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A tiny goldfish might look cute in a fishbowl on your shelf, but if released into the wild it can grow to a terrifying size and become a menace to the ecosystem. They eat pretty much anything and everything, root up plants causing the water to become cloudy and dark, and reproduce and grow so quickly that almost no predators can stop them.
“None of that is ecologically or aesthetically desirable,” says Hugh MacIssac, who studies aquatic invasive species at the University of Windsor.
Feral goldfish have been invading much of North America, including the Great Lakes, for decades and recently their numbers seem to be rising rapidly. The reason for the uptick is not clear, but it could be because invasive carp are being better controlled, and the goldfish are taking their place. New designs for stormwater ponds, where people often dump unwanted fish, that allow the ponds to overflow into nearby waterways could also be boosting the numbers.
While goldfish may seem small and vulnerable, they are actually very good invaders. They are hardy and adaptable, able to survive and thrive under a wide range of temperature and oxygen conditions that many native species can’t handle.
Feral goldfish are menacing Great Lakes: We’re going to need a bigger bowl | Bridge Michigan
Tracking escaped goldfish in Hamilton Harbour could help control the invasive species.
