Aquarium Fish Poised to Invade Lakes

People dumping their pet fish into local waterways could introduce yet another exotic species into the Great Lakes watershed.

About seven percent of Montreal residents who have aquariums admit to releasing live fish into the environment.

Some turn their fish loose after becoming bored of their pets, while others free fish that have gotten too big or aggressive. Altogether, Montrealers release an estimated ten thousand fish from their aquariums into Great Lakes and St Lawrence Seaway waters each year.

Most of these fish are tropical species that can't survive year round in the chilly Canadian outdoors. Among the five aquarium species that do tolerate cold, two popular pets have already established themselves in the region's waters: goldfish and koi carp. Two others, weatherfish and hogchoker, are too rare among aquarium enthusiasts to be released in numbers sufficient for establishing wild populations.

But one other species that withstands cold could likely move into local wetlands, according to scientists at McGill University. They estimate that 117 of the cold-tolerant white cloud mountain minnows (Tanichthys albonubes) are let loose each year. The quantity of pet minnows released is enough of what scientists term "propagule pressure" for the species to breed in the wild and become a permanent invasive inhabitant of the region.

Cold winters protect the St Lawrence region from most of the 250 aquarium fish species sold by pet stores in Montreal. Warmer parts of North America, though, are much more vulnerable to invading aquarium cast offs. Based on the findings of their Montreal study, McGill University researchers estimate that Vancouver's milder climate renders its lakes and ponds vulnerable to supporting nine species of commonly discarded aquarium fish.

At even greater risk of being overcome by exotic fish is Florida's tepid Lake Okeechobee. The lake is susceptible to becoming populated by 55 species of aquarium fish released by Miami residents.


Erin Gertzen, Oriana Familiar and Brian Leung. 2008. Quantifying invasion pathways: fish introductions from the aquarium trade. Canadian Journal of Fisheries and Aquatic Sciences. 65(7): 1265-1273.

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