I saw some people fishing the other day in 16 degree Fahrenheit (-9 Celsius) weather at 4:30AM. They were not ice fishing with a little hut, but standing at the base of a bridge with no shelter or campfire. People are at that bridge fishing regularly when it is cold but that was the coldest temp I have seen so far. Why is it so appealing to them?
This varies wildly depending on what species and how it was caught. Fish with really thin lips like largemouth are generally perfectly fine after being released.