There are sturgeon that experience 80 degree and above water in their natural habitat for part of the year. Of course as luck would have it none of them are available as aquarium fishes. Why would you want to keep them above 80? 80 is quite warm for even most tropicals. Shovelnose sturgeon Scaphirhynchus platorynchus would survive it but best temps for them would be less than 80 mid 70's is about right but part of the year in the high 70's to low 80's would be ok. The west coast sturgeon of North America would not be good choices as they are pretty much dedicated cold water fishes. I'm not sure about the European sturgeon...