Moorish idol
The Moorish idol ("Zanclus cornutus") is a marine fish species, the sole extant representative of the family Zanclidae (from the Greek ζαγκίος, "zagkios", "oblique") in order Acanthuriformes. 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 brevirostris", 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 a coveted aquarium fish but, despite their abundance and wide array of habitats, they are notoriously finicky and hard to adjust to captivity. Their omnivorous diet can be extremely difficult to replicate in aquaria, as the vegetation which they live on is normally exterminated and they have a habit of eating corals and sponges. 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 anal fin. The eyes are set high on the fish's deeply keeled body; in adults, perceptible bumps are located above each. The anal fin may have two or three spines. Moorish idols reach a maximum length of . The sickle-like dorsal spines shorten with  age. Distribution and habitat. Generally denizens of shallow waters, Moorish idols prefer flat reefs. This fish may be found at depths from , in both murky and clear conditions. Their range includes: East Africa, the Indian Ocean, Persian Gulf, the Ducie Islands, Hawaii, southern Japan and all of Micronesia; they are also found from the southern Gulf of California south to Peru. Feeding. Sponges, coral polyps, tunicates and other benthic invertebrates constitute the bulk of the Moorish idol's diet. Behavior. 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. Reproduction. 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 before becoming free-swimming juveniles. In the aquarium. Moorish idols are notoriously difficult to maintain in captivity. They require large tanks, often exceeding , are voracious eaters, and can  become destructive. 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". Moorish idols typically are very picky eaters. They will either eat nothing (common) and perish or eat everything (uncommon).