Pomacanthus imperator

Lore & Background

The emperor angelfish was first formally described in 1787 as Chaetodon imperator by German physician and naturalist Marcus Elieser Bloch, with the type locality given as Japan. Some authorities place it in the subgenus Acanthochaetodon. The specific name imperator means 'emperor' and reflects the Dutch name Keyser van Iapan meaning 'Emperor of Japan' coined by publisher Louis Renard in 1719, possibly reflecting its majestic appearance.

Juveniles have a dark blue body with concentric curving lines of pale blue and white, while adults are striped with blue and yellow horizontal stripes, a light blue face with a dark blue mask over the eyes, and a yellow caudal fin. A blackish band above the pectoral fins has a bright blue front margin and a thin yellow rear margin. Pacific Ocean adults sport a filament trailing from the rear of the dorsal fin, absent in Indian Ocean populations.

The species is found at depths between 1 and 100 metres, with adults in areas of rich coral growth on clear lagoon, channel, or seaward reefs, often under ledges and within caves. Its diet comprises sponges, other encrusting organisms, and tunicates. They form pairs, and juveniles and adults may act as cleaner fish, cleaning ectoparasites off larger fishes. When frightened, they can produce a knocking sound.

Reader's Guide

The emperor angelfish is notable for its widespread Indo-Pacific distribution, occurring from the Red Sea and East African coast to the Tuamotu Islands, Line Islands, southern Japan, Great Barrier Reef, New Caledonia, and the Austral Islands. Vagrants have been recorded from Hawaii, and since 2009 it has been recorded as a Lessepsian migrant to the eastern Mediterranean basin, where it now occurs in low numbers at several localities. It has also been recorded off the coast of Florida and Puerto Rico.

The species is generally associated with stable populations and faces no major threats of extinction. It is common in the aquarium trade, and its unique, brilliant pattern of coloration makes it a favorite of photographers, artists, and aquarists. The marked difference between juvenile and adult coloration, along with the presence or absence of a dorsal filament depending on ocean population, adds to its biological interest. Its ability to act as a cleaner fish and produce a knocking sound when frightened are additional distinctive traits.

Did You Know?

• The emperor angelfish was first described in 1787 as Chaetodon imperator by Marcus Elieser Bloch.
• Adults of the Pacific Ocean population have a filament trailing from the rear of the dorsal fin, which is absent in the Indian Ocean population.
• When frightened, these fish can produce a knocking sound.