Though still quite rare, the Elongate Unicornfish or Lopez’s Unicornfish is becoming a bit more common in pet stores. The fish seen in the picture above has been keep for over six years!

The Elongate Unicornfish is elongated, thus the name, in comparison to other tangs.  They are iridescent grayish-blue on the top part of the body, fading to a white belly.  They have closely spaced black spots on the upper half of their body and tail.  Although the have the name “Unicornfish,” this unicorn is hornless!  They grow to up to about 24″ and can live to 30 to 45 years (Choat and Axe, 1996).  This large tang is best left to intermediate aquarists due to tank size.

The Elongate Unicornfish, like most Naso tangs are very personable pet fish.  Once it is comfortable it can even be trained to accept foods from its keeper’s hand.  They look very similar to the Vlamingi Tang (Naso Vlamingii) when juveniles.  When angry, about to fight or fighting, all Naso tangs turn completely dark.  When frightened or sleeping, they will hide and turn a mix of gray and dark, yet when being cleaned by a cleaner wrasse, they will lighten to a silver gray.  Lastly, this genus tend to have blue hues in the water column in the wild and change their coloring to better match the rock and substrate  when they are in lower levels of the reef.  

Provide your initially shy Elongate Unicornfish with lots of room to roam around in and some live rock with naturally growing algae and mysis, and chopped table shrimp to entice it to eat. Once eating, your little guy can be offered a variety of algae based aquarium fare for its basic diet, along with meaty foods from the mollusk family (saltwater varieties).  Once they get acclimated and become accustom to aquarium foods they are quite hardy and long lived.  Tanks that are smaller can cause behavioral problems as they become adults.  They will be almost 19″ by the time they are 5 years old, indicating a growth of 3.5 to 4″ per year.  They are quite hardy once acclimated to their home. 

Being a peaceful fish with an amicable nature, it will get along with most other marine fish, except others from their genus.  Unless you have a huge (hundreds of gallons) system, it is best to house just one tang to a tank.  You can add other tangs that are from a different genus in a tank that is very large, however do this when they are young and all at the same time.  They get along with all fish except very aggressive triggers or fish that can swallow them whole (as juveniles).  Assessors may be too timid due to their large size and swimming habits.  Natural algae growth and lots of little meaty living morsels like copepods and amphipods will be greatly appreciated!  They are nice suited for a reef environment if the corals are glued down due to their bursts of “I just have to be OVER THERE right NOW!!”  Stomenella and other very small snails that are 1/2” or less may be eaten.   A rare specimen may taste the slime that LPS and clams produce, however, this is only done by a hungry tang.

Tank size should be 180 gallons or more.  The Elongate Unicornfish likes a lot of water turbulence rather than a placid aquarium with open areas above coral and rock to swim as they will pace back and forth during the day. They also need rocks/corals to provide some cover and to sleep in at night.  Be sure to provide larger crevices for them to sleep in as they get older.  The lower end of their spectrum of temperature will have more oxygen, which is necessary for this active swimmer.  Tangs love to swim toward power heads to get that water “rush,” so provide at least one area in the tank that they can do this.  The back of the tank is best suited if you have corals and don’t want them blown all over the place.  They will occupy all areas of the tank and it is possible, similar to the Naso Tangs, they may jump, so egg crate that is weighted down, especially once full grown is suggested. 

Scientific Classification

Species: lopezi

Elongate Unicornfish – Quick Aquarium Care

Aquarist Experience Level:Intermediate
Aquarium Hardiness:Moderately hardy
Minimum Tank Size:180 gal (681 L)
Size of fish – inches:23.6 inches (59.94 cm)
Temperature:72.0 to 76.0° F (22.2 to 24.4&deg C)
Range ph:8.1-8.4
Diet Type: Omnivore
Elongate Unicornfish and cleaner wrasses
Image Credit: SeraphP, Shutterstock

Habitat: Distribution / Background

The Elongate Unicornfish, Naso lopez, was described by Herre in 1927.  The names most often associated with this fish are Elongate Unicornfish, Lopez’ Unicornfish, Slender Unicorn, Surgeonfish, and Unicornfish, although they will not grow a horn.


They are found widespread throughout the Western Pacific; southern Honshu, Japan to the Great Barrier Reef and New Caledonia, Similan Islands in the Andaman Sea and Guam, and recently from Tonga.

In their natural habitat they are usually found at depths between 65 – 164 feet (20 – 50 meters) but have been reported as deep as 98 feet (30 meters). They inhabit coastal to outer reef slopes with strong currents and feed on mollusks (Cavolinia uncinata) which only grow to 1/2” or 15 mm, weeds, algae, amphipods, small crabs, diatoms, phytoplankton, stomatopods and copepods.  They occur singly, in small groups, and occasionally form large schools. They are on the IUCN Red List under Least Concern. 

