Sleek Unicornfish

Blacktongue Unicornfish ~ Unicorn Tang

Family: Acanthuridae Picture of a Sleek Unicornfish or Blacktongue Unicornfish, Naso hexacanthusNaso hexacanthusPhoto © Animal-World: Courtesy David Brough

   We have seen these fish available only rarely. Unlike other unicornfish, neither the male nor the female Sleek Unicornfish will develop horns!

   The Sleek Unicornfish is also called the Blacktongue Unicornfish or Unicorn Tang. Though it doesn't develop a horn like other members of the Naso genus (unicornfish), when it reaches just under 10 inches (25 cm) in length it does develop a black tongue. This is probably the largest tang to be sold in the aquarium industry (over 2 1/2 feet in length). Though a flashy and impressive display fish only the largest tanks can house it.

   All the species in the Naso genus are peaceful fish. They get along with most other marine fish and can be kept with a variety of tank mates including other genus' of surgeonfish. However unless you have a huge (hundreds of gallons) system, it is best to house just one Naso tang to a tank. The Sleek Unicornfish not considered reef safe as this big rambunctious fish will topple corals while swimming about in fast clips. Though it may eat some algae it will very likely nip on invertebrates as well. This pretty specimen is most suitable for an extremely large show tank or a public aquarium.

   The Sleek Unicornfish requires a lot of water turbulence highly saturated with oxygen rather than a placid aquarium. Being very active during the day they need a large tank with plenty of room to swim, but will also need some rocks/ corals with crevices for retreat and to sleep in at night. In the ocean they feed on zooplankton and filamentous algae. Aquarium fare can include such things as various worms, shrimps, and algae. Once they get acclimated and become accustom to aquarium foods they are quite hardy and good eaters.

For more Information on keeping marine fish see:
Guide to a Happy, Healthy Marine Aquarium

Advertise With Us

Geographic Distribution
Naso hexacanthus
Data provided by
  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Actinopterygii
  • Order: Perciformes
  • Family: Acanthuridae
  • Genus: Naso
  • Species: hexacanthus
Pet Supply Comparison Shopping

Habitat: Natural geographic location:   The Sleek Unicornfish or Blacktongue Unicornfish was described by Bleeker in 1855. They are found in the Indo-Pacific from the Red Sea and east Africa to Japan, Lord Howe Island,Hawaii, the Marquesas and Dulcie Island.
   In their natural habitat they are found at depths between 20 - 490 feet (6 - 150 meters). Usually they live in schools in clear steeply sloped lagoons and seaward reef slopes. These are areas swept with ocean currents providing highly oxygen saturated waters and carrying planktonic foods. Naso species will usually be within 32 to 65 feet (10 - 20 meters) of the reef where they can quickly retreat if necessary.

Status:    These fish are not listed on the IUCN Red List.

Description:    The Sleek Unicornfish or Blacktongue Unicornfish has an elongated body shape with a narrower caudal peduncle, features that distinguish this genus from other Acanthurids. They have a grayish to green body that is paler on the lower portion and through the anal fin. There is a yellowish brown tone just in front of the gill cover and the caudal fin is bluish, paler on the end. Unlike other unicornfish they do not develop a protruding horn, not even a bump. However true to their name 'Blacktongue', they do develop a black tongue when it they reach just about 10 inches (25 cm). Juveniles are similar but with a slightly concave edge to the caudal fin.
   Like all Naso species, they have the ability to quickly and dramatically change, depending on mood or environment. When trying to impress a female or indicate anger/ dominance, the male will have a large radiant pale blue area on the head and neck along with blue spots and stripes on the side.
   On each side of the caudal peduncle are two fixed spines or "scalpels" used for defense or dominance. Having one or two fixed blades are what places the Naso genus in the subfamily Nasinae. Caution needs to be exercised when handling surgeonfish as a cut from its scalpel can cause discoloration and swelling of the skin with a high risk of infection. The pain lasts for hours then still ends up having a dull ache. These fish are best captured using a double bag under water, rather than a net.

Length/Diameter of fish:    Adults reach 29 1/2 inches (75 cm).

Maintenance difficulty:    Once eating, Sleek Unicornfish are hardy and moderately easy to maintain as long as sufficient space is provided. Obtain a specimen that is at least 4" long as smaller ones rarely adapt to living in captivity. As they attain around 80% of their growth in the first 5 years of life, this means they are growing at a rate of approximately 4" per year. Space cannot be emphasized enough, as these large restless fish will neither thrive nor survive in too small an environment. They must be housed in a very large tank. It is best not to purchase small with the idea of "getting a bigger tank" later, as these fish will quickly outgrow a smaller tank. Too small of an environment can stunt their growth and they can develop 'behavior problems'. A healthy unicornfish will be swimming the length of the tank during the day. If you see any sulking, hiding behavior, this is an indication of stress. If their reason for sulking is not resolved or they are stressed for too long they may not recover.
   They can handle a wide range of water parameters but will do best in an environment that provides vigorous water turbulence along with consistency, not only in water conditions and quality, but also in decor and fellow inhabitants. They can be housed in a fish only tank, but are not considered reef safe. This big rambunctious fish will topple corals while swimming about in fast clips. Though it may eat some algae it will also very likely nip on invertebrates.
     Naso tangs are continuous feeders and they need to be provided a proper diet. They are susceptible to nutritional disorders which may cause color loss and LLD (lateral line disease). Supplementing their diet with the addition of vitamin C to their food or adding a vitamin supplement directly to their water can help to avoid or aid in reducing these ailments. They are also susceptible to bacteria resulting from organic buildup which deteriorates water quality. Consequently they will need vigorous filtration, protein skimming, and regular small water changes.
   Many of the Acanthuridae members are very colorful, active, and attractive to aquarists. But they do not produce as much skin mucus on their bodies as other fish and can be susceptible to diseases such as Marine Ich and Marine Velvet. Surgeonfish are definitely a candidate for quarantine when you first receive them. They can be treated successfully with medical care or copper drugs, but because they have an important microfauna in their digestive system, prolonged or continuous use of a copper treatment is not advisable.
   In the wild a cleaner wrasse (Labroides sp.) will help them by taking parasites from their bodies, however these wrasses are extremely difficult to sustain in captivity. Alternative fish such as Neon Gobies (Gobiosoma sp.) or cleaner shrimp can help them by providing this cleaning service in the home aquarium.

