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.


  • The unicornfish is easily identified by the bony horn on its forehead, in front of the eyes, though not all species exhibit this horn.
  • There are two plates on either side of the tail with razor-sharp spines (scalpels) that are used both offensively and defensively, against one another in struggles for dominance or against predators.
  • Unicornfishes come in slender, tubular shapes, as well as the more typical flattened form.

Fun Facts

  • The horn-like appendage between the eyes begins growing when a young fish reaches about 5 in (13 cm) in length, and tends to be a little bigger on males.
  • The unicornfish does not use its horn for defense, but rather its sharp tail spines. Biologists are unsure of the purpose of the horn.
  • This fish has the amazing ability to change its color almost instantly depending on its environment and its mood.

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