There are fish species that can tolerate low temperatures, Koi can manage to overwinter in below freezing temperatures outside.  Tout and Salmon are other species that prefer colder temperatures.  Most other fish species will not survive outside through a freeze, so be sure to check the temperature range of the fish you intend to grow.

Both plants and bacteria cannot survive temperatures around or below freezing (0C – 32F), so growing outdoors through the winter isn’t feasible without a greenhouse to keep extreme temperatures regulated.  Without bacteria, you can expect ammonia levels to build up in your tanks, eventually killing your fish.