I saw both kinds at the fish store. I have ovellaris's but honestly I do not see a diffrence between the two. Is there a diffrence or is it just the part of the ocean they grow up in?
Ocellaris is what you mostly find in pet stores. The main difference is mature size, perc will be a tad smaller. The Ocellaris will have a taller dorsal fin in comparison to the percs...also, coloration. Percs will have more back between the color stripings.
There are some color differences, and im sure some slight genetic differences. But because they can still cross breed and produce viable young, i would say the difference between them is slight.