Bumpheads parrotfish are one the main attraction during a dive around the Gili Islands. When it is full moon there is a good chance to see them in big groups.
The Bumphead parrotfish is the largest of all parrotfishes, growing to 1.3 meters in length and 100 46 kg in weight. Adults are a dull green, with the front of the head pale yellowish to pink; juveniles are
greenish to brown with five vertical rows of small whitish spots. This species does not display sex-associated patterns of color change. Adults develop a bulbous forehead and their teeth plates are exposed (only partly covered by fleshy lips). The species is slow growing and long-lived (up to 40 years), with delayed reproduction and low replenishment rates
Bumphead parrotfish appear to recruit at low levels throughout the year but are not very selective about
which habitats they settle into. They live in coral reef habitats from 1-30 meter depth in the central
and western Pacific and Indo-Pacific. They occur in barrier and fringing reefs during the day, but
rest in caves or shallow sandy lagoon flats at night. Juveniles are found in seagrass beds inside lagoons while adults are more commonly found in outer lagoons and seaward reefs. This species is gregarious and usually occurs in small aggregations, but group size can be quite large (>75) on seaward and clear, outer lagoon reefs. They sleep in large groups, thus rendering them highly vulnerable to exploitation by spearfishers and netters at night.
Bumphead parrotfish is primarily a corallivore, but also eats benthic algae. They use their large head to ram corals and break them into pieces that are more easily ingested (each fish ingests over 5 tons of structural reef carbonates per year), contributing significantly to the bioerosion of reefs.
Aggregations of this species are important coral sand producers on reefs and may be important in maintaining ecosystem resilience.
They spawn pelagically during a lunar cycle near the outer reef slope or near promontories, gutters, or
channel mouths, and utilize spawning aggregations sites. Courtship and spawning has been reported to occur in early morning, although it may occur at other times.