The Koran Angelfish or Semicircle Angelfish, Pomacanthus semicirculatus , is said to be the easiest of the Pomacanthus angels. To a certain extent that is true. They have the same needs as other Pomacanthus , but they are just not a “touchy” making them an easier angelfish to keep. As they move into adulthood they are smart and become very personable.
Like many angelfish, the Semicirculatus Angelfish changes color when it enters adulthood. Watching an adult swim around, one may wonder where the name Semicircle Angelfish even came from. The juvenile is colored dark blue with lighter blue edging and white semicircular markings. The name describes one of the juvenile’s semicircle shaped white stripes, the one that is near the back of the tail fin. The other stripes are curved a little, but the last one has a sort of “C” shape, it can be an “O” shape in some individuals. The “C” shaped stripe can be helpful to identify the correct species when purchasing. Other common names it is known by that are describe its juvenile form are Semicircle Angelfish, Semicirculatus, Half-Circle Angelfish, and Halfcircled Angelfish.The Koran Angelfish is of medium difficulty. It is one the best "first" fish for those new to keeping large angelfish. A couple of other good first large angelfish include the Lamarck's Angelfish Genicanthus lamarck and the Indian Yellow-Tail Angelfish Apolemichthys xanthurus. The maximum size of the Koran Angelfish is 15” (38 cm). The size of these angels when they start to change color is from 3 to 6” (8 - 16 cm). As small juveniles, they make good community fish, but as young adults they start becoming contentious towards other angelfish and similarly shaped fish added later on.
A single specimen can be kept in a 135 gallon (522 l) tank. Eventually it will need a very large tank to reach its full adult size and bright coloration, between 225 to 275 gallons (852 to 1041 l). When the correct tank parameters are met, these angels can acclimate and are moderately hardy as adults. The larger sized tank will encourage proper adult coloration, reduce stress and illness, and a longer lifespan.The Semicircle Angelfish are not considered reef safe. For a fish only tank, the Koran Angel has attitude even as a juvenile, so they need to be added to the tank last. They “don’t play nice with others,” bullying smaller peaceful fish like blennies, clownfish, etc. They will also attack other Angelfish. Adding them to a tank that is at least 6 months old is advisable so there is plenty of live rock to graze on. Shape the rocks into cave type formations to provide several hiding areas, and choose a juvenile between 2” to 5” for best results.