Great Lakes, great conquistadors | Royal Ontario Museum

With the Grass Carp approaching the Ontario border, how do we prevent them from invading?

What sparkly, iridescent glitter is worth spending millions of dollars? In this case, it’s not the gem or pink ruby, but carp grass instead.

While it may be shiny (and can reach about two meters in length), the Grass Carp is not a trophy fish. Here in Canada, we spend millions on preventing their invasion.

This may sound like a lot, but it’s just a fraction of the $7 billion fishing industry backed by the Great Lakes, threatened by an invasion of the Grass carp, a fish so large that it will outsmart the native fish and devastate. Water conditions by overfeeding.

Once they arrive, eliminating and containing them over time will end up costing much more than prevention.

So how do we keep Grass Carp away when they are so close to the border?

Fisheries and Oceans Canada (DFO) monitors the Great Lakes and their surrounding watersheds annually for the presence of grass carp. The DFO is also partnering with the Toronto and District Conservation Authority (TRCA), so they can conduct monitoring in the waters within the Toronto Regional Waterfront. The use of the DFO and TRCA monitoring protocol includes electric fishing and a variety of nets that target fish at different life stages. So far, their work has yielded promising results: Grass Carp has not been found in the Toronto area for the past seven years.

While the DFO specifically searches for grass carp, black, bigheaded, and silver carp, they still collect data on non-target species (identification, weight and length). This data shows what the aquatic community looks like, including species diversity and health. With this knowledge we can measure the impact of society in the event of an invasion.

Scientists at the University of Toronto are working to develop innovative solutions to prevent unwanted fish using non-physical barriers, such as this auditory barrier used to prevent non-native fish from entering a protected area at the Royal Botanic Gardens.

DFO is working to form partnerships with organizations like ROM to educate the public about the harm of invasive species to our native fish and their habitats. The ROM also helps the public learn about the Grass Carp and their relatives (like this silver carp from our collections), so they can help with early detection the next time they’re out on the water.

Our local ecosystems have evolved in such a way that each species serves a purpose. Small fish feed on insects and aquatic plants, which prevents population explosions. Big fish feed on smaller fish, making sure they don’t over-consume those insects and plants. Grass carp are larger fish that eat the diet of those smaller fish, feeding on wetland vegetation that once provided a critical habitat for fish, birds, amphibians, and reptiles.

Their size and novelty in our ecosystems give them the number one advantage: they don’t have predators—meaning they can keep eating and eating…and eating. Next thing you know, there is no longer food or habitat for smaller native fish, and the web is collapsing – along with human skeletons that depend on a functioning ecosystem.

Natural resources are essential to provide fresh water, round diets and stable income. But these are not just resources we are talking about. This is our home, and like the weeds we take out of our gardens, it is up to us to protect it – so that what is native can grow.

Do your part:

Report sightings of grass carp to the Invasive Species Hotline at 1-800-563-7711, or go to

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