The Bluespine Unicornfish can be pale grayish tan, gray or light greenish-gray while juveniles.  These tangs have a total of 4 sharp scalpel-like retractable blades at the base of their elongated caudal fin area.  Adults sport a variety of colors, depending on their location in the reef.  In the wild, while in the water column, they will take on a more blue-green to olive-green appearance to blend in with the open ocean, then will trade those colors to better match the substrate and rock work as they swim in lower levels. They have yellowish belly and yellow dorsal and anal fish with narrow blue stripes that almost glow.  The back of the tail fin is tipped in this blue coloring as well.  In captivity, most often the color they display will be a light bluish gray on the body area but they retain those bright blue accents.  Their eyes are surrounded in a goldish ring as they get older and the lips are light blue.  This fish will already have their 4 blue curved knife-like spines on the caudal peduncle, or the area right before the tail fin and they start forming the little “horn” while young around 4.7″ when the first bump on their forehead starts to appear.   The Unicorn Tang, as it is also referred to, will grow to 27.5,” with tangs growing to 80% of their total length within the first 4 to 5 years.  Tangs have a life span of 30 to 45 years (Choat and Axe 1996); however in captivity, it varies drastically. They are best left to intermediate aquarist who can handle the 360 gallon tank that they need. 

The Bluespine Unicornfish is one of the largest fish to be sold in the aquarium industry (over 2 feet in length).  Though this tang does grow a horn, there are several in the Naso genus that do not, thus adding to the countless names given to the different species in this genus.  Males can change the color in their horn, which is used during courtship of females and also as a signal to rival males!  Naso tangs will take on a very dark color when aggressive, a mottled gray and dark coloring when afraid or hiding, and males will color flash females during courtship.  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.

This fish is easy to care for as long as the tank is large enough, thus the challenge is the tank size.  They grow 4.4″ per year and by 5 years they will have reached 22″ in length.  This is 80% of their eventual 27.5,” so starting them out in a smaller tank is probably futile unless you are adding them to the main 360 gallon tank last and need 6 months to finish adding other fish first.  By 5″ they will need 180 gallons, just to give a rough idea of tank size.  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 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.   This makes them perfect in a community tank because they will get along with most other marine fish. This species has been known to get aggressive with other surgeonfish, especially those of its own genus. Unless you have a monster tank that is over 500 gallons, it is best to house just one Naso tang to a tank.  They get along with all fish except very aggressive triggers or predatory fish that can swallow them whole (as juveniles).  Assessors may be too timid due to their large size and swimming habits.  The Bluespine Unicornfish is primarily herbivorous they generally ignore invertebrates. Lush natural algae growth will be greatly appreciated and nicely suited for a reef environment.  A rare specimen may taste the slime that LPS and clams produce, however, this is only done by a hungry tang.  

   Like all surgeonfish and tangs, the Bluespine Unicornfish likes a lot of water turbulence rather than a placid aquarium.  A strong skimmer and good filtration is a must.  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.  To avoid illness and disorders, they will need vigorous filtration, protein skimming, and regular small water changes. 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. Once they get acclimated and become accustom to aquarium foods they are quite hardy and long lived.  Have a moderate light to grow algae and keep the water temperature steady anywhere between 72 and 78˚F.

Scientific Classification


Bluespine Unicornfish – Quick Aquarium Care

Aquarist Experience Level:Intermediate
Aquarium Hardiness:Very Hardy
Minimum Tank Size:360 gal (1,363 L)
Size of fish – inches27.5 inches (69.85 cm)
Temperature:72.0 to 78.0° F (22.2 to 25.6&deg C)
Range ph:8.1-8.4
Diet Type:Herbivore

Habitat: Distribution / Background

  The Bluespine Unicornfish, Naso unicornis, was described by Forsskål in 1775.  Their most common names are Bluespine Unicornfish, Bluespine Unicorn, Brown Unicornfish, Long-Snouted Unicornfish, Longnose Unicornfish, Surgeonfish, Unicorn Tang, and plain ol’ Unicornfish.  The name ‘bluespine’ is derived from the two fixed spines or “scalpels” surrounded by bright blue on each side of the caudal peduncle.  The term unicornfish has obviously something to do with the horn they grow!

