Naso is a genus of marine ray-finned fishes belonging to the family, Acanthuridae, the unicornfishes, surgeonfishes and tangs. The fishes in this genus are known commonly as unicornfishes because of the "rostral protuberance", a hornlike extension of the forehead present in some species.
Unicorn fish are popular with spearfishermen and may be cooked by grilling them whole. Unicornfish primarily live around coral reefs and eat mostly algae.
This genus is distributed across the Indo-Pacific from Africa to Hawaii.
Taxonomy
Naso was first proposed as a genus in 1801 by Bernard Germain de Lacépède when he described Naso fronticornis as a new species from Jeddah and Mauritius. In 1917 David Starr Jordan designated Naso fronticornis as the type species of the genus Naso. within the family Acanthuridae.
Etymology
Naso means "nose" referring to the fleshy protuberance on the forehead of N. fronticornis (=unicornis). The subgenus Axinurus comes from axino and oura, meaning axe-tail, potentially referring to the presence of a single tail spine on each side as opposed to two in the subgenus Naso.
The species in the genus Naso vary in size from a maximum published standard length of in the slender unicorn (N. minor) to a maximum published total length of in the whitemargin unicornfish (N. annulatus).
Biology
Naso unicornfishes differ from other acanthurids in that they eat zooplankton rather than grazing on algae or detritus and that they tend to live at greater ranges of depth.
Molecular phylogenetics show that horns independently evolved multiple times within the genus, and only ever evolved in benthic feeding species. Similarly, benthic-feeding also evolved multiple times independently. In addition, pelagic feeding and the fast-swimming "scombriform" body shape appear to be plesiomorphic traits. This is because the basalmost species in Naso are the pelagic feeding "scombriform" species in the subgenus Axinurus, and because every other acanthurid genus comprises predominantly benthic feeders.
In some species, both males and females display such a horn. In at least some species where this is the case, such as the bluespine unicornfish, the horn is slightly sexually dimorphic, being slightly larger in males. and 20 species are classified within it:
{| class="wikitable"
|+Subgenus Naso <small>Lacepède, 1801</small>
!Species
!Common name
!Image
|-
|Naso annulatus
<small>(Quoy & Gaimard, 1825)</small>
|whitemargin unicornfish
|frameless
|-
|Naso brachycentron
<small>(Valenciennes, 1835)</small>
|humpback unicornfish
|frameless
|-
|Naso brevirostris
<small>(G. Cuvier, 1829)</small>
|spotted unicornfish
|frameless
|-
|Naso caesius
<small>J. E. Randall & Bell, 1992</small>
|gray unicornfish
|frameless
|-
|Naso elegans
<small>(Rüppell, 1829)</small>
|elegant unicornfish
|frameless
|-
|Naso fageni
<small>Morrow, 1954</small>
|horseface unicornfish
|frameless
|-
|Naso hexacanthus
<small>(Bleeker, 1855)</small>
|sleek unicornfish
|frameless
|-
|Naso lituratus
<small>(J. R. Forster, 1801)</small>
|orangespine unicornfish
|frameless
|-
|Naso lopezi
<small>Herre, 1927</small>
|elongated unicornfish
|frameless
|-
|Naso maculatus
<small>J. E. Randall & Struhsaker, 1981</small>
|spotted unicornfish
|
|-
|Naso mcdadei
<small>J. W. Johnson, 2002</small>
|squarenose unicornfish
|frameless
|-
|Naso reticulatus
<small>J. E. Randall, 2001</small>
|reticulated unicornfish
|frameless
|-
|Naso tergus
<small>H. C. Ho, K. N. Shen & C. W. Chang, 2011</small>
|Taiwanese unicornfish
|
|-
|Naso tonganus
<small>(Valenciennes, 1835)</small>
|bulbnose unicornfish
|frameless
|-
|Naso tuberosus
<small>Lacépède, 1801</small>
|humpnose unicornfish
|frameless
|-
|Naso unicornis
<small>(Forsskål, 1775)</small>
|bluespine unicornfish
|frameless
|-
|Naso vlamingii
<small>(Valenciennes, 1835)</small>
|bignose unicornfish
|frameless
|}
{| class="wikitable"
|+Subgenus Axinurus <small>Cuvier 1829</small>
!Species
!Common name
!Image
|-
|Naso caeruleacauda <small>J. E. Randall, 1994</small>
|blue unicornfish
|frameless
|-
|Naso minor <small>(J. L. B. Smith, 1966)</small>
|slender unicornfish
|frameless
|-
|Naso thynnoides <small>(G. Cuvier, 1829)</small>
|oneknife unicornfish
|frameless
|}