Cuvier in Cuvier and Valenciennes, 1831
The Moorish idol, Zanclus cornutus ("crowned scythe"), is a small marine fish species, the sole extant representative of the family Zanclidae (from the Greek ζαγκίος, zagkios, "oblique") in order Perciform. A common inhabitant of tropical to subtropical reefs and lagoons, the Moorish idol is notable for its wide distribution throughout the Indo-Pacific. A number of butterflyfishes (genus Heniochus) closely resemble the Moorish idol. It is closely related to, if not a direct descendant of, the extinct Eozanclus brevirhostris, from the Middle Eocene of Monte Bolca.
The Moorish idol got its name from the Moors of Africa, who purportedly believed the fish to be a bringer of happiness. Moorish idols are also popular aquarium fish, but despite their popularity, they are notorious for short aquarium lifespans and sensitivity.
Physical description 
With distinctively compressed and disk-like bodies, Moorish idols stand out in contrasting bands of black, white and yellow, which makes them attractive to aquarium keepers. The fish have relatively small fins, except for the dorsal fin whose six or seven spines are dramatically elongated to form a trailing, sickle-shaped crest called the philomantis extension. Moorish idols have small terminal mouths at the end of long, tubular snouts; many long bristle-like teeth line the mouth. The Moorish idol differs from butterflyfish in having a prominent black, triangular-shaped anal fin.
The eyes are set high on the fish's deeply keeled bodies; in adults, perceptible bumps are located above each. The anal fin may have two or three spines. Moorish idols reach a maximum length of 23 centimeters (9.1 in). The sickle-like dorsal spines shorten with age.
Range and habitat 
Generally denizens of shallow waters, moorish idols prefer flat reefs. The fish may be found at depths from 3 to 180 metres (9.8 to 590 ft), in both murky and clear conditions. Their range includes East Africa, the Indian Ocean and the Ducie Islands; Hawaii, southern Japan and all of Micronesia; they are also found from the southern Gulf of California south to Peru.
Sponges, coral polyps, tunicates and other benthic invertebrates constitute the bulk of the Moorish idol's diet in the wild. Captive Moorish idols typically are very picky eaters. They will either eat nothing (common) and perish or eat everything (uncommon).
Often seen alone, Moorish idols also form pairs or occasionally small schools, especially as juveniles. They are diurnal fish, sticking to the bottom of the reef at night, adopting a drab coloration. Like butterfly fish, they mate for life. Adult males display aggression toward one another.
Moorish idols are pelagic spawners; that is, they release eggs and sperm in the water column, leaving fertilized eggs to drift away with the currents. The range of these fish may be explained by the unusually long larval stage. The fish reach a length of 7.5 centimeters (3.0 in) before becoming free-swimming juveniles.
In aquaria 
Some aquarists prefer to keep substitute species that look very similar to the Moorish idol. These substitutes are all butterflyfishes of the genus Heniochus, and include the pennant coralfish, H. acuminatus; threeband pennantfish, H. chrysostomus; and the false moorish idol, H. diphreutes.
Cultural references 
- In the 2003 Pixar film Finding Nemo, a Moorish idol named Gill (voiced by Willem Dafoe) was one of Nemo's tank inhabitants. Gill was depicted having a very strong desire for freedom outside of the aquarium and was constantly scheming in order to achieve this, possibly referencing real-life Moorish' idols difficulties with captivity.
- Moorish idols have long been among the most iconic of coral reef fauna. They have graced all types of underwater-themed products, such as shower curtains, blankets, towels, and wallpaper.