Naso annulatus

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Latin name Naso annulatus - (Quoy & Gaimard, 1825)
Local name Whitemargin unicornfish
Family Acanthuridae - Naso
Origin East Indian Ocean, West Indian Ocean, Australia, Japan, Indonesia, East Pacific, Central/West Pacific
Max length 100 cm (39,4")
As aquarium fish
Minimum volume 0 cm (0 gal)
Hardiness Average
Suitable for aquarium Not suitable for home aquarium
Reef safe Always reef safe
Aggressiveness Might be aggressive towards similar species
Recommended Microalgea (Eg. spirulina)
Macroalgea (Eg. seaweed / nori)
Mostly Small crustaceans (Krill, mysis, artemia...)
Beware of
Demand a very large aquarium when fully grown

This species needs a very large aquarium when fully grown.

Exactly how big the aquarium should be is hard to say, but the size of this species is such, that it cannot normally be kept in a home aquarium.

Keep in mind
Well established aquarium with algae

These fish should be kept in a well run aquarium where they can "graze" algae from rocks and stones.

If there are insufficient algae on the rocks, it is important to feed more frequently and supplement with algae rich food e.g. Spirulina. 

Hiding places

This species needs good hiding places, for example, between live rocks.

Requires plenty of space for swimming.

This species revels in swimming and requires an aquarium with ample space.

Algae Eaters

Even though these fish enjoy a diverse type of frozen foods, it is imperative that its primary food, is algae based, thus ensuring that the fish`s immune system remains healthy.

This can, for example, be plant based fish flakes, Nori seaweed or similar.

Descriptions and further reading
Genus description (Naso)

To thrive, species in the Naso genus, normally demand large aquaria, both because of their size, but also to fulfil their need for swimming space.

Like other Surgeonfish, Naso, or Unicornfish, eats a great amount of algae, which should reflect in their food. They need more algae based food then other species of Surgeonfish, this one must be aware of so as not to create nutrition problems.

When newly introduced Naso can be in the aquarium without eating for some time, but they normally begin to eat within a week.

They are, on the whole a peaceful species in relation to other Surgeonfish.

It is important that one chooses a healthy individual at the petshop, i.o.w. a fish that is active, shows normal behaviour and does not look too thin. If it looks poorly one has a challenge on ones hand, especially when the fish takes its time to start eating.

Some sources report, that large Naso Surgeonfish can in some cases scratch acrylic and glass, since their scalpel grows larger then others of the species.

Family description (Acanthuridae)

Surgeonfish (Acanthuridae) live primarily of different types of algae, making it a popular choice for coral aquariums, as they help to keep the aquarium algae free.

Most Surgeonfish have a scalpel by the caudal fin, used to defend themselves. It can cause some deep lacerations, so pay attention if the fish start to fight and when handling the fish.

When in the aquarium, they will spend most of their time swimming around and nibbling the algae from the stones. Surgeonfish will rarely irritate corals or invertebrates. Large Palettes/Blue tangs can be an exception.

The Surgeonfish are not typically aggressive towards other types of fish. If more Surgeonfish are added to the aquarium, they will establish a hierarchy. It is best to add the most aggressive species last and to ensure that there are sufficient hiding places, as they prefer to have their own individual sleeping area.

If multiple aggressive species are added to the same aquarium, one runs the risk of one of them dying due to stress. One must therefore be cautious about adding multiple Acanthurus species or Zebrasoma xanthurum into the same aquarium. A combination of the different genera will normally get along well, although the more aggressive species can still be challenging.

Aquarium trade Yes
Distribution Indo-Pacific: East Africa, including the Mascarene Islands (Ref. 37792) to the Hawaiian, Marquesan, and Tuamoto islands, north to southern Japan, south to Lord Howe Island.
English common names Unicornfish
Whitemargin unicornfish
White-margin unicorn
Banded unicornfish
Ringtailed unicornfish
Danish common names Hvidkantet næsehornsfisk
References and further reading

About references

Mark Denaro. 2012. The Naso Tang - Tropical Fish Hobbyist - (English)
Bob Fenner. Unicorn Tangs, The Genus Naso, Family Acanthuridae - Wet Web Media - (English)

James W. Fatherree. 2009. Aquarium Fish: Surgeonfishes, A.K.A. the Tangs - Advanced Aquarist - (English)
Bob Fenner. Surgeons, Tangs and Doctorfishes, Family Acanthuridae - Wet Web Media - (English)
2013. Kirurgfisk - Saltvandswiki - (Danish)