In this photo you can see a couple of Pennant Coralfish (heniochus acuminatus). This is a 25 cm tropical fish that can be found in the warm waters of many oceans in the world.
When they are small they usually live alone and may sometimes pick on parasites on the epidermis of other fish, but when they grow up they tend to live in couples and feed on plants.
As you can imagine this is a harmless species.