High quality water, when covered with ice, but not much snow can maintain oxygen throughout the water column during the winter, thus giving (as Theo said) a 39 degree refuge for the winter. Maybe even a little food to boot. We see this repeatedly in central Nebraska borrow pits where we have excellent overwintering capabilities of RES
In water bodies where redears are forced closer and closer to freezing level waters RES begin to stress, and often die when exposed for a period of time to this cooler water.
Ask Dr. Willis sometime what he saw at my farm. It was a February day, and we were seining RES out of a pond that had been ice covered for months and they were absolutely gorgeous. But when they went into a horse tank with 33 degree water, they perished right before our eyes, even as the bluegill swam about unaffected.
Colder water stress compounded by duration equals dead redears.
...by the way, I'm convinced that you made a smart move acquiring the RES from a more northern broodstock.
