Caution!!: Non-scientific comment to follow!
It seems intuitively correct that organisms that are made up of almost all water would favor a little temperature gap from freezing. A fish has a hard enough time fighting off everything else without fighting crystalization of it's slime layer. (Sure, I'm exaggerating, but 39 F. sounds a lot more comfortable than 34 F.) Very, very interesting the previous comment from Brian Loberger about losing his Centrarchidae but having his yellow perch survive. Perch are a true cool water fish, especially compared to bluegill and largemouth which are a little more warm water/fringe fish from an evolutionary standpoint. Could it be that perch, walleye and trout could withstand "supercooling" just a little better?
Again, no data to support this...just a little theoretical guessing.
