Acanthuridae

Bluespine unicornfish

Naso unicornis

A forehead horn among surging reefs

• Gray
• Yellow
• Tropical
• Regional distribution
• Marine fish
• Compressed
• Compressed cross-section
• Large
• Tropical fish

Bearing an imposing horizontal forehead horn, the bluespine unicornfish is an iconic, large-bodied acanthurid that roams the current-swept outer reefs of the tropical Indo-Pacific. Its elongated, robust olive-grey body displays a subtle greenish or bluish cast along the flanks, crowned by a distinct cylindrical bony horn that projects forward between the eyes without exceeding the mouth. At the caudal peduncle lie two prominent, fixed bony keels equipped with razor-sharp, forward-curving blue blades that provide formidable lateral defense against predators. Found from the Red Sea and South Africa across northern Australia and Hawaii to French Polynesia, it thrives on shallow wave-exposed reef crests, rocky headlands, and deep seaward walls between one and eighty meters depth. Solitary or moving in small loose groups, this herbivore specializes in grazing tough, leafy brown macroalgae, particularly Sargassum and Dictyota. Diurnal and wary, mature individuals attain impressive recorded maximum total lengths of seventy centimetres.

Sources: Australian Museum — Bluespine Unicornfish, Naso unicornis