   They are found widespread throughout the Indo-Pacific from the Red Sea to Japan, the Rapa Islands, Hawaii, Tuamotu, and the Marquesas.  They are found in moats, lagoons, seaward reefs with strong water movement and channels.  Juveniles are found in shallow waters of protected bays and harbors  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.  Blue Unicornfish prefer coarse, leafy, brown algae such as Sargassum, but will also eat  a wide variety of other brown algae and some zooplankton.  In Hawaii they are used as a food fish, however they have been known to cause poisoning to humans who consume them.

They are listed under the IUCN Red List of Threatened Species under Least Concern. 

  • Scientific Name: Naso unicornis
  • Social Grouping: Groups – In captivity, they should be one per tank.
  • IUCN Red List: LC – Least Concern


  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, however the male’s horn is slightly longer than the female’s and he can make the colors more intense during courtship.  Juveniles are a light greenish-gray color or grayish tan. The dorsal and anal fins are yellowish, thinly edged with a bright blue.  They have 6 spines on their dorsal fins, 2 spines on their anal fins, and 2 sharper and more prominent curved sharp spines in bright blue on each side of the the caudal fin area for a total of 4!  Naso tangs will grow to 80% of their body length in the first 4 to 5 years of life, at which time they will reach about 22″ in length.  The Bluespine Unicornfish will grow to 27.5″ and tangs in the Naso genus can live 30 to 45 years (Choat and Axe, 1996).  

  • Size of fish – inches: 27.5 inches (69.85 cm) – Reaches 22″ in the first 5 years of life.
  • Lifespan: 30 years – 30 to 45 years (Choat and Axe 1996), possibly less in captivity.(Choat and Axe, 1996)

Fish Keeping 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. Since they grow 4.4″ per year they need to 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.

  • Aquarium Hardiness: Very Hardy
  • Aquarist Experience Level: Intermediate – Due to large tank size needed to properly care for them.

Foods and Feeding

   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 larvae, 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.

  • Diet Type: Herbivore
  • Flake Food: Yes
  • Tablet / Pellet: Yes
  • Vegetable Food: Most of Diet – 90%
  • Meaty Food: Some of Diet – 10%
  • Feeding Frequency: Several feedings per day – Put algae sheets on clips in between feedings. Feed a variety of foods each day.

Aquarium Care

   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.

Reef tanks:
-Large Tanks 100 gallons and over, once water is aged and stable can be changed 10% bi-weekly to 20% monthly, depending on bioload.

Fish only tanks:*
-Large Tanks 100 gallons and over, once water is aged and stable can be changed 20% to 30% every 6 weeks depending on bioload.

For more information on maintaining a saltwater aquarium see: Saltwater Aquarium Basics: Maintenance. A reef tank will require specialized filtration and lighting equipment. Regular water changes done  bi-weekly will help replace the trace elements that the fish and corals use up.  

For more information see, Marine Aquarium Basics: Maintenance

  • Water Changes: Bi-weekly – Monthly for fish only tanks.

Aquarium Setup

   The Bluespine Unicornfish is one of the largest tangs kept in the marine hobby.  Reaching almost 28,” they need to be housed in a tank that is at least 360 gallons by the time they are 14” long, which they will reach by 3 to 3.5 years old.   In the meantime, up to 4 or 5” long they can be kept in a 100 gallon tank, then in a year, once they are 8 to 9” long, a 180 gallon tank and by 3 years, they will be 11 to 13” long and ready to enter into their new 360 gallon tanks within the next few months.   Too small of an environment can stunt their growth and they can develop ‘behavior problems’. 

   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. Have enough light to provide algae growth.  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.  The best temperatures to keep them are between 72 – 78° F; keeping in mind that the lower the temperature the more oxygen they will have.  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.  Your Unicorn Tang will spend time in the open water constantly moving and grazing.  It will sleep in crevices at night, so make sure your “crevices” grow with your pet.

  • Minimum Tank Size: 360 gal (1,363 L) – 4-5″ – 100 gallons 6-9″ – 180 gallons 10-14″ – 250 gallons 14″ – 360 gallons
  • Suitable for Nano Tank: No
  • Live Rock Requirement: Typical Plus Hiding Places – Provide large enough crevices for them as they grow.
  • Substrate Type: Any
  • Lighting Needs: Moderate – normal lighting – Enough to provide algae growth.
  • Temperature: 72.0 to 78.0° F (22.2 to 25.6&deg C)
  • Breeding Temperature: – unknown
  • Specific gravity: 1.023-1.025 SG
  • Range ph: 8.1-8.4
  • Brackish: No
  • Water Movement: Strong
  • Water Region: All

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.   However unless you have a huge (500 gallons plus) system, it is best to house just one Naso tang to a tank.

