News / Species Spotlight / The Achilles Tang (09/03/15)

The Achilles Tang



by Charles J. Hanley III

Scientific Name: Acanthurus achilles
Common Name: Achilles Tang, Achilles Surgeonfish, Redspot Tang, Redspot Surgeonfish, Redtail Surgeonfish

Taxonomy:

Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Perciformes
Family: Acanthuridae
Genus: Acanthurus
Species: Acanthurus achilles

Description:

The newest entry into the annals of Species Spotlight is a little orange and black fish called the Achilles Tang (Acanthurus achilles; synonymous with A. aterrimus). These fish are scrappy and they flash their colors with pride! The Achilles tang is a challenging community fish, but does well in reef tanks and with fishes that do not look like other tangs.

Though the overwhelming aesthetic impression the Achilles gives is one of black and orange, looking more closely uncovers other colors as well. The dark body is black or dark chocolate brown, but may look bluish in certain lights. The caudal peduncle on each side has a bright orange teardrop, with the point aimed toward the tail. Singular dorsal and anal fins have dorso-ventral bands of white, orange, black, and white, moving proximally to distally. Finally, the caudal fin bears a distinguished crescent of orange, but ends with narrow vertical black and white bands. Achilles tangs also have black pectoral fins, and small white, orange, and black pelvic fins. The edge of the operculum is rimmed in white, and sometimes blue.

Achilles tangs have a typical tang-shaped body. That is, they are tall but laterally compressed, with an oblong profile. Maximum length is about 9 inches, but 7 inches is a more realistic maximum in an aquarium setting. The eyes are high up on the forehead, and the small mouth is low and inferior (down-turned). In fish, this perch-like body shape trades flat-out speed for agility, making the Achilles tang a nimble addition to a marine aquarium.

In general, one of the most interesting and problematic aspects of keeping tangs is that they have a sharp scalpel spine on either side of their caudal peduncles. In fact, this spine is the reason that many tangs are also called surgeonfish. These blade-like projections can be extended or folded away in a fleshy groove. The spine is used as a means of defense, and has been known to injure both aquarium fish and aquarium-keepers alike! On the Achilles tang, this spine is located on the narrow neck of the orange teardrop on either side of the caudal peduncle. Conscientious aquarists must take care to ensure that this spine does not damage their hands, other livestock, or get caught in a net where it can cause injury to the Achilles itself.


Ecology:

The common range for Achilles tangs includes the Hawaiian and Caroline Islands, and extends southwest to Northern Australia and Papua New Guinea. They are also occasionally seen as far east as the southern tip of Baja California, Mexico. In spite of this, the Achilles Tangs is primarily a central and western pacific fish species.

They are typically found in the shallows near forereef crests. Their agile body shape lends itself to this type of environment, as they can turn and react quickly to changes in currents and wave conditions. The shallowest waters also tend to have algal crests, where these fish can readily access their herbivorous food supplies. Though they may have some generalist tendencies, especially early in life, Achilles tangs are primarily algal eaters. Herbivory is common on coral reefs, though the difficulty in processing and digesting plant-like materials means that herbivores must spend a lot of time feeding. They tend to spend much of the day searching the surfaces and crevices of rocks, nibbling on morsels of algae.

Achilles Tangs, like many other tangs/surgeonfish, are somewhat moody. Okay, they are downright aggressive, having very little tolerance for fish that look like tangs, especially conspecifics. In the wild, as in the aquarium, they can be territorial and surly though adults may school together and graze as a unit (a wild behavior sometimes mimicked in the largest aquariums. In this manner, it is easier for them to enter the territories of other fishes and graze without harassment. When alone in an aquarium, an achilles tang may choose to become territorial and defensive. On other occasions, it may opt to coexist peacefully with other tangs.

In captivity, breeding is rare or non-existent. This could be a function of poorly-understood mating behaviors and needs, or simply a result of the intolerance of these fish for conspecifics. As a result, wild specimens are the only ones available, which has led to over-collection in certain areas, including Hawaii. Interestingly, the achilles tang is know to hybridize with another tang species, the Goldrim or Whitecheek tang (A. nigricans). The hybrid specimens fetch top dollar whenever they pop up for sale somewhere.


Aquarium Care:

There are really three main considerations when adding any new fish to an aquarium: 1) does it fit in well with the space and the community that are already there; 2) can it be kept well-fed; and 3) is it susceptible to disease or parasites? All three are valid questions to ask before getting an achilles tang. Because they have a justifiable reputation for being difficult, only experienced aquarists should attempt to keep achilles tangs, and only if they are well-informed about their needs.

The primary consideration must really be whether the tang will get along with your other fish. Tangs, and fishes of similar size and body shape, may become targets of an achilles aggression. This general behavioral pattern is characteristic of many tangs and surgeonfish, and the other competitors may turn the table on the achilles and come to dominate it. Either way, such situations are undesirable. There are many anecdotal reports that suggest that it is often possible to care for multiple tangs and surgeonfish in one tank, but these authors all report the common theme of having very large tanksusually between 175 and 200 gallons. The smaller the tank, the more likely conflicts become. To be safe, try to go with more small species, such as gobies, dottybacks, and damselfish, which may be ignored altogether in a large tank (100+ gallons). Achilles tangs are also considered reef-safe, though occasional coral nipping has been reported. The coral nipping is more indicative of individual taste than a proclivity that characterizes the species.

