Moorish idols are a small reef fish, with a maximum length of 23 cm, and are normally around 21 cm. They are boldly colored with white, yellow, and black vertical bars on their very compressed, disk-like bodies. Moorish idols are diurnal (active during the day) and may be seen alone or in pairs, occasionally forming large schools. Juveniles may be more likely to school in small groups than adults. Adult individuals mate for life, and males will show aggression towards other males. Moorish idols, Zanclus cornutus, feed mainly on encrusted life, including sponges, tunicates, and other invertebrates and algae in the benthic zone (seafloor).