Most often the Chocolate Tang or Mimic Tang is available as a juvenile, and depending upon where it was collected, will look very much like the dwarf angelfish also living in that location. As this tang gets older it changes into its very pretty adult coloration shown in the picture above.

   The Chocolate Tang or Mimic Tang is a good choice for the home aquarium. They go through an interesting color change from juvenile to adult and are favored because they don’t get as large as many others in the same genus. They are moderately easy to care for as long as they are provided with a good environment and their nutritional needs are met.

   Like all surgeonfish and tangs, the Chocolate Tang likes lots of water turbulence rather than a placid aquarium. It can be kept in a fish-only tank as long as there is plenty of swimming room and plenty of rocks/ corals with nooks and crannies to hide in. It is not too picky about foods once it gets settled, and like most surgeonfish this can be accomplished by initially offering a good macro algae. Gracillaria works well as most tangs can’t resist it. Though they can be kept with a variety of tank mates, they will be aggressive towards others of their own kind. They may also fight with other surgeonfish or tangs, especially new additions to their aquarium.

Scientific Classification


Habitat: Natural geographic location:

  The Chocolate Tang or Mimic Tang was described by Kittlitz in 1834. They are found in the Indo-Pacific from Seychelles to Japan, the Community Islands, the Marquesas and Tuamotu. It co-occurs with its close relative the Indian Ocean Mimic SurgeonfishAcanthurus tristis in Bali.
   As adults they are generally found singly inhabiting shallow lagoons and coastal reef slopes and crests, enjoying areas with corals, rock and sand at the base of reefs. They are found at depths between 13 to 196 feet (4 – 60 meters).
   Tiny Acanthurus are initially quite wary, hiding in crevices among rubble and rocks. But soon the need for feeding draws them into small mixed groups where they seek the protection of numbers. The behavior of the Mimic Tang is similar, however as the juveniles are excellent mimics of dwarf angelfish, they are often seen in their company. Beyond just protection, research has suggested another interesting purpose for this mimicry is to provide a way for this young surgeonfish to feed. Basically surgeonfish have a much more restricted diet than that of the angelfish, and one that is very similar to damselfish. Thus the damselfish will attack the surgeonfish unrelentingly, while the angelfish feed with fewer attacks. This mimicry deceives the damselfish so the mimic will suffer fewer attacks from the damselfish, allowing it to feed more freely.


   These fish are not listed on the IUCN Red List.


   An adult Chocolate Tang or Mimic Tang is very similar looking to other Acanthurus species as far as size and facial features. They have a disk like shaped body with a spine that is like a scalpel on either side of the caudal peduncle. The adult has a yellow to dark brown or purplish black body with an orange patch just above the pectoral fin base. There is a broad dark band starting at the top of the gill opening and arcing down to below the chin and there is a narrow white band encircling the chin. On the end of the caudal fin is a broad yellow band.
   As juveniles they are ‘mimics’ and will imitate such pygmy angelfish as Eibl’s AngelfishCentropyge eiblii, Lemonpeel AngelC. flavissimus, Herald’s AngelfishC. heraldi, or Pearlscale Angelfish C. vrolikii. Their juvenile colors will look like that of the angelfish they are imitating. For example when mimicking the Eibl’s Angelfish, the juvenile has a cream colored body with vertical orange stripes and a black tail. When mimicking the Herald’s Angelfish it will be all yellow, and as a Lemonpeel Angel it will be all yellow with a blue ring around the eye and blue edging along the margins of the fins. Looking like a Pearlscale Angelfish it will have a body that is light towards the front, getting very dark on the back third and on the fins, with grayish spotting.
   There are some possible explanations given for this mimicry. One idea is that it provides protection while their caudal peduncle spine is immature. The small pygmy angelfish being copied are rarely preyed on; hence, the convenience of being misunderstood is a good thing for the young mimic. The other idea is that this mimicry will deceive damselfish as to their diet, giving them access to food supplies in the damselfish’s defended areas.

Length/Diameter of fish

   Adults reach 9.8 inches (25 cm).

Maintenance difficulty

   The relatively small size of the Chocolate Tang lends itself to being a great addition to the marine aquarium. It is easy to acclimate and keep if you purchase a juvenile, adults are reportedly very hard to acclimate. Once it is use to its environment it is quite hardy, adaptable to a wide variety of foods, and can handle a wide range of water parameters. However, it will do best in an environment that provides consistency, not only in water conditions and quality, but also in decor and fellow inhabitants. It can be housed in a fish-only tank or in a reef environment as it will not harm corals or invertebrates.
   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 plenty of space, especially for adult specimens, along with lots of rocks/ corals with crevices for retreating and for sleeping. This decor will also lend itself to algae growth which surgeonfish enjoy grazing on, making them a valuable addition to a reef environment.
   Surgeonfish and 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 Chocolate Tang is very tough and is 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. 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.


   The Chocolate Tang or Mimic Tang are primarily herbivores. In the wild they graze on benthic algae. In the aquarium the majority of their intake will be vegetable matter, but they do need some meaty foods as well. Provide lots of algae, prepared frozen formulas containing algae or spirulina, frozen brine and mysis shrimp, and flake foods. Japanese Nori or other seaweed can be adhered to the aquarium glass with a vegetable clip. 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 three 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.


   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. 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

   All surgeonfish/ tangs are quick agile swimmers and need lots of open areas. To feel secure they also need rocks/ corals with many nooks and crannies to hide in and to wedge themselves into at night for sleeping. This fish will not bother corals or inverts but it will graze on algae, so it highly useful in a reef environment.
Minimum Tank Length/Size:
   A minimum 75 gallon (284 liters).
Light: Recommended light levels
   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 78 -82° F (26 – 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 at times. Provide strong movement in at least one area of the tank.
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 the Chocolate Tang is that they are fine in a reef setting with inverts and corals, and they will graze on the algae. They can also be kept in a fish only aquarium and their personality is not overly aggressive with most tank mates. Several juveniles can be kept together for a while, but become incompatible as they get older, so are best kept singly. They can handle themselves just fine with more aggressive fish like triggers, large wrasses, and puffers.
   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 Naso Tang, Yellow Tang, and a Hippo Tang with out 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.

Sexual differences

   No sexual difference is noted for this species.


   The Chocolate Tang or Mimic Tang has not yet been bred in captivity. 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.
   For information on breeding and the development of the fry, see: Marine Fish Breeding: Tangs.


  The Chocolate Tang or Mimic Surgeonfish is regularly available at retailers. They are priced around $45.00 USD and up.

Featured Image Credit: Chayanon Chewkit, Shutterstock