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.
The Moorish idol is the only extant member of its family, the Zanclidae, making it a relict. A number of extinct relatives are known.
Etymology
The Moorish idol's unusual common name was apparently given to it because, in some areas of southeast Asia, fishermen have respect for these fishes, releasing them when caught and honouring them with a bow after their release. In this case, "Moor" is erroneously used as it usually refers to Amazigh people from Morocco where this fish does not occur in the wild, although this term may be related to the practice of referring to muslims in Sri Lanka and India as "Moors" during the colonial period.
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.
Distribution
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.
Description
The Moorish idol's body is highly laterally 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. They are normally found in small groups of 2 or 3 individuals but they can also be solitary or gather in large schools.
Reproduction
These fish are pelagic spawners. The males and females release sperm and eggs into the water, and the eggs drift away on the current following fertilization. The preflexion larval stage of the Moorish idol has no fin spines, soft rays, or internal support structures for the fins. However, in a 3.2 mm specimen there is the start of the dorsal and anal fins. The larger preflexion specimens have mostly cartilaginous supraoccipital crests with 23 to 26 curved dorsal spines. Also, pigmentation increases with size in the preflexion larvae. The postflexion larval stage refers to the stage that includes the formation of the caudal fin and fin rays. This is the stage right before juvenile and settlement into their habitat.
A great diversity of large predatory fish species take this opportunity to hunt the aggregations while they are still on the reef, often forming multi-species hunting packs. This notably includes packs of hundreds of grey reef sharks, which will also follow the Moorish idols when a school moves away from the safety of the reef to spawn. Once the Moorish idols enter the open water, the grey reef sharks attack in a tight cluster and enter a feeding frenzy, eventually eating most of the school. Only a few Moorish idols in a school may survive the sharks. As a result of the extremely high mortality rate, these spawning events have been described as seeming "suicidal".
Conservation status
Since their last assessment in 2015, the Moorish idol is listed as a species of least concern by the IUCN. They were found to be widely distributed and locally abundant with no major threats to the species.
In the aquarium
thumb|right|Comparison between the Moorish idol (left), [[schooling bannerfish (top) and pennant coralfish (bottom)]]
Moorish idols are notoriously difficult to maintain in captivity. They require large tanks, often exceeding , are voracious eaters, and can become destructive.
- 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.