The adult Emperor Angel (Pomacanthus imperator) has a yellow body crossed with diagonal blue lines. The tail is yellow and a small area around the mouth is white. A dark blue colored area extends along the bottom of the fish and up to the back of the gill cover. A dark blue and black bar covers the eye. Juvenile Emperor Angelfish are dark blue with concentric white lines that are curved and form a circle towards the rear of the fish. Juveniles are very similar to the Koran Angel (P. semicirculatus) but the white bars in the juvenile Koran Angel do not form a complete circle. Numerous other juvenile angelfish also have a black, blue and white striped pattern. Although the Emperor Angelfish can reach 15" in the wild they usually only reach about 12" in captivity.
The larger angelfish available in the aquarium trade include those from the genera Apolemichthys, Chaetodontoplus, Holacanthus, Pomacanthus, and Pygoplites. Of these, Apolemichthys and Chaetodontoplus are generally the smallest and are sometimes considered "pygmy angels" compared to the much larger Holacanthus and Pomacanthus angels. The Regal Angelfish, Pygoplites diacanthus is the only fish in the Pygoplites genus.
Juveniles and adults among these angels usually have very different appearances and, in the wild, usually live in harems with dominant males controlling a group of females.The color change in angels can be triggered by size, age or a change in social structure. Angels should not be kept with other large angels in the home aquarium to avoid territorial conflicts. Occasionally, two angels may tolerate one another in a very large aquarium if they have very different coloration and appearance, but is not typically recommended.
Suitable tankmates for most large marine angels would be larger community fish like tangs, triggers, groupers, some damsels, butterflies and similar fish. More shy and passive angels can be kept with smaller, more docile tankmates. Be sure to take the adult size of the angelfish into consideration when choosing an angel for an aquarium as many can grow very large (albeit slowly) and need tankmates and an environment that can accommodate them. All angels have cheekspines at the edge of their gill cover and in the dorsal fin. Use caution when handling and avoid using a net that they may become stuck or tangled in.
The diet of large angels generally consists of meaty foods, algae, and marine sponge. Many frozen angel formulas and flakes may have extra sponge meal, and live sponges can be purchased to supplement their diet. These angels are not reef safe and have been known to nip at or eat some corals, sponges, and clam mantles. Some leather corals and anemones may be safe with larger angelfish but is not generally recommended.