Animal Species:Ringtail Unicornfish, Naso annulatus (Quoy & Gaimard, 1825)

When the Ringtail Unicornfish is about 20 cm in length a long horn develops from a bump anterior to the eye. The species occurs in tropical marine waters of the Indo-Pacific.

Ringtail Unicornfish, Naso annulatus

Ringtail Unicornfish, Naso annulatus
Photographer: Carl Bento © Australian Museum

Standard Common Name

Ringtail Unicornfish

Alternative Name/s

Short-horned Unicorn-fish, White-margin Unicorn


The body of the Ringtail Unicornfish tapers to a narrow caudal peduncle. There are two scutes on the caudal peduncle, each bearing a strong keel. When fish are about 20 cm in length a long horn develops from a bump anterior to the eye. The horn of mature fish can be as long as the head. The species is brown to grey or blackish. Juveniles often have a white ring around the caudal peduncle. The caudal fin margin and membranes of adults are white.

Size range

The species grows to 1 m in length.


It occurs in tropical marine waters of the Indo-Pacific. In Australia this species is known from the offshore islands of north-western Western Australia, the entire length of the Great Barrier Reef, Queensland and Lord Howe Island.

The map below shows the Australian distribution of the species based on public sightings and specimens in Australian Museums. Click on the map for detailed information.  Source: Atlas of Living Australia.

Naso annulatus

Distribution by collection data

Ozcam map of Ringtail Unicornfish specimens in the Australian Museum.

What does this mean?


Juveniles can be found on reefs around shallow lagoons. Adults are usually seen in small schools at depths over 20 m on reef dropoffs.



What does this mean?


  1. Allen, G.R. 1997. Marine Fishes of Tropical Australia and South-east Asia. Western Australian Museum. Pp. 292.
  2. Hoese, D.F., Bray, D.J., Paxton, J.R. & G.R. Allen. 2006. Fishes. In Beesley, P.L. & A. Wells. (eds) Zoological Catalogue of Australia. Volume 35. ABRS & CSIRO Publishing: Australia. parts 1-3, pages 1-2178.
  3. Kuiter, R.H. & H. Debelius. 2001. Surgeonfishes, Rabbitfishes and their relatives. A Comprehensive Guide to Acanthuroidei. TMC Publishing. Pp. 208.
  4. Myers, R.F. 1999. Micronesian Reef Fishes. Coral Graphics. Pp. 330.
  5. Randall, J.E., Allen, G.R. & R.C. Steene. 1997. Fishes of the Great Barrier Reef and Coral Sea. Crawford House Press. Pp. 557.

Mark McGrouther , Collection Manager, Ichthyology
Last Updated:

Tags Ichthyology, Ringtail Unicornfish, Naso annulatus, Acanthuridae, fishes, black, brown, odd-shaped, > 1 m, no-pattern, reef, marine, adult, long head horn,


Mark McGrouther - 3.04 PM, 12 April 2011

Hi Tom.  I have just heard back from Rudie Kuiter who informed me that the fish is probably a juvenile Humpnose Unicornfish, Naso tonganus.  Rudie pointed out that both species have a white ring around the caudal peduncle but that of Naso annulatus is usually more diffused.  I have looked at images of juveniles of both species and that certainly seems to be the case.  N. tonganus is a 'new species' for the site, so I will take your image and work it up into a proper image asset soon.  I'll let you know when it goes online.  Thank you for your contribution.  By the way, I know it looks a bit strange, but it was me who answered your last enquiry as Rebecca Field.  Your enquiry came through to her account. Cheers, Mark.

Rebecca Field - 8.04 AM, 07 April 2011

Hi Tom,  You may well be right, but if so, the fish is well south of its 'recognised' distribution.  See the map on the AFD site. I will consult an expert in the group and post a reply when I hear back.  As the saying goes ... watch this space.

tomdavis - 9.04 AM, 06 April 2011
Hi Mark I have been seeing a few of these juvenile surgeonfish in Nelson Bay in recent months. I wondered if they might be Naso annulatus?

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