Naso hexacanthus 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Actinopterygii Perciformes Acanthuridae

Scientific Name: Naso hexacanthus (Bleeker, 1855)
Common Name(s):
English Sleek Unicornfish, Blacktongue Unicornfish, Black Unicornfish, Nohorn Unicorn, Thorpe's Unicornfish
French Nason Jaune, Nason Lisse, Nason Noir
Spanish Barbero Liso
Naseus vomer Klunzinger, 1871
Naso thorpei Smith, 1966
Naso vomer (Klunzinger, 1871)
Priodon hexacanthus Bleeker, 1855

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2012
Date Assessed: 2010-05-06
Assessor(s): Choat, J.H., McIlwain, J., Abesamis, R., Clements, K.D., Myers, R., Nanola, C., Rocha, L.A., Russell, B. & Stockwell, B.
Reviewer(s): Edgar, G. & Kulbicki, M.
Naso hexacanthus is widespread in the Indo-Pacific region. It is common and locally abundant in parts of its range. It is a popular food fish and although common in fish markets and targeted in the Philippines, there is no evidence of population declines due to fishing. It is found in a number of well-policed marine protected areas in parts of its distribution. It has a wide depth range and is generally found in deeper waters. It is therefore listed as Least Concern.

Geographic Range [top]

Range Description:Naso hexacanthus is found from the Red Sea and East Africa including the Mascarene Islands to the Hawaiian, Marquesan and Ducie islands, northwards to southern Japan and southwards to Lord Howe Island. It is reported in the eastern Pacific from Clipperton Island (Robertson and Allen 1996) and Cocos Island.
Countries occurrence:
American Samoa; Australia; British Indian Ocean Territory; Brunei Darussalam; Cambodia; China; Christmas Island; Cocos (Keeling) Islands; Comoros; Cook Islands; Costa Rica (Cocos I.); Disputed Territory (Paracel Is., Spratly Is.); Djibouti; Egypt; Eritrea; Fiji; France (Clipperton I.); French Polynesia; French Southern Territories (Mozambique Channel Is.); Guam; India (Andaman Is., Nicobar Is.); Indonesia; Israel; Japan; Jordan; Kenya; Kiribati (Gilbert Is., Kiribati Line Is., Phoenix Is.); Madagascar; Malaysia; Maldives; Marshall Islands; Mauritius; Mayotte; Micronesia, Federated States of ; Mozambique; Myanmar; Nauru; New Caledonia; Niue; Northern Mariana Islands; Oman; Palau; Papua New Guinea; Philippines; Pitcairn; RĂ©union; Samoa; Saudi Arabia; Seychelles; Singapore; Solomon Islands; Somalia; South Africa; Sudan; Taiwan, Province of China; Tanzania, United Republic of; Thailand; Timor-Leste; Tokelau; Tonga; Tuvalu; United States (Hawaiian Is.); United States Minor Outlying Islands (Howland-Baker Is., Johnston I., Midway Is., US Line Is., Wake Is.); Vanuatu; Viet Nam; Wallis and Futuna; Yemen
FAO Marine Fishing Areas:
Indian Ocean – western; Indian Ocean – eastern; Pacific – northwest; Pacific – southwest; Pacific – western central; Pacific – southeast; Pacific – eastern central
Additional data:
Lower depth limit (metres):229
Upper depth limit (metres):6
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Naso hexacanthus is not common in depths less than about 15 m, but abundant in deeper water, particularly near escarpments (Randall 2001b). It was recorded as occasional in terms of relative abundance in the northern Bismarck Sea, Papua New Guinea (Allen 2009), occasional but locally common to abundant in Milne Bay Province, Papua New Guinea (Allen 2003). It is moderately common at Raja Ampat, Indonesia (Allen 2003b). It is uncommon in the American Samoa National Park (National Park of Samoa Checklist of Fishes accessed 21 April 2010). It is common in drop-offs in Palau (R. Myers, pers comm. 2010). It is common and locally abundant in the Philippines (R. Abesamis and B. Stockwell pers. comm. 2010).

