Water Temps

What is the lowest water temp steelhead can survive in..? just outta curiousity

Is this a trick question?

until the water is solid?

Typically thermoregulation is studied as to tolerance for higher end temps and that gives us our warm cool and coldwater species.  I know that for lake trout erie is about as far south as you see them due to the lack of coldwater habit, so I assume that there are southern species that do not come this far north because of thier inability to handle cold temps.  I will check around.  I know that fish like Tialapa can not survive temps lower than 8 or 9 degrees C.