The Flagfin Angelfish (Apolemichthys trimaculatus), also known as the Threespot Angelfish, carries a bright yellow to golden body accented by blue-edged scales and vivid blue lips. Dark markings appear near the forehead, mid-body, and dorsal fin base, though the number of visible spots varies from individual to individual. The striped black-and-white anal fin and elongated dorsal filaments give the species its common name. Adults reach roughly 10 inches. The natural range spans the Indo-Pacific, from East Africa through Southeast Asia and Micronesia, north to Japan, south to Australia, and east to Samoa, with populations also reported around the Maldives, Sri Lanka, and the Red Sea.

In the wild this angelfish occupies coral-rich reef slopes, drop-offs, lagoons, and seaward reefs from shallow water down to about 60 meters. Juveniles remain deeper and more secretive, while adults range more widely and are encountered alone, in mated pairs, or in loose groups. A mature, well-established aquarium of at least 125 gallons suits an adult, and larger systems serve the species better given its size and patrolling habits. Build the aquascape around abundant live rock arranged into caves, overhangs, and crevices, since new arrivals are shy and benefit from an established layer of algae and biofilm to graze. Leave generous open water for swimming, and pair the rockwork with strong filtration and good flow. This should be the only large angelfish in the system unless the tank exceeds 200 gallons, and it is best introduced after more passive tankmates have settled in.