Okay so I have a deep outside pond that has two sections with a waterfall and is about 20-25 gallons of water. I want to get a cold water fish that is okay with water getting up to at least 80 as outside in the summer the water can really heat up but since it's in the shade it shouldn't get too hot. I normally plant new plants into the pond every year as the old ones freeze out.
So basically I want fish that are small and can stay small but are hardy enough to survive life in an outside pond so not goldfish or koi (even though I LOVE koi, or carp. Want them to be hardy that will live for years and maybe make some babies while they are at it.
Also since I live in a state with winter they have to be able to transition to life outside to living inside in a 20 gallon fish tank. I was thinking of some sort of minnow but not sure what to get, obviously not a tropical fish of any sort.