To some degree, the achilles tang is a generalist, though its primary diet is herbivorous in nature. In the wild, it feeds on macroalgae it picks off of the reefs surface. In doing so, it likely also acquires nutrition from small crustaceans that are unfortunate enough to be on the algae at the time. Juvenile tangs may feed on small copepods and decapods, as well as algae. Later in life, there is a shift towards herbivory. In an aquarium setting, it can be quite difficult to entice an achilles tang to begin eating. As usual, I recommend buying a specimen only after it has been kept successfully for several weeks by your local fish store. You should also ask to see it eat. Many foods have been recommended as appropriate for tangs and surgeonfish, including algal wafers, nori sheets, mysid and brine shrimp, broccoli heads, zucchini chunks, and leaf lettuce. It should be noted that leaf lettuce is not recommended as fish food, primarily because much of it is of low nutritional value. Fish also find it difficult to digest lettuce because they are not adapted to eat terrestrial plants. By this logic, they should be unable to digest broccoli or zucchini, yet these foods do not seem to garner the same objections. Nevertheless, it seems prudent to try and stick to marine based foods, such as algae wafers and pellets that contain Spirulina. Sheets of nori seaweed are also a good bet, as well as fortified brine and mysid shrimp. I also like frozen algae cubes, which usually contain some fish-based proteins and lipids along with diverse forms of algae. Variety is always good, especially when a fish is first introduced. Feed a new achilles any kind of quality aquarium food it is willing to eat, at least until it eats willingly. Once it is comfortable enough to feed, you can begin weaning it onto a more tang-specific diet.

Diet will affect an aquarists ability to control disease, though quarantine should be the very first line of defense. As a group, tangs are particularly susceptible to afflictions and ectoparasites such as Head and Lateral Line Erosion (HLLE), marine ich (Cryptocaryon irritans), and tang turbellarian or black ich disease (caused by parasitic flatworms). Since they are so sensitive to disease, they may be carriers that introduce pathogens into your system. They may also fall victim to problems that are already present. It is important to quarantine any new fish for several weeks before adding it to a display system. Treatment, if needed, is far easier to achieve if the fish is all alone in an empty tank. Once introduced into a community, possible treatments will likely be limited to medicated foods (which may or may not be eaten) and system wide dosing (which will not be possible reef tanks). Feeding a healthy diet with a lot of variety that is fortified with vitamins and Omega-3 fatty acids, along with occasional offerings of garlic-laced foods, will help keep an achilles tang happy. Additionally, maintaining exceptionally clean water is essential for keeping these ammonia-sensitive fish alive. Because they are grazers by nature, feeding 3-4 times daily is another necessity. Accordingly, heavy filtration, strong currents, and powerful protein skimming are musts.





Works Cited:

Anonymous. Achilles Tang. Aquarium Passion Online. 2008. URL: < http://www.aquariumpassion.com/profiles/saltwater-fish/acanthuridae/achilles-tang.html >

Brandt, J. The Blue Tang. Quality Marine Online. 2009. URL: < http://www.qualitymarine.com/News/Species-Spotlight/The-Blue-Tang-%2802/11/09%29 >

Froese, R. Acanthurus achilles, Shaw, 1803, Achilles Tang. Fishbase.org. 2010. URL: < http://fishbase.org/Summary/SpeciesSummary.php?ID=4306&genusname=Acanthurus&speciesname=achilles >

Goemans, B. and L. Ichinotsubo. The Marine Fish Health and Feeding Handbook; The Essential Guide to Keeping Saltwater Species Alive and Thriving. TFH Publications: Neptune City. 2008.

Hauter, S. and Debbie Hauter. Achilles Tang Profile. About Online. Undated. URL: < http://saltaquarium.about.com/od/tangsurgeonfishprofiles/p/achillestang.htm >

ITIS Report. Acanthurus achilles, Shaw, 1803. ITIS Report. 2010. URL: < http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=172261 >

Jennings, G. The New Encyclopedia of the Saltwater Aquarium. Buffalo: Firefly books Ltd., 2007.

Lieske, E. and R. Meyers. Coral Reef Fishes, Revised Edition. Princeton University Press: Princeton, 2001.

Mondadori, A. (ed.). Simon & Schusters Guide to Freshwater and Marine Aquarium Fishes. Fireside: New York. 1977.

Siegel, T. Secrets of the Achilles Tang. Fishchannel Online. 2007. URL: < http://www.fishchannel.com/saltwater-aquariums/aquarium-frontiers/finding-the-achilles-secret.aspx >

Veaila, R. Achilles Tang: A Guide on This Highly Prized Surgeonfish. Undated. Pet Memorial Urns Online. URL: < http://www.pet-memorial-urns-online.com/achilles-tang-a-guide-on-this-highly-prized-surgeonfish/ >