Does this species need to have a cool down period or is this just for breeding purposes? Can they survive in a tank that's 76-78 year round? Has anyone done this before?
For the species to thrive, they need the cool down period. If you keep them in a heated tank, you will not get any breeding and will ultimately reduce their life span.
They need the cool down period. I kept a group of male gymnos (mix of labiatus and ex-meridionalis) in with my severums and after about 9-10 months their appearance deteriorated and I lost about half of them even after I started an emergency cooling. These fish were a little over 2 years old so I believe the lack of a cool down period just wiped them out.
I 2nd abarilots recommendation,all Gymnos tend to waste away at constant warm temps and are apt to be bullied by watm water species. They do fabulous in unheated tanks, and I keep some in the pond spring thru fall in Milwaukee where water tenps drop into the high 40s with no ill effects.