Bluespine Unicornfish
Unicorn Tang

Longhorn Unicornfish ~ Longnose Unicornfish

Family: Acanthuridae Picture of a Bluespine Unicornfish or Unicorn Tang, Naso unicornisNaso unicornisPhoto © Animal-World: Courtesy Pavaphon Supanantananont
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I am looking foe Bluespine Unicornfish  Anna Baran

   Despite its large size, the Bluespine Unicornfish is one of the most personable and friendly surgeonfish, once it gets comfortable it will even taking food from its keepers hand!

   The species in the Naso genus, the unicornfish, are all known to be peaceful fish and the Bluespine Unicornfish or Unicorn Tang is one of the most mellow. Though it will constantly be on the move during the day, it will spend its time surveying the decor and munching on algae growths. It will be a little shy at first, but will adapt well to captivity if given it lots of room to roam around in and plenty of naturally growing algae. Once eating it can be offered a variety of algae based aquarium fare for its basic diet, along with some meaty foods.

   The Bluespine Unicornfish is one of the largest fish to be sold in the aquarium industry (over 2 feet in length) so only the largest tanks can house it. It has an amicable nature and will get along with most other marine fish. It 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.

   Like all surgeonfish and tangs, the Bluespine Unicornfish likes a lot of water turbulence rather than a placid aquarium. Being very active during the day they need a large tank with plenty of room to swim about but will also need rocks/ corals to provide some cover and to sleep in at night. As they are primarily herbivores they generally ignore invertebrates, but lush natural algae growth will be greatly appreciated. Once they get acclimated and become accustom to aquarium foods they are quite hardy and long lived.

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

Geographic Distribution
Naso unicornis
Data provided by
  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Actinopterygii
  • Order: Perciformes
  • Family: Acanthuridae
  • Genus: Naso
  • Species: unicornis
Bluespine Unicornfish, Naso unicornis
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School of Bluespine Unicornfish in the wild

This beautiful and very large Bluespine Unicornfish, while schooling in the wild, should only be kept one per tank. The exception to this would be a public aquarium with thousands of gallons! The blue colored spine earns this tang, unicornfish, or surgeonfish it's popular name, however many know this guy by the name Unicorn Tang. The name unicornfish is given for obvious reasons. Interestingly, the Naso Tang or Lipstick Tang does not grow a "horn" on the forehead, even though they are in the same genus! Catch your Bluespine Unicornfish with a container or bag, never a net! House in a tank that is 360 gallons or more.

Bluespine Unicornfish, Naso unicornis, feeding in public aquarium
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This video shows their very personable nature!

The Bluespine Unicornfish, like many of the tangs, develop a dog-like quality that endear themselves to aquarists. The Bluespine Unicornfish or Unicorn Tang, will grow to 27.5." Interestingly, all tangs in the genus of Naso tank will reach 80% of their full size within their first 5 years of life, meaning this tang will grow 4.4" per year! This emphasizes the need to put them in the minimum tank size of 360 gallons even while young. They do need an established tank, so the tank should be up and running and producing natural algae for them. They can hold their own with pretty much any other fish except the most aggressive triggerfish and possibly the Sohal Tang, who has a nasty reputation once full grown.

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Habitat: Natural geographic location:   The Bluespine Unicornfish or Unicorn Tang was described by Forsskål in 1775. They are found widespread throughout the Indo-Pacific from the Red Sea to Japan, the Rapa Islands, Hawaii, Tuamotu, and the Marquesas.
   In their natural habitat they are usually found at depths between 16 - 263 feet (5 - 80 meters) but have been reported as deep as 590 feet (180 meters) along outer reef walls. They rarely occur alone, rather they are usually seen in small (occasionally large) schools in shallow moving waters of inner and outer reefs and canals. Juveniles occur in groups close to the reefs. In Hawaii they are used as a food fish.

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

Description:    The Bluespine Unicornfish or Unicorn Tang has a deep elongated body shape with a narrower caudal peduncle, features that distinguish this genus from other Acanthurids. Adults have an olive to grayish body with blue hues, and yellowish tones on the belly. The dorsal and anal fins are thinly edged with blue and there is a light blue cast to the lips. The caudal fin develops elongated filaments or streamers. When these fish reach about five inches in length, they begin to develop a prominent rostral horn. This horn remains small, not extending any further than the end of the snout. Juveniles are a light greenish-gray color. The dorsal and anal fins are yellowish, thinly edged with a bright blue.
   Its name 'bluespine' is derived from the two fixed spines or "scalpels" surrounded by bright blue on each side of the caudal peduncle. 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 27.6 inches (70 cm).

Maintenance difficulty:    Once eating, Bluespine Unicornfish are quite hardy and 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. 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.
     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. Fortunately the skin on the Bluespine Unicornfish is very tough and they are not as likely to develop Marine Ich as many of the other species. Just the same, they 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 Bluespine Unicornfish or Unicorn Tang are primarily herbivores. In the wild they feed mainly on leafy brown algae like Sargassum and Dictyota. Provide lots of algae, large chunk types of prepared frozen formulas containing algae or spirulina, and flakes. Japanese Nori or other seaweed can be adhered to the aquarium glass with a vegetable clip. It will also feed on some frozen brine and mysis shrimp, mosquito larve, grindal worms, tubifex, and Enchytaeidae. Live rock with heavy algae growth will be greatly appreciated as it will allow this fish to constantly scrape with its rasping teeth. Culturing macro algae like chaetomorphia in the tank is also a great idea. Adults will eat zooplankton, shrimp, mysis and other cut up fish. Feed at least 3 times a day in smaller amounts instead of a large quantity once a day. This will keep the water quality higher over a longer time.
   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 large specimen that is constantly moving, it will spend a good deal of its time in the open water. 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 to provide some cover 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 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 (25 - 28° C) will serve them well.
Water Movement: Weak, Moderate, Strong
   All surgeonfish and tangs thrive with good water movement, need lots of oxygen, and love to have the water rushing over their gills. Provide strong movement in at least one area of the tank.
Water Region: Top, Middle, Bottom
   It will spend time in the open water constantly moving and grazing. 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 Bluespine Unicornfish is perhaps the most mellow of this group. 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.
   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:    The male of this species will have a better developed horn, stronger spines, and the caudal streamers will be more elongated.

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 Bluespine Unicornfish has not yet been bred in captivity, they have been observed pair spawning along the fringes of the feeding schools especially during the new and full moon. 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.Picture of a juvenile Bluespine Unicornfish or Unicorn Tang

Availability:    The Bluespine Unicornfish or Unicorn Tang is occasionally available. They are priced starting at around $30.00 USD and up.

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

Anna Baran - 2016-07-10
I am looking foe Bluespine Unicornfish

sam - 2009-08-24
I just got a unicorn tang and he seems to be settling in well. Still a bit stressed, but it has just been 2 days and the yellow tang is doing a bit of chasing. He is a nice fish and hope he settles in well.

Bryan - 2006-02-13
i have kept all kinds of marine fish for some time and have found the unicorn tang to be one of the best aquarium fish as they tend to change colour very noticably and rapidly to match their surroundings, but have also found them to be reasonably hard to keep as they do not like too much water fluctuation. a beautiful fish none the less.(males grow the spine on their head at a certain age and the tail elongates)

Anna Baran - 2016-07-10
I am looking foe Bluespine Unicornfish