  • Scientific Name: Naso lopezi
  • Social Grouping: Varies – Can be found solitary, in pairs or in groups
  • IUCN Red List: LC – Least Concern


The Elongate Unicornfish or Lopez’s Unicornfish, as its common name indicates is quite slender. Like the other Naso species, this elongated body shape and a narrow caudal peduncle are features that distinguish this genus from other Acanthurids. Though it is a ‘unicornfish’, neither the male nor the female will grow a horn.

Adults generally have an iridescent grayish-blue body color that becomes paler on the lower half. The upper half of the body and head have numerous small round dark spots. Like all of the unicornfish it has the ability to quickly and dramatically change its color from pale to brilliant to dark, depending on mood or environment. The body can be nearly black, sometimes a dark violet, or a pearl gray. The spots can be turquoise to dark gray and the head can have some yellows. The eye is edged in turquoise.  Like all Naso species, they have the ability to quickly and dramatically change, depending on mood or environment. When excited or hiding in the reef their body can become almost black with gray splotchy patches.  When angry, becoming aggressive and fighting they turn completely dark, and when being cleaned by cleaner fish, they turn completely pale to allow cleaner wrasses do to a more thorough job at cleaning them.  The tangs in this genus have been observed changing coloring to match the color of the substrate or rock work they are near.  While in the open water, they have more blue hues and will switch to colors that are better suited to match the substrate.

On each side of the caudal peduncle are two fixed spines or “scalpels” used for defense or dominance.  They have 5 spines on the dorsal fin, one spine on the pelvic fin and 2 spines blades on the caudal fin area, or the area right before the actual tail fin.  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.

The Elongate Unicornfish has been reported to grow up to 23.6” (60 cm).  Since tangs grow up to 80% of their total length within the first 4 to 5 years, they will reach almost 19” by then if they are males since females are smaller.  Tangs have a life span of 30 to 45 years (Choat and Axe 1996), yet in the wild, it may take less time to reach this size. 

 NOTE:  At first we wondered if the photo above really is an Elongate Unicornfish, due to the similarity of this fish to the juvenile form of the Vlamingi Tang N. vlamingii. However there are definite distinctions and it does match the description that we found in Fishes of the Great Barrier Reef and Coral Sea, Revised edition, by John E. Randall, Gerald R. Allen and Roger C. Steene. There is also a very similar photo representation in Dr. Burgess’s Atlas of Marine Aquarium Fishes, by Dr. Warren E. Burgess, Dr. Herbert R. Axelrod, and Raymond E Hunziker III.

Juvenile Elongate Unicornfish have a more bluish gray coloring and lack the blue speckling on the base of the tail fin that the Vlamingi Tang juvenile has.  The Vlamingi Tang will form a “hump” or very blunt section where a “horn” would be, however the Elongate Unicornfish is sleek and a more slender fish. 

  • Size of fish – inches: 23.6 inches (59.94 cm) – 60 cm – Females smaller
  • Lifespan: 30 years – 30 to 45 years (Choat and Axe 1996), possibly less in captivity.

Fish Keeping Difficulty

Once eating, Elongate Unicornfish are 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 3 – 4″ per year. They must be housed in a 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.  A healthy Elongate 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.

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.

  • Aquarium Hardiness: Moderately hardy – As long as the tank is large enough.
  • Aquarist Experience Level: Intermediate – Due to large tank size needed.
Elongate Unicornfish
Elongate unicornfish in Night coloration (Naso lopezi) (Image Credit: Rickard Zerpe, Wikimedia Commons CC BY-SA 2.0 Generic)

Foods and Feeding

   The Elongate Unicornfish in the wild will eat mollusks (made up majority of their diet), algae, weeds and zooplankton, making them closer to an omnivore than an herbivore.  Provide lots of algae, raw shrimp, mysis, large chunk types of prepared frozen formulas containing algae or spirulina, freeze dried plankton, 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. An occasional live rock with micro and macro organisms will be greatly appreciated. Culturing macro algae like chaetomorphia in the tank is also a great idea. Feed at least 2 – 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: Omnivore – Eats various mollusks and algae.
  • Flake Food: Yes – Flake with spirulina added.
  • Tablet / Pellet: Yes – Flake with spirulina added.
  • Live foods (fishes, shrimps, worms): Some of Diet – As a treat or to help them adjust.
  • Vegetable Food: Most of Diet – Best foods are macro algae, algae sheets, Nori and spirulina based foods.
  • Meaty Food: Some of Diet – They do need some meaty foods like mollusk meat, mysis and fortified brine shrimp.
  • Feeding Frequency: Several feedings per day – Hang an algae sheet or Nori in the tank in between feedings.

Aquarium Care

   An Elongate Unicornfish is very active and 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.

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.  

*Note:  If this is the ONLY fish in the tank, with no corals or other fish you can get away 20% monthly.

