The mouth of this fish (like other surgeonfishes) is perfectly designed to carefully remove the algae from coral while leaving the coral intact.
Algae needs an abundance of oxygen and sunlight to thrive, which makes the shallow coral reefs of the tropics a perfect place for algae to multiply. Left undisturbed, algae would soon blanket the coral in a carpet of green and the coral would soon die. To the rescue come algae-eaters like the unicornfish. The mouth of this fish (like other surgeonfishes) is perfectly designed to carefully remove the algae from coral while leaving the coral intact. Its fine row of sharp, small teeth make short work of the algae.
CLASS: Actinopterygii (ray-finned fishes)
ORDER: Perciformes (perch-like fishes)
FAMILY: Acanthuridae (surgeonfishes and unicornfishes)
GENUS/SPECIES: Naso (19 species)
Size: Up to 2 ft (61 cm)
Depth: 15–150 ft (5–45 m)
Diet: Zooplankton and algae
Habitat: Indo-Pacific; from Hawaii to Indian Ocean, up into the Red Sea