In my experience bettas thrive at 80F. I keep my D. margaritatus and D. erythromicron at or below 75F. I don't have experience keeping them at higher temps. I keep them below 75F because the vast majority of sources inidcated this would be best when I did my research on keeping them. I would suspect keeping them at higher temps would shorten their lifespan, but again, this is based only on research.