There's not really a set temperature, but I keep my fry at 78F. That's on the higher mid range of temperatures for the fish. I try to keep my fish on the warmer side as they are cold blooded.
I'm one who like to keep these fish a little cooler, their found in high land streams and take temps from 64-78oF and I aim for low 70's as i find the young are slower growning but hardier.
I keep mine at a steady 78ish it's a little warmer than normal but It helps keep them disease free... It sounds silly but I've had a lot less sick fry since I changed it from 74