Bicolour Parrotfish

Overview

The Bicolour Parrotfish (Cetoscarus bicolor) is a large, striking species endemic to the Red Sea. As a key reef-dwelling herbivore, it plays a vital role in maintaining coral health by grazing on algae and bioeroding reef substrates.

Distribution & habitat

This species is restricted to the Red Sea, where it inhabits clear lagoons and seaward reefs. Juveniles are typically found in sheltered, structurally dense microhabitats like coral rubble or algae-rich areas, while adults are often seen cruising along reef slopes.

Appearance

This fish undergoes dramatic color changes throughout its life. Juveniles are distinctively patterned, featuring a white body with a broad orange band encircling the head and a prominent black spot on the dorsal fin. As they mature, they transition through an initial phase—often dark brown with a large cream-colored patch—to a terminal phase, where adults display vibrant green coloration with pink spotting and fin edging. They possess fused, beak-like dental plates designed for scraping algae from hard surfaces.

Biology & behavior

Cetoscarus bicolor is a sequential hermaphrodite, beginning its life as a female before transitioning into a male. Adults are generally solitary and territorial, often maintaining harems. Like other parrotfish, they are known to sleep in a protective mucus cocoon secreted at night to deter predators.

Feeding

Primarily herbivorous, this species feeds by scraping the epilithic algal matrix from rocky surfaces and dead coral skeletons. Its powerful, fused dental plates allow it to bite deeply into the substrate, consuming algae, detritus, and associated organic matter, which contributes to the creation of carbonate sand on the reef.