Peter is entering a new phase - Quizmaster!
FWIW the hottest I have seen a fish here in OZ was a Coral trout that I had
in my oven over the weekend at around 350 F.
Perhaps you mean Freshwater and living/functioning when you posed the
"found" question Peter ?
There have been reports of Spangled Grunters (and Mogurndas too I think)
coming out of almost boiling bores but they were "cooked" and the
suggestion was that they were sucked in from nearby streams by the boring
process.
>From memory Dalhousie Springs Hardy heads must come into reckoning for
their habit of rushing in and out of extremely hot areas of the springs
complex.
The details of the exact temperatures escapes me.
Bruce Hansen