Pomacanthus imperator ranks among the most recognizable large angelfish on Indo-Pacific reefs, with a range extending from the Red Sea and East Africa to Hawaii and the Tuamotu Archipelago, and from southern Japan south to the Great Barrier Reef and New Caledonia. Adults grow to roughly 15 inches and carry a deep blue body ruled by bright yellow horizontal stripes, a black eye mask outlined in blue, and a yellow to orange caudal fin. Juveniles bear no resemblance to the adult form: dark navy to black, marked with concentric white and electric-blue rings, a difference so pronounced that the two phases were once treated as separate species. The color change begins around 4 to 6 inches and may take many months to a couple of years to finish.

Adult housing should begin at 220 gallons, approximately seven feet long by roughly two and a third feet wide and two feet tall, since this fish patrols the entire water column rather than holding to one corner. Build the rockwork into overhangs, caves, and ledges that echo the reef structure it shelters in at home, where it occupies everything from shallow lagoons to depths near 100 feet, and leave a generous open lane for cruising. A mature, fully established system matters here, because part of its natural grazing involves picking algae and microfauna from seasoned live rock. Strong filtration and stable water chemistry are non-negotiable given the waste output of a fish this size, and a secure lid suits an animal that swims this actively.