In the Apo Island, Philippines fishery beginning March and through August - it is abundant in catch when it is the season for small jellyfish, and spearfishers can catch N. hexacanthus using breathhold spearfishing at night during the new moon. Hook and line is used during the day. During the peak in jellyfish season (June-July) fishers can land up to 60 kg. (3 fishers). The one fisher average is of 10 fish (A. Candido pers. comm. 2010).

It is uncommon in Guam (J. McIlwain unpub. data). It is not recorded in the Pohnpei fishery in 2007 (Rhodes et al. 2008). In Hawaii an average of 1,400 kg/year is harvested. N. hexacanthus is the sixth most important Acanthurid species (Division of Aquatic Resources unpub. data). It is a commercial species in the Tuamotos and French Polynesia (de Loma et al. 2009). 
In Kenya, landings during 1978-2001 for families that are less important in commercial catches (e.g., scarinae and Acanthuridae) showed rising catches (1978-1984) followed by a general decline during the 1990s, but the landings for the scarinae showed a rising trend in recent years (Kaunda-Arara et al. 2003).
Current Population Trend:Stable
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:Naso hexacanthus is often seen in large aggregations. It feeds on the larger animals of the zooplankton such as crab larvae, arrow worms and pelagic tunicates (Randall 2001b). The diet of this species consists almost exclusively of large gelatinous plankton. Juveniles feed on macroscopic and turf algae and strongly associated with reef substrata. It is herbivorous up to age 2 years. Juveniles are more common in mid-shelf reefs (Choat et al. 2002).  
The number of sagital increments in a study done by Choat and Axe (1996) suggest that members of the genus Naso attain the same maximum ages as the other Acanthurids, in excess of 40 years for this species. Maximum age 44 years (Choat and Robertson 2002a).


The sexes are separate among the acanthurids (Reeson, 1983). Males have characteristic mating colours when courting in open water. Caudal knives in males are enlarged (J.H. Choat pers. comm. 2010). This species was observed to form spawning aggregations on the Great Barrier Reef (Johannes 1981). Size at sexual maturity 450 mm (Choat and Robertson 2002a).

Use and Trade [top]

Use and Trade: Although abundant in many localities and a good food fish, the landings are relatively low due to difficulty in capturing it. It is taken mainly in traps (Randall 2001b). It is also harvested using spear and hook and line (A. Candido pers. comm. 2010). It is found in fish markets in the Coral Triangle Region (J.H. Choat pers. comm. 2010).

Threats [top]

Major Threat(s): Naso hexacanthus is a targeted food fish in parts of its range.

Surgeonfishes show varying degrees of habitat preference and utilization of coral reef habitats, with some species spending the majority of their life stages on coral reef while others primarily utilize seagrass beds, mangroves, algal beds, and /or rocky reefs. The majority of surgeonfishes are exclusively found on coral reef habitat, and of these, approximately 80% are experiencing a greater than 30% loss of coral reef area and degradation of coral reef habitat quality across their distributions. However, more research is needed to understand the long-term effects of coral reef habitat loss and degradation on these species' populations. Widespread coral reef loss and declining habitat conditions are particularly worrying for species that recruit into areas with live coral cover, especially as studies have shown that protection of pristine habitats facilitate the persistence of adult populations in species that have spatially separated adult and juvenile habitats (Comeros-Raynal et al. 2012).

Conservation Actions [top]

Conservation Actions: There are no species-specific conservation measures in place for this species. However, its distribution overlaps several marine protected areas within its range.

Citation: Choat, J.H., McIlwain, J., Abesamis, R., Clements, K.D., Myers, R., Nanola, C., Rocha, L.A., Russell, B. & Stockwell, B. 2012. Naso hexacanthus. The IUCN Red List of Threatened Species 2012: e.T178002A1517273. . Downloaded on 15 October 2018.
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