Moorish

Zanclus cornutus

Family: Zanclidae | Genus: Zanclus

The  Moorish idol (Zanclus cornutus) is a marine fish that inhabits coral and rocky reefs, recognised for its flattened body shape and its elongated, whip-like dorsal fin.

It displays striking black, white and yellow vertical bands, with a distinctive yellow and black “saddle” over its snout. Its small mouth and tubular snout allow it to graze on sponges and encrusting invertebrates attached to rocks. The species can reach up to 23 cm in length and is highly valued in aquariums.

Geographical distribution

The Moorish idol is widely distributed across the Indo-Pacific Ocean, including the coasts of East Africa, Australia, Japan, the Philippines, Hawaii and Micronesia, as well as the Eastern Pacific, from southern California to Peru and many oceanic islands. This wide distribution is closely linked to its extended pelagic larval phase, which facilitates dispersal over long distances.

Habitat

This species lives mainly in coral and rocky reefs of the Indo-Pacific and Eastern Pacific — marine ecosystems renowned for their rich biodiversity.
It thrives in reef zones characterised by:

Clear waters of varying depths: Found in tropical waters ranging from crystal clear to slightly turbid, at depths between 3 and 182 metres.
Rocky and coral substrates: Uses coral and rock structures for shelter and feeding, as these environments host the sponges and invertebrates it consumes.
Inner lagoons: Common in lagoons protected by the reef, where currents are gentle and benthic life is abundant.
Reef slopes and edges: Seen along outer reef slopes and drop-offs, where prey availability increases.
High biodiversity: Coexists with a variety of fish, invertebrates and corals, contributing to a balanced, complex ecosystem in which it plays a specific ecological role.

The Moorish idol is highly sensitive to environmental changes, depending on the health and stability of coral and rocky reefs. Its presence serves as an indicator of reef quality and biodiversity.

Lifestyle and behaviour

The Moorish idol is non-territorial, though it may show aggression towards other species in close quarters.

Social behaviour:

Usually found in small groups of 2–3 individuals, but may also appear solitary or in larger schools, especially during the juvenile stage.

Its vivid colour pattern provides “disruptive colouration”, a camouflage strategy that helps confuse predators.

Adults often form long-term pairs and may display pair-defence behaviour against intruders.

Daily activity:

Diurnal species, active during daylight hours and resting near the seabed at night.

Curiosity:

The long white dorsal fin, resembling a whip, can regenerate if damaged by predators or accidents.

Reproduction:

Oviparous species with pelagic spawning: males and females release gametes into the water column, and fertilised eggs drift with ocean currents.
The larvae remain pelagic for an extended period before settling on the reef — a key factor explaining their wide distribution.
No parental care is provided.

Diet

In the wild

Sponges, tunicates, ascidians and bryozoans (main food sources, up to 70% of diet)
Small benthic invertebrates
Some molluscs and hydrozoans
Minor intake of benthic algae

Under human care

Prepared sponge-based foods, seaweed leaves, and small crustaceans such as Mysis.
Highly demanding and delicate in captivity; often refuses dry foods and requires a varied, frequent diet to stay healthy.

Conservation status

The Moorish idol (Zanclus cornutus) is listed as Least Concern (LC) by the IUCN Red List, with stable populations overall, though it is occasionally caught for the aquarium trade. Its survival depends on the health of coral reefs, making it vulnerable to habitat degradation caused by pollution and climate change.

Main threats:

Degradation of coral and rocky reefs.

Sensitivity to changes in water quality and global stressors (pollution, acidification) affecting both habitat and food availability.