Not only do fish have antifreeze, they also have a somewhat miraculous blood system of arteries/veins.
Even though they are cold blooded per se, they do generate small amounts of internal heat. And the structure of the veins/arteries act as a form of a living heat exchange system, which keeps that minute amount of heat concentrated in their core, where it is least likely to escape.
Counter-current exchange physiology is really something, isn’t it?