they have them here in northern montana and in canada, so that should tell you they can handle extremely cold water, and they also live throughout the rest of the US so they can handle just about any water condition. I have seen them kept with koi alot. I saw one in an indoor pond with koi that was around 36" and probably wieghed around 30 lbs or so. Don't under estimate this fish the world record is like 58 lbs, but don't qoute me on that. I know it's over 50 anyway. Good luck, and if you get tired of them, i know a good southern catfish dish i can share! jk