"The optimal temperature is 74 - 78 F. I keep my tank at a constant 76 F. I never have to worry about my temperature fluctuating, be it winter or summer. This is in part due to the very large water to air ratio (which helps to cool it off), and more importantly, three submersible pumps (which heat the water slightly). I don't use heaters on my fry or grow-out tank, and so the temp is naturally a little lower (74 F), however, I know of people who aim for temperatures of 80 F or even 82 F with their fry tanks. This brings me to my next point.
High temperatures will increase a fish's metabolism, boost their immune response, as well as stimulate aggression. So, by raising the temperature to 80 F for a fry tank, one would speed up their metabolism, causing them to eat more and grow faster, but also require more water changes. Conversely, you could lower the temperature in your tank as a means of stemming aggression. This can be helpful if you have some really nasty fish on your hands (e.g., Melanochromis auratus, Pseudotropheus lombardoi "Kenyi"). This is due to the fact that the number one cause of aggression among Cichlids is food related. If they are not feeling a need to eat as often (because their metabolism has slowed), then they are less likely to be territorial and feisty"