The Diet of the Naso Tang

The naso tang, sometimes called the orangespine unicornfish, is a member of the surgeonfish family inhabiting the western and central Pacific Ocean. The technical ichthyological website FishBase places their range from Japan to Australia's Great Barrier Reef and New Caledonia eastward to the Hawaiian archipelago, French Polynesia, the Pitcairn Islands and Clipperton Island. Strikingly colored and proportioned, the tang's preferred habitat and small, protruding mouth point toward its favored diet: algae.

Basic Diet

Naso tangs are essentially herbivorous, mostly targeting brown algae. Sargassum and Dictyota, two genera of brown algae, are common food items. Other genera mentioned include Turbinaria and Padina in a 1993 University of Guam Marine Laboratory review of naso tang feeding habits in Guam by Meyer et al. According to FishBase, Hawaiian naso tang also eat Lobophora.

Zooplankton

While algae constitutes the great majority of the naso tang's diet, FishBase also suggests that both juveniles and adults will occasionally feed on zooplankton and possibly other invertebrates. Certain other related species of tang also feast on plankton.

Feeding Behavior

The puckered mouth of the naso tang helps it nibble and rake algae from rocky substrate. The fish mainly inhabits reefs and aggregations of marine debris, ranging down up to 90 feet in depth but usually frequenting shallower waters. Staying close to its algal pastures, it often feeds alone or in small gangs, although occasionally it will mass together in larger numbers, according to Randall's Surgeonfishes of Hawai'i and the World as cited by FishBase. According to Kuiter and Tonozuka, young naso tang may congregate with related surgeonfishes. Species in this family typically feed diurnally---during daylight hours---and retreat to shelters amid reefs at night to avoid predators.

Other Notes

The Meyer et al. study out of the University of Guam Marine Laboratory showed naso tang avoided eating seaweeds applied with extracts of five particular types of algae, suggesting the evolution of chemical predatory deterrents. Off Aldabra Atoll, research conducted by Robertson and Polunin and summarized in a 1981 edition of Marine Biology showed the elegant tang, then still classified with the naso tang, mainly tolerated by the powder blue tang and the damselfish Stegastes fasciolatus, but regularly excluded by another tang species, Acanthurus lineatus, from its feeding grounds. All these species overlap somewhat in algal diet and foraging areas.