I caught 3 RES in Raystown Lake in central PA last year. The first time I ever caught them in that lake. Not sure how they got there but that same lake supports lake trout and Atlantic salmon... So they can handle the cold. Raystown Lake is also 8,300 acre and over 180 feet deep in spots near the dam so it definitely doesn't have quick temperature changes. I wouldn't count on RES surving in an 8 foot deep 1/2 pond in the same area...
