The coloring appears to be that of a flowerhorn, but the lack of a giant hump oni ts head at 12inches makes me think otherwise. Perhaps it is a hybrid with somethign else? A Jack Dempsey or something similar?
Either way, its most likely got a very nasty disposition, and would prolly scare the hell out of your smaller fish, if it doesnt eat them. It would be a risky move for sure.