There are Koi at the Evergreen Brickworks in the Don Valley. They are fat oversized Goldfish that slurp up any crumb that might fall in the water, all the while looking supremely out of place in a pond in the middle of southern Ontario. They are, presumably, escapees from aquariums, like the Painted Turtles that share the pond with them.
One would not expect exotic creatures like Koi and Painted Turtles to do well in northern climes, but Toronto has an unusually warm climate for its area, and the Don Valley especially benefits from a naturally sheltered landscape – the side of the valley are high and steep, and the temperature at the bottom is often several degrees higher than it is along the ridge. The exotic water-creatures do just fine.