One of the most amazing things about keeping a juvenile Pomacanthus angelfish is to watch the transformation of the color pattern as it changes from a juvenile to an adult. The pigmentation of the various size classes are very different. In fact, for many years ichthyologists classified the juveniles of some angelfish species as distinct from the adults. One of the more common and hardy members of this genus is the semicircular angelfish or Koran angelfish (Pomacanthus semicirculatus).
Difficulty: The semicircular angelfish tends to be a fairly hardy member of the family Pomacanthidae. This is particularly true of young or subadult fish, which tend to acclimate more readily to the confines of an aquarium. The semicircular angelfish should be fed at least two or three times a day. The menu should include frozen preparations for herbivores, frozen mysid shrimp and finely chopped or grated seafood.
Physical description: The juvenile P. semicirculatus is dark blue with light blue and white semi-circles on the body. The tail has white markings with a white margin. Adults are green overall with blue spots on each scale and a blue head. The adult semicircular angelfish also has a beautiful filament on the rear edge of the dorsal fin. The transformation from juvenile to adult usually begins when the semicircular angelfish is between 3 and 6 inches. The semicircular angelfish can reach a maximum length of 14 inches. While an adult semicircular angelfish is not likely to be confused with other angelfish, juveniles are similar to those of several other species, including the sixbanded angelfish (P. sexstriatus) and the blueface angelfish (P. xanthometopon).
Range: The semicircular angelfish ranges from east Africa east to Fiji. The semicircular angelfish is found over a depth range of less than 3 to at least 130 feet near lagoon patch reefs, reef flats, reef faces and slopes. The semicircular angelfish tends to occur in coral-rich habitats where it hunts for the sponges and tunicates that make up the majority of its diet. The semicircular angelfish tends to be a solitary fish, though it is likely to be a haremic species like its close relatives.
Compatibility: The young semicircular angelfish can be a nasty neighbor in a smaller aquarium. Juveniles may not tolerate the presence of other angelfish (particularly if they have a similar color pattern) and will chase and nip at butterflyfish and rabbitfish that are smaller or similar in size. Of course, placid species, such as firefish and dartfish, are also likely targets. If you want to house P. semicirculatus with other angelfish, place the fish in a large aquarium (180 gallon aquarium or larger is optimal) and make sure the species selected are as different in coloration as possible. Also provide plenty of places to hide and select specimens that differ significantly in size (make sure the smaller fish are added before the larger ones). Do not keep two juvenile semicircular angelfish in the same aquarium. It is also risky to place adult semicircular angelfish together, unless they are housed in a very large aquarium (400 gallons or larger) and the fish are of the opposite sex (the sexes are difficult to tell apart, so it is a matter of trial and error). While the young semicircular angelfish may behave itself with sessile invertebrates, an adult may begin nipping at corals in the reef aquarium. The treelike soft corals are most likely to be ignored by large angelfish.
Aquarium conditions: The adult semicircular angelfish should be housed in a very large aquarium (at least 135 gallons, preferably more than 200 gallons). The semicircular angelfish needs plenty of good hiding places to dart into when frightened, as well as unobstructed swimming room. Keep the water parameters for the semicircular angelfish as follows: pH of 8.1 to 8.4, specific gravity of 1.019 to 1.025 and a water temperature of 74 to 82.
Care considerations: The semicircular angelfish will do well in the home aquarium if you provide it with enough space and a varied diet (that includes some plant material). As with any potential aggressive marine fish, the more space available, the less likely aggression with be a real problem.
Breeding: The semicircular angelfish is not likely to spawn in the home aquarium.