TJ, it has crossed my mind that those two "special" RES might have been from one of the small groups of RES that I overwintered in my aquarium over the last couple of years. None of them were ever exposed to extreme cold when they were young, this might have made them less winter hardy when they were released at a larger size. The RES that I overwintered were all 9" plus when released without ever having experienced a Nebraska winter. Could this have made them less cold tolerant? Just the nature v. nuture debate running in the back of my head.