The emperor angelfish, Pomacanthus imperator, is a member of the Pomacanthidae family. The Pomacanthidae family includes all marine angelfish. There are seven listed genera and 86 species collectively called angelfish. None of these species are freshwater fish. Angelfish populate shallow-water reef formations in tropical ocean regions. The emperor is indigenous to the Indian and Pacific oceans. Its habitat ranges from the Red Sea to the coast of Hawaii and from southern Japan to the Great Barrier Reef.

The Emperor gets its name from its majestic color palette consisting of electric blue, royal blue and bright yellow. The coloration of this species is clearly different between adults and juveniles. When young, this species has a deep blue color on the body and tail fin. Contrasting dramatically against the dark body are concentric circles of black and white rings that expand much like ripples in still water when disturbed by a falling object. These circles start in the tail region and work their way to the head of the fish. At approximately four years of age, the fish will undergo a morphological color change as part of its transition to adulthood. Adults have blue and yellow horizontal stripes along their body, a black mask, bordered with blue around the eyes, and tail fins that are yellow instead of dark blue. Captive-bred juveniles are generally not as vividly colored as their native counterparts. This may be due to a nutritional deficiency in captivity that has yet to be determined.

These are one of the most expensive saltwater species. You can expect to pay anywhere from $80 to over $300 for one of these fish, depending on their size and level of maturity. These fish are also traded as Imperator (commander of the Roman legions) or Imperial Angelfish.

This species is not recommended for the hobby aquarist. They are intolerant of anything but pristine water conditions. They grow to an adult length of 15 inches. They require a minimum tank size of 100 gallons. They are also prone to parasite infestation. If you have a quarantine tank it is advisable to isolate them for a minimum of two weeks before introducing them to your other fish. If you buy one from a local retailer, they may agree to quarantine it as part of the purchase agreement.

These are moderately aggressive animals. They tend to intimidate smaller fish and may well eat them. They should only be housed with larger species of a similar nature. Emperor fish are extremely territorial with members of their own species in the far reaches of captivity. You should not try to add more than one to your aquarium.

Although native to tropical reefs, this species is not a suitable candidate for a marine reef aquarium. These fish will become very large omnivores. They will readily devour the smallest crustaceans in your reef tank. And they will see both your collection of soft and stony corals as a delicacy to savor.

Remember that this species is known to have an as yet unidentified nutritional deficiency when bred in captivity. They should be fed a diverse diet that mimics their dietary habits in the wild as closely as possible. They will eat frozen seafood, vitamin-enriched brine shrimp, and seaweed. Your diet should be supplemented with fresh, chopped seafood from your grocery store on a regular basis. Shrimp, molluscs, squid and octopus are recommended entrees. You can buy marine foods specially developed for angelfish. They will include a percentage of sponge cake in the ingredients. The sponge is a primary source of nutrients for these fish in the wild. It is strongly recommended that you thoroughly research the dietary requirements of this species before deciding to go to such a large expense.