Diseases that Surgeonfish and Tangs are susceptible to:
Marine Ich (white spot disease), Marine Velvet
and Lateral Line Erosion (LLE)

Foods:    The Sleek Unicornfish or Blacktongue Unicornfish are considered to be planktivorous In the wild these fish range over large areas of steep reefs, occasionally picking at filamentous algae, but primarily feeding on large zooplankton like crab larvae, arrow worms, and pelagic tunicates in the open waters.
   In the aquarium provide various worms, live brine shrimp, mysis, larger shrimps, and euphausiids along with live marine algae (attached or free-floating) and dried algae. You can also offer chunks of prepared frozen formulas containing algae or spirulina, zooplankton, frozen brine and mysis shrimp, and flakes. Japanese Nori or other seaweed can be adhered to the aquarium glass with a vegetable clip. Feed at least 2 to 3 times a day.
   Providing a vitamin supplement (including vitamin C) can help provide for their nutritional needs, and vitamin C can help prevent or reduce Lateral Line Erosion (LLE). This can be done by soaking dried pellets with liquid vitamins, adding vitamins to the food, or adding a liquid vitamin into the water. It is also said that pellets soaked in garlic may help fend off Marine Ich. Some hobbyists also report success with supplemental foods such as previously boiled or frozen zucchini, broccoli, spinach, and leaf lettuce.

Maintenance:    A quick and agile swimmer it will spend a good deal of its time in the open water and moving in and out of crevices. They may jump out of an open aquarium, so be sure to have a lid. Frequent water changes are not necessary, rather normal water changes at 10% biweekly or 20% monthly are fine.
   For more information see, Marine Aquarium Basics: Maintenance

Aquarium Parameters:
   There are some Acanthuridae members that are delicate and will require more specific care, but most will respond well if you employ a few technical considerations. All surgeonfish need an aquarium with plenty of aeration, a strong current will help to provide good oxygenation. Provide a large tank with plenty of space for swimming, especially for adult specimens, along with lots of rocks/ corals with crevices for retreating and for sleeping. This decor will lend itself to algae growth which these fish will enjoy grazing on.
Minimum Tank Length/Size:
   A minimum180 gallon (680 liters), even more for an adult. Too small of an environment can stunt their growth and they can develop 'behavior problems'.
Light: Recommended light levels
   It nature it is found in sunlit and moderate light zones. It can be kept under normal lighting conditions in the aquarium, but can also be kept under very bright light as long as some dimly lit spaces are provided.
   This species lives in tropical areas. Temperatures between 75 - 82° F (24 - 28° C) will serve them well.
Water Movement: Weak, Moderate, Strong
   Strong brisk water movement. All surgeonfish and tangs thrive with good water movement, need lots of oxygen, and love to have the water rushing over their gills. Provide turbid water conditions for this species.
Water Region: Top, Middle, Bottom
   It will spend time in the open water and darting in and out of the rocks/ corals. It will sleep in crevices at night.

Social Behaviors:    The great thing about all the species in the Naso genus is they are quite peaceful and unobtrusive making them an excellent addition to a community aquarium. The Sleek Unicornfish get along with most other marine fish and can be kept with a variety of tank mates including other genus' of surgeonfish. However unless you have a huge (hundreds of gallons) system, it is best to house just one Naso tang to a tank. It is not considered reef safe as this big rambunctious fish will topple corals while swimming about in fast clips. Though it may eat some algae it will very likely nip on invertebrates as well.
   Surgeonfish and tangs can be territorial, sometimes just with their own kind and sometimes with other species. Introducing a new surgeonfish into an aquarium that already houses one or more is usually a problem. It is best to initially introduce several species together rather than adding a new one later on. Though a large aquarium can help alleviate many problems, be aware of the social behaviors of any species you are considering to prevent compatibility problems.
   At times you may put surgeonfish and tangs together with different genus' as long as there are no similarities. For example a large tank can house a Unicornfish, a sailfin tang, and a Hippo Tang without incident. Adding them together initially works best. When adding a new member to an established group, changing the rock work will often alleviate any aggression to the "new guy". A little chasing will occur, but usually nothing detrimental.

Sex: Sexual differences:    No sexual difference is noted for this species. In general males of the Naso species will be larger and the caudal peduncle will be larger and more pronounced than on the females. On some species the tail is also longer.

Breeding/Reproduction:    Some species of surgeonfish have spawned in public aquariums and there have been a few scattered reports of spawning in home aquariums, but regular spawning and the rearing of the young has not yet been reported.
   Though the Sleek Unicornfish has not yet been bred in captivity, the Unicornfish spawn in pairs in the open water. The males can change part of their body into a brilliant color to court a female. A pair will rise to the surface to release their gametes. The eggs are pelagic with an extended larval phase, which probably accounts for the vast distribution of the Unicornfish.
   For more information on breeding and the development of the fry, see: Marine Fish Breeding: Tangs.

Availability:    The Sleek Unicornfish or Blacktongue Unicornfish is generally rarely available and is moderately expensive.

Author: Clarice Brough, CFS
Lastest Animal Stories on Sleek Unicornfish