There are over 70 recorded different species of Angelfish found in warm water oceans around much of the world; although a few species are from fresh water. Angelfish belong to the family Pomacanthus and is named after the Latin words “pom” (cover) and “acanthus” (thorn), this refers to the spine that covers the first lower gill cover: this also helps to distinguish the Angelfish from the closely-related butterfly fish which has the similar flattened body. These brightly-colored fish live in coral reefs in tropical seas and shallow subtropical waters.
Many angelfish share a common characteristic; that the young ie juvenile are a totally different colour pattern than the adults. In fact the young ones of different species of angelfish can look more related to each other than to their parents. The Emperor Angelfish is typical example.
The Emperor Angelfish (Pomacanthus Imperator, also known as the Imperator Angel) is a reef-associated species, native to the Indian and Pacific Oceans, from the Red Sea to Hawaii and the Austral Islands.
And like mentioned, the juveline and adult Emperor Angelfish have very different coloration:
Juveniles are dark blue with electric blue and white rings. Adults have horizontal yellow and blue stripes. The eyes are enclosed by a black vertical bar with blue edging. Juveniles prefer to stay hidden under ledges or inside holes of outer lagoon patch reefs or semi-protected areas of exposed channels and reef flats. As a juvenile they sometimes set up cleaning stations in the reef where they are visited by other fish looking to rid themselves of parasites. When the juveniles are about 8-12cm they will change into their adult colouration. It takes about 24 to 30 months for an emperor angelfish to acquire its adult colouring.
As they grow older, they move to holes located at reef fronts and in surge cannels. Large adult specimens are found in areas with prolific algae growth on clear lagoon, channel, or seaward reefs. This fish typically seek shelter in caves and under ledges even as an adult. The depth range for this species is 1-100 meters and they can grow up to 40 cm in length.
The Emperor Angelfish is an egg-laying species that will scatter hundreds of eggs at a time. It forms pairs that are believed to be life long, similar to the butterfly fish behaviour. The female releases her eggs depending on tidal action, the lunar cycle and light available.
The Emperor Angelfish are not like most angelfishes which are herbivores (plant –eater), they are carnivores (meat-eater) and feeds primarily on small invertebrates like sponges and worms and other encrusting organisms, and coral heads and algae also animals like shrimp and shellfish. They can crush hard-shelled prey with their powerful, beak-like jaws.