Emporer Angelfish (Pomacanthus imperator) primarily inhabits the shallow reefs, and can be found in the Lagoon at Lady Elliot, the southern most Great Barrier Reef Island.. They closely resemble the Butterflyfish, but the main difference when identifying them, is that Angelfish have a spur situated under the gill plates. Angelfish have a small mouth and laterally compressed body. Colouring on the Angelfish is vibrant, deep and showy. The pattern and colour of the juveniles are different to the adult stage. Juveniles have electric blue and white rings on a dark blue background whilst the adults have blue and yellow stripes with a black mask around the eyes. An Emporer Angelfish aquires it's adult colouring over four years. They grow to 40cm in length Female harems appear to be a method of grouping. Females outnumber males.