For more information see, Marine Aquarium Basics: Maintenance

  • Water Changes: Bi-weekly

Aquarium Setup

   A minimum tank size of 180 gallons (with a minimum length of 6 feet), is needed by the time this tang is 4 to 5″ which is usually the purchase size.  They grow about 3″ a year in their first 5 years, reaching over 14″ by the time they are 5 years old.   Keeping them in a smaller tank will mean having to move them within a year.  If your Elongate Unicornfish is only 2″ to 3″ then a 75 gallon tank will be fine for about 6 months to a year.  If the tank is too small, this can stunt their growth, causing health issues along with development of ‘behavior problems’.  Provide an open area on the top part of the tank with no rocks and below add plenty 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, along with the copepods and amphipods they like to eat.  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.  

     They can handle a wide range of water parameters but will do best in an environment that provides consistency, not only in water conditions and quality, but also in decor and fellow inhabitants.  With that in mind temperatures should be temperatures need to be kept stable and somewhere between 72 – 79° F (23 – 26° C) and pH between 8.1 to 8.4.  All surgeonfish need an aquarium with plenty of aeration and a strong current that they will face into since they love to have water rushing over their gills!  This will help to provide good oxygenation which they need due to their active swimming habits.  They are found at all levels of the tank, and will spend time in the open water constantly moving and grazing.   Tanks will sleep in crevices or caves by spreading their fins and “locking” themselves in at night.

  • Minimum Tank Size: 180 gal (681 L) – Starting them out in this size tank is the best choice since they grow so fast.
  • Suitable for Nano Tank: No
  • Live Rock Requirement: Typical Plus Hiding Places – Provide crevices and caves slightly bigger than they are so they can wedge themselves in at night.
  • Substrate Type: Any
  • Lighting Needs: Moderate – normal lighting – Enough to grow natural algae.
  • Temperature: 72.0 to 76.0° F (22.2 to 24.4&deg C) – Tangs require more oxygen than other fish, and lower temperatures provide this need.
  • Breeding Temperature: – unknown
  • Specific gravity: 1.023-1.025 SG
  • Range ph: 8.1-8.4
  • Brackish: No
  • Water Movement: Strong – Tangs like to face linear power heads to increase oxygen dosage!
  • Water Region: All
Elongate Unicornfish underwater
Image Credit: SeraphP, Shutterstock

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 Elongate Unicornfish get along with most other marine fish and can be kept with a variety of tank mates and they are peaceful towards all but other tangs. 

   As far as housing them with other tangs, unless you have a huge (hundreds of gallons) system, it is best to house just one tang to a tank. They can be territorial especially with their own genus. This is why adding tangs that are different colors and genus is best done when everyone is young and all at the same time it a tank that is hundreds of gallons.  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. Introducing a new surgeonfish into an aquarium that already houses one or more is usually a problem. If it must be done, then change the rock work around to alleviate any aggression to the “new guy,” since they will be busy reestablishing territories, not defending their own.   A little chasing will occur, and while it usually doesn’t end up in a knock down drag out fight, still keep an eye on the new guy for at least a month.  Avoid housing with the more peaceful tangs.

  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! large energetic fish and may topple corals while swimming about in fast clips.  

   A few inverts may be at risk, including small snails like stomenella snails and other snails .5” or less, because they eat small snails in the wild.  They will eat copepods and amphipods, but they will not decimate the population.  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, but since this tang is fine with eating some meaty foods, keep an eye on your clams.

  • Venomous: No
  • Temperament: Semi-aggressive – Peaceful toward non-tangs.
  • Compatible with:
    • Same species – conspecifics: No
    • Peaceful fish (gobies, dartfish, assessors, fairy wrasses): Monitor – Assessors will be too intimidated and will not come out. Some peaceful fish may be picked on in inappropriately small tanks.
    • 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. They will be aggressive towards more peaceful tangs.
    • Large Aggressive, Predatory (lionfish, groupers, soapfish): Monitor – As long as the juvenile tang is larger than all of these fish, including large frogfish. Toadfish will attempt to eat them. 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: Monitor – Snails under and around 1/2″ or 16 mm may be eaten since they eat this sized snail in the wild.
    • Starfish: Safe
    • Feather Dusters, Bristle Worms, Flatworms: Safe
    • Clams, Scallops, Oysters: – Sometimes a tang will find the slime clams produce yummy, causing the clam to close and stress.
    • Copepods, Amphipods, Mini Brittle Stars: Safe – Will eat copepods and amphipods but will not decimate the population.

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. 

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 Elongate 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.

  • Ease of Breeding: Difficult

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) and other diseases.  The most common ailments are bacterial diseases, Hole-in-the-Head Disease or Lateral Line Disease, and parasitic infections such as protozoas (including Cryptocaryon), worms, etc.  

   As for treatment, some tangs are sensitive to copper.  To avoid Lateral Line Diseae, avoid using activated carbon, as it has been scientifically linked to those diseases.  The best routine is a quarantine tank and a stress free environment with good quality veggie foods, places to hide and a quiet area for the aquarium.


Though still quite rare, the Elongate Unicornfish or Lopez’s Unicornfish is becoming a bit more common in at retailers. They are occasionally available on the internet and are priced at about $70.00 USD and up.

Popular Searches



Featured Image Credit: SeraphP, Shutterstock