goldfish lakes ontario invasive

Massive goldfish the size of footballs are cloning themselves in Ontario lakes

The ubiquitous household goldfish can be found mindlessly swimming laps around fishbowls and aquariums worldwide, but when released into wild settings like Ontario lakes, these small fish can grow to absolutely gargantuan sizes comparable to an American football.

Fisheries and Oceans Canada has long warned pet fish owners not to flush or release their aquatic companions into the wild, sharing terrifying images of the resulting massive goldfish that have established themselves as a pesky invasive species in Ontario.

In 2021, an absolute beast of a goldfish was pulled from Hamilton Harbour by a Fisheries and Oceans Canada research team, and similar finds have been noted across Ontario and British Columbia.

But that isn't even the most terrifying part. The real horror is that there's a good chance that these enormous goldfish are not former pets released into the wild, but, instead, their descendants.

Fisheries and Oceans Canada tagged and tracked these colourful behemoths and discovered that they are reproducing using crucial spawning sites for native species, displacing existing fish populations and causing other ecological damage through their consumption of plant species and waste in the water.

According to Brian Heise, an associate professor in the department of natural resource sciences at Thompson Rivers University, "the fish are hardy and reproduce quickly - releasing up to 50,000 eggs at a time, three times a summer."

That's a whole lot of eggs, but it's not the only means of reproduction for feral goldfish.

Heise told the Canadian Press in March that "female goldfish have a special process called gynogenesis in which the female will get the sperm from a different kind of minnow… to start the eggs developing, even though they're not fertilized."

In layman's terms, they're cloning themselves.

As they spread, their potential for damage to the local ecology only multiplies. Fisheries and Oceans Canada says that released goldfish and their descendants "can carry diseases and infect or harm local species and the environment, even when dead."

"The solution is simple: Don't let it loose! Never release aquarium pets or plants into sewers or waterways, such as lakes, rivers, and the ocean."

Lead photo by

Fisheries and Oceans Canada


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