Photo copyright Tim Nicholson.
Taken at Cabo Pulmo, Baja California.
Moorish Idol, Zanclus cornutus

Moorish Idols change to a darker colour at night, to reduce their chances of being spotted by nocturnal predators. The darker hues blend in with the gloom and help to break up their outline.

It has a long snout with which it feeeds on coralline algae and sponges in cracks and crevices of the reef.

You see it in ones, twos or large groups in the Indian and Pacific Oceans. It's not found in the northern Red Sea though. They are very easy to recognise, with their daytime black, white and yellow colours and distinctive orange band over the nose. They live between 3 and 180 m.

The Moorish Idol is the only species in the family Zanclidae. The common name, Moorish Idol, is said to get its name from the Moors of Africa who purportedly believed the fish to be a bringer of happiness.

Like the butterfly fish, Moorish Idols mate for life.

Further Reading
Coral Reef Fishes, Indo-Pacific and Caribbean , by Ewald Lieske and Robert Myers, Harper Collins