Koran Angelfish (Semicircle)

Geographic Origin and Biotope: A very widespread species in the Indo-Pacific: from the Red Sea and East Africa to Fiji, Samoa, and Japan. It is an iconic inhabitant of vegetation-rich coastal coral reefs, deep lagoons with growing corals, and marine wrecks, from 1 to 40 meters in depth.

Taxonomy and Morphology: Known as the Koran Angelfish or Semicircle Angelfish. It is a large pomacanthid, reaching up to 35-40 cm (14-16 inches) in captivity (with the correct tank). Possesses the classic massive, elliptical, strongly compressed body and the lethal backward-facing "spine" on the preopercular cheek.

Social Behavior: Has a very strong and expansive personality, is highly interactive with its owner but brutally aggressive with fish that share its habitus (colors, shapes). Adults patrol large coastal territories alone to defend their food resources. Juveniles are shy and live holed up in shallow waters.

Coloration and Sexual Dimorphism: Like others of its genus, it drastically changes livery. Juveniles (up to 10 cm) are spectacular: blue-black with "semicircle" arched white and light blue stripes (hence the name). Adults turn a crazy yellowish-green sprinkled with endless neon blue dots, with fin edges outlined in brilliant blue. No dimorphism.

Aquarium Setup: Needs no less than 800 liters (210 gallons). Smaller tanks permanently halt its color change to the adult one (a sign of induced stunting and inescapable stress). Enormous rockworks, deep caves, and vast frontal space to cut through the water. Oversized filtration is indispensable to stem the heavy organic load.

Diet and Feeding: Omnivore predominantly grazing on sessile invertebrates. On the reef, it devours sponges, tunicates, and algae. In the aquarium hobby, it is perhaps the least fussy eater of the large angels: voraciously eats granular feeds, spirulina-enriched flakes, Nori, open clams, and mysis. Needs 50% greens to avoid intestinal blockages.

Water Quality: Very resistant to non-ideal chemical conditions (which is why it is often the first large angelfish tried by hobbyists). Tropical marine temperature: 24-28 °C (75-82 °F). pH: 8.1-8.4, specific gravity: 1.020-1.025. Prefers a high Redox potential and plenty of surface current.

Compatibility and Tankmates: Reef demolisher. Will tear to pieces soft corals, brain corals (LPS), zoanthids, and Tridacna clams. Should be kept in large FOWLR tanks with equally bold and large tankmates (Moray eels, Triggerfish, groupers, large tangs). Intolerant of conspecific angelfish or similarly colored juveniles.

Aquarium Reproduction: Never succeeded. Evening pelagic release of tiny, floating eggs. The larval stages in the sea feed for months on microscopic phytoplankton that cannot be reproduced in commercial quantities. Store availability relies entirely on wild collection from immense juvenile stocks in the Pacific.

Risks and Diseases: Extremely sensitive to high doses of copper, which compromises the intestinal microbiome crucial for sponge digestion. Sensitive to HLLE (Head and Lateral Line Erosion) if not fed with fresh vitamins and Nori. Can scratch itself severely on sharp edges if forced into cramped tanks.