
Each fish will have a termerature they are most likely to stay healthy at, this can be researched in the fish profile area under "ARTICLES", but in cases like an out break of ick you can raise the temperature to 83 for two weeks with out harm to the fish IF you do lots of water changes to keep the oxygen levels up.
As for normal conditions, fish in general age faster in warmer water. So if your fish says 75-80 degree range and has a life expectancy of 7 years, for example. At about 77 degrees they should have less problems with bacterial or fungal infections, than at 75, they will live their expected life length, and do fine, at 80 you may have even less problems with sickness, but they may only live 6 years due to faster metabolism.