Hogchoker

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 not 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 inhabitant of the region invasive.source