lakes in and around Ontario. 

According to Ontario's Invading Species Awareness Program, it is suspected that the species was transported to North America in the ballast water of vessels arriving from Europe in the mid-1980s. 

In Ontario specifically, Eurasian Ruffe have been found in the Kaministiquia River near Thunder Bay, as well as Lake Erie, Lake Superior, and just recently, outside of Sault Ste. Marie. 

On the biodiversity tracking website, iNaturalist, Ontario residents have submitted several sightings of the species around Sault Ste. Marie and Thunder Bay. 

The invasive species is capable of adapting to a wide range of environmental conditions, including fresh or brackish water with either low or high nutrients, as well as a range of depths and temperatures. 

Ruffe typically consume a variety of foods and have very few predators thanks to the the presence of hard dorsal spines on their fins, making them difficult for other organisms to eat. 

The species resembles juvenile Walleye, Yellow Perch, and Trout Perch, but they can be distinguished by their perch-like bodies — which are typically less than 20 centimetres long — glassy eyes, down-turned mouth, and the olive-brown colour on their backs. 

Ruffe also lack the dark vertical stripes found on the native Yellow Perch, and they have no scales on their heads. 

The species can have devastating impacts on Ontario's ecosystems and lakes by directly competing with native sportfish populations for food and habitat. 

Thanks to their rapid reproduction and growth rates, Ruffe can quickly become the most dominant fish in local areas, which puts immense pressure on native species and contributes to their decline. 

A single female has the potential to lay anywhere from 130,000 to 200,000 eggs annually, with the species' primary spawning season occurring from the middle of April through June. 

According to Ontario's Invading Species Awareness Program, the fish have the potential to spread to each of the Great Lakes and many inland waters. 

If caught, anglers are asked to kill the fish, and spottings can be reported to the Invading Species Hotline or on websites like iNaturalist, which helps local scientists and professionals keep track of the province's biodiversity.

Lead photo by

guentermanaus/Shutterstock


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