Observing the placement of a fishes mouth, is very telling about how and where a certain type feeds.
For live bearers, and other fish that live in shoals and find security in numbers, the surface is home, and where they find food most of the time.
When you see a mouth on fish like the ones above, or below you know it is naturally a surface feeder.
The mouths of most cichlids suggest that the surface is not where they naturally feed (of course in a tank you can train instinct out of them)
because its dangerous place to go, unless they are too big to be easily taken (like Cichla, or Umbi's).
The most common predators of cichlids and other easy mouthfuls are birds
and not only cichlids of course