Moorish idol

The Moorish idol (Zanclus cornutus) is a species of marine ray-finned fish belonging to the family Zanclidae. It is the only member of the monospecific genus Zanclus and the only extant species within the Zanclidae. This species is found on reefs in the Indo-Pacific region.

Taxonomy
The Moorish idol was first formally described as Chaetodon cornutus in 1758 by Carl Linnaeus in the 10th edition of the Systema Naturae with "Indian Seas" given as its type locality. In 1831 Georges Cuvier classified it in the new monospecific genus Zanclus. In 1876 Pieter Bleeker proposed the monotypic family Zanclidae. The Zanclidae is classified within the suborder Acanthuroidei of the order Acanthuriformes. Some authors classify the Moorish idols in the surgeonfish family Acanthuridae but the absence of spines on the caudal peduncle is a clear difference between this species and the surgeonfishes. However, Eozanclus brevirostris, an extinct species from the Eocene that is a close relative of the Moorish idol seems to be intermediate between the surgeonfishes and the Moorish idol.

Etymology
Moorish idol's unusual name was apparently given to it because, in some areas of south-east Asia, fishermen have respect for these fishes, releasing them when caught and honouring them with a bow after their release. In this case, Moor being erroneously used as it usually refers to Amazigh people from Morocco where this fish does not occur in the wild. The genus name Zanclus is derived from the Ancient Greek word zanklon, meaning "sickle", and is an allusion to the long curved dorsal fin. The specific name, cornutus, means "horned", and refers to the small bony protuberances over the eyes.

Description
The Moorish idol's body is highly compressed and disc-like in shape with a tube-like snout and small bony protuberances above the eyes in adults. The mouth is small and has many long, bristle like teeth. There are no spines or serrations on the preoperculum or caudal peduncle. The dorsal fin is supported by 6 or 7 spines, which are elongated into a long filament which resembles a whip, and between 39 and 45 soft rays. The anal fin contains 3 spines and between 31 and 37 soft rays. The maximum published total length is 23 cm, although 21 cm is more typical. They have a white background colour, with two wide black vertical bands on the body with a yellow patch on the posterior end of the body and a yellow saddle on the snout. The caudal fin is black with a white margin.

Distribution and habitat
The Moorish idol has a wide range in the Indian and Pacific Oceans. They are found from the eastern coast of Africa between Somalia and South Africa east to Hawaii and Easter Island. They are also found in the eastern Pacific from the southern Gulf of California to Peru, including many islands such as the Galapagos and Cocos Island. It is a benthopelagic fish which is found at depths between 3 and 182 m in turbid lagoons, over reef flats and in the clear water on rocky and coral reefs.

Biology
Moorish idols feed on sponges, coral polyps, tunicates and other benthic invertebrates. They are normally found in small groups of 2 or 3 individuals but they can also be solitary or gather in large schools. They have a long pelagic larval stage and this is why they are so widespread and geographically uniform. These fishes are pelagic spawners the males and females release sperm and eggs into the water and the eggs drift away on the current following fertilisation.

In the aquarium
Moorish idols are notoriously difficult to maintain in captivity. They require large tanks, often exceeding 380 L, 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 no food and perish, or eat everything all at once.

In popular culture

 * In the 2003 Disney/Pixar animated movie Finding Nemo, a Moorish idol fish named Gill, voiced by Willem Dafoe, is one of Nemo's tank mates and the leader of the Tank Gang. Gill was depicted having a very strong desire for freedom outside of the aquarium and was constantly scheming to achieve this, possibly alluding to the difficulty of keeping real-life Moorish idols in captivity. Gill and the other members of the Tank Gang appeared in the 2016 sequel, Finding Dory, in a post credits scene.
 * Moorish idols have long been among the most recognizable of coral reef fauna. Their image has graced all types of products, such as: shower curtains, blankets, towels and wallpaper made with an ocean or underwater theme.