I've studied RES as much as possible, and have quite a bit of hands-on experience, and my working theory is that a redear sunfish can live quite a ways north, as long as there is good oxygen content in the entire water column. Well-oxygenated water near the bottom of a frozen pond or lake is near 39 degrees, and this seems to be within the tolerance of RES, as long as there is not ice for very extensive periods of time. RES that live under the ice where there is poor water quality, will be forced from the warmer depths into better oxygenated upper tier waters because of decaying organic matter, but then encounter colder and colder conditions as they near the ice/water interface. This increases the stress levels on an already stressed animal.
Holding a redear sunfish is like running with scissors.
