Very nice pick-up. It's either a Paraneetroplus zonatum or a P. sp 'Coatzacoalcos'. The dark band running from the eye to the gill plate is the main identifier for these species ( along with the horizontal dark line running pretty much the full length of the body). It will become darker and more distinct as the fish ages. Here's a pic of a mature male P. sp 'Coatzacoalcos' in non-breeding coloration.