The Koran Angelfish, Pomacanthus semicirculatus, is a deep-bodied, laterally compressed angelfish native to the Indo-West Pacific. Juveniles wear a dramatic blue-black pattern crossed by white and blue bands that curve into semicircles toward the rear of the body, a marking that gives the species its common name. Adults transform into a yellowish to brownish green fish with blue-speckled scales, a vivid blue eye ring, blue gill margins, blue-edged fins, and elongated dorsal and anal fin filaments. Mature specimens reach roughly 15 inches, making this one of the larger angelfishes offered to home aquarists.

In the wild this species occupies tropical coral reefs and inshore waters, with juveniles sheltering in shallow protected areas and adults ranging across coral-rich coastal reefs. Captive housing should reflect that scale of movement: a 180-gallon aquarium is the practical starting point for an adult, and larger displays produce better long-term results. A fish-only-with-live-rock layout suits the species best, built around substantial, stable rockwork with caves and crevices for shelter and grazing surfaces, balanced against generous open swimming lanes.

Because this is a large, waste-producing grazer, a well-established system is essential. Strong filtration, consistently high water quality, and brisk water movement support both the fish and the algal film it constantly picks at. Care requirements are moderate rather than beginner-level, largely because of the specialized diet and the sheer volume of water and rock the adult demands.