Parrotfishes are a group of marine species found in relatively shallow tropical and subtropical oceans around the world. With about 95 species, this group displays its largest species richness in the Indo-Pacific. They are found in coral reefs, rocky coasts, and seagrass beds, and can play a significant role in bioerosion.
Parrotfish are named for their dentition, which is distinct from other fish, including other labrids. Their numerous teeth are arranged in a tightly packed mosaic on the external surface of their jaw bones, forming a parrot -like beak with which they rasp algae from coral and other rocky substrates (which contributes to the process of bioerosion ).
Maximum sizes vary within the family, with the majority of species reaching 30–50 cm in length. However, a few species reach lengths in excess of 1 m and the green humphead can reach up to 1.3 m.
(extract from Wikipedia)