Theo,
According to this source it's lethal limit is 95 F. I'm skeptical. Sounds pretty high to me for smallmouth.
http://aquanic.org/publicat/state/il-in/as-508.htm Interestingly I do know a few years ago the IN Fisherman magazine had an article that stated the smallmouth being a cool water fish may be a misnomer. The theory is that the reason one finds them in deeper cooler waters than largemouth is they may not be able to compete with largemouth in the shallower warmer waters and are pushed deeper. I swear I remember reading an article in one of the first Pond Boss magazines that quotes a grower in the south saying they did just fine in 80 plus degree water.
Believe it or not they are calling the northern largemouth bass now a cool water fish now in aquaculture circles.
I had a grower tell me his smallmouth are the first to go off feed in the fall and the last to start up again. Odd for a fish that is supposed to want cooler water.
I rarely catch smallmouth bass icefishing in my pond but routinely catch largemouths.
