#acanthuridae

Scribbled Unicornfish Naso maculatus

Paletail unicornfish (Naso brevirostris) off the coast of the Seychelles

The Ap-peel of the Orangespine Unicornfish

Also known as the barcheek unicornfish, the naso tang, or the lipstick tang, the orangespine unicornfish (Naso lituratus) is a common species of fish found in the Indian and Pacific Oceans. They appear only in shallow waters, up to a maximum of 90m, typically in coral reefs or along rocky bottoms. Natively their range stretches from the Red Sea all the way to Hawaii, although some populations have been introduced in the Gulf of Mexico.

This is a very easily identifiable fish; the body is usually light or dark brown, although they can also display blacks, blues, and greens depending on mood and time of day. An orange ventral fin lines the stomach and a black, green, and orange dorsal fin mirrors it along the spine. This species also sports distinctive orange and yellow markings on the face and tail. They typically grow up to 45 cm long, and males and females are about the same size. As with many other tang species, the naso tang has sharp spines at the base of the tail-- also known as the caudal peduncle-- that they can erect when threatened. However, unlike other unicornfish, this species lacks the distinctive “horn” protruding from the forehead.

Common predators of N. lituratus include rays, groupers, lionfish, moray eels, and reef sharks. However, lipstick tang are fast swimmers and often dart into coral or crevices to avoid being eaten. If caught, they can thrash about and strike predators with the spines on their tail. In turn, the lipstick tang feeds mostly on brown algae that grow on corals or the rocky ocean floor. This can help prevent algae overgrowth and helps keep corals healthy. To help them digest the algae, N. lituratus is host to a unique group of bacteria known as Epulopiscium. 

Like most coral reef fish, the orangespine unicornfish is a social species. They can usually be seen swimming in pairs or small schools. N. lituratus reproduces throughout the year, peaking in late spring. Males will attract females by swimming up to them, changing colors, and shimmering. If the female accepts, both individuals swim near the surface of the water and release their gametes which combine in the open ocean. Fertilized eggs then drift with the current, eventually developing into larvae. These larvae congregate in shallow waters and lagoons where they continue to develop until they reach sexual maturity, at about two years old. In the wild, orangespine unicornfish can live up to 14 years.

Conservation status: This species has not been evaluated by the IUCN. Likely threats include by-catch, habitat destruction, and the aquarium trade. The latter is also responsible for introducing the orangespine unicornfish into non-native ecosystems in the Atlantic Ocean, where it is becoming an invasive species.

Photos

Jeff Whitlock

Olha Ukhal

Whitemargin unicornfish (Naso annulatus)