Bluespine Unicornfish

The Bluespine Unicornfish, known scientifically as Naso unicornis, is a tropical marine fish associated with coral reefs. It thrives at depths ranging from 1 to 180 meters (3 to 590 feet). Fully grown, this fish can reach a maximum length of 70 centimeters (about 28 inches), although it is commonly found at around 50 centimeters (about 20 inches). The oldest known individuals can live up to 55 years.

In the wild, adult Bluespine Unicornfish typically inhabit channels, moats, lagoons, and seaward reefs where the water surges strongly. They are generally found swimming in small groups but can also be solitary. Juveniles tend to stay in shallow, protected areas like bays and harbors. These fish are active during the day and primarily feed on coarse leafy brown algae such as Sargassum. They reproduce through pair-spawning.

The physical characteristics of the Bluespine Unicornfish are distinctive. Adults have a tapering, bony horn on their forehead, which starts as a bump when they are about 12 cm (5 inches) long. This horn projects at the level of the eyes but does not extend past the mouth. The fish has six dorsal spines, between 27 and 30 dorsal soft rays, two anal spines, and 27 to 30 anal soft rays. The body depth changes from about twice the standard length in subadults to 2.4-2.6 times in adults. The tail fin, or caudal fin, is emarginate in youth and becomes truncate with filamentous lobes as they mature. Males typically develop longer horns and larger peduncular features than females of the same size.

Color-wise, the body of the Bluespine Unicornfish is yellowish to olivaceous gray on top and paler underneath, with distinctive blue peduncular plates and spine keels. Their lips are whitish or blue, and some areas around the pectoral fin are also blue. The dorsal and anal fins are yellowish with narrow blue edges, while the caudal fin is orange at the base, transitioning to gray, with a broad, pale greenish back edge trimmed with blue filaments. A noticeable transient color phase includes a blotchy pale greenish zone below the dorsal fin.

Geographically, the Bluespine Unicornfish is found throughout the Indo-Pacific, ranging from the 🌊 Red Sea and East Africa to the Hawaiian, Marquesas, and Tuamoto Islands (🇵🇫 French Polynesia). Its range extends north to southern 🇯🇵 Japan and south to the Lord Howe and Rapa Islands, with the potential presence in 🇸🇴 Somalia requiring confirmation. The genus name "Naso" is derived from the Latin word for nose, referencing the prominent horn on its forehead.