   They get along with most other marine fish and can be kept with a variety of tank mates including other genus’ of surgeonfish in larger tanks. 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.  When it comes to other fish, Assessors may feel too threatened by such a large fish and may wither away as it “hides to death.”  A large grouper can eat a smaller tang, so avoid housing them together unless the tang stays larger than the grouper at all stages of BOTH fish’s life spans.  Toadfish will also try to eat them!  Avoid pipefish, seahorses and frogfish since they are best kept separately in their own tanks. 

Although literature states that a rouge tang will nip at large-polyp stony corals, most aquarists to feed their tang properly will not run into this problem.  Don’t confuse picking at corals with them picking at any algae at the base of a stony coral, which was a great service to the coral!

Inverts are not at risk, however a copepod or amphipod may be eaten here or there while the tang grazes on the algae in which they live.  On a rare occasion, an occasional tang will find the slime that clams produce quite tasty.  While the tang is not biting the clam, the action causes the clam to close often, stressing the clam and eventually this stress will kill the clam.  This shouldn’t be a problem with a well fed tang.

  • Venomous: No
  • Temperament: Semi-aggressive – Peaceful to non-tangs.
  • Compatible with:
    • Same species – conspecifics: No
    • Peaceful fish (gobies, dartfish, assessors, fairy wrasses): Safe – Assessors will be too intimidated and will not come out.
    • Semi-Aggressive (anthias, clownfish, dwarf angels): Safe
    • Safe
    • Large Semi-Aggressive (tangs, large angels, large wrasses): Monitor – Only house with different genus of tangs that are different colors and shapes and in larger tanks.
    • Large Aggressive, Predatory (lionfish, groupers, soapfish): Monitor – As long as they are larger than all of these fish, including frogfish and toadfish. Avoid aggressive triggerfish.
    • Monitor – Mandarins will be fine, however frogfish, pipefish and seahorses should be kept in their own tank.
    • Anemones: Safe
    • Mushroom Anemones – Corallimorphs: Safe
    • LPS corals: Monitor – Should not bother LPS if well fed.
    • SPS corals: Safe
    • Gorgonians, Sea Fans: Safe
    • Leather Corals: Safe
    • Soft Corals (xenias, tree corals): Safe
    • Star Polyps, Organ Pipe Coral: Safe
    • Zoanthids – Button Polyps, Sea Mats: Safe
    • Sponges, Tunicates: Safe
    • Shrimps, Crabs, Snails: Safe
    • Starfish: Safe
    • Feather Dusters, Bristle Worms, Flatworms: Safe
    • Clams, Scallops, Oysters: Monitor
    • Copepods, Amphipods, Mini Brittle Stars: Safe

Sexual differences

Like others in the Naso genus, males are larger, have a more pronounced caudal peduncle (thick area before the tail fin where the scalpel is located), have long streamers from the top and bottom of the ends of their tail fins, and the horn on their forehead will be longer. 

Breeding / Reproduction

Males will flash their coloring while courting females, producing an intense color throughout the body.  They also change the color of their horn during displays between females and rival males.

   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.

  • Ease of Breeding: Unknown – A very RARE tang will find the slime clams produce yummy, causing the clam to close and stress.

Fish Diseases

Tangs produce less body slime than other saltwater fish and have been termed “dry skinned” fish by some.  This makes them very susceptible to Cryptocaryon (saltwater ich), Marine Velvet and other diseases.  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.  The most common ailments are bacterial diseases, Hole-in-the-Head Disease or Lateral Line Disease, and parasitic infections such as protozoas, worms, etc.  

They are definitely a candidate for quarantine when you first receive them, with a stress-free environment (no other fish), good quality veggie foods, places to hide and a quiet area for the aquarium.  . 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.   To avoid Lateral Line Diseae, avoid using activated carbon, as it has been linked to this disorder.  Providing vitamin C soaked foods and good quality macro algae and greens will also help reversea and prevent it.   

For more information see Fish diseases.


The Bluespine Unicornfish is a seasonal fish.  Babies, under 3,” start at $34.99 and adults, 9 to 12,” will set you back around $350.00  (2014)



Featured Image Credit: chonlasub woravichan, Shutterstock