Regretably, this is not a simple question to answer. Not only does it depend on the particular type and even in some cases the particular species, but factors such as water temperature can also play a role.
Are you talking Africans or Americans? River Africans or Lake Africans, Peacocks or Mbunas? Oscars or Jewels?
You'll have to provide a little more information in regards to the specifics of what you are asking.