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Acanthurus mata

 Click on the photo to see the high resolution image. Photo taken at "Water Inn" petshop by G.J.Reclos /MCH - Jan. 2006

How many Surgeonfishes in the genus Acanthurus do you know? There are Powder Browns (A. nigricans (nee glaucopareius) and A. japonicus), the Powder Blue, Atlantic Blue, Achilles, Orange-Shoulder, Oriental/Pajama/Lineatus... any others? Hey, no cheating by looking below. All told there are some forty described species in the genus; two "mimics" often mistaken for Dwarf Angels!

Some Acanthurus make hardy captive specimens, others have a dismal aquarium history; most are too poorly known to be judged as yet. Here I'll present my version of who's "good", "bad" and unknown; how to select and maintain the tangs in the genus Acanthurus.

Classification: Taxonomy, Relation With Other Groups

The Surgeonfish family Acanthuridae comprises six genera and about seventy two species. Many are important food and aquarium fishes. Think of the other genera that include the yellow and other Zebrasoma, yellow-tail blue Paracanthurus, various Naso, and less known Prionurus and bristlemouth (Ctenochaetus) surgeonfishes in addition to the Acanthurus. What do they have in common?

All Surgeonfishes are laterally compressed covered with very small scales giving their bodies a leathery appearance. They have long continuous dorsal fins, and small terminal mouths with fine teeth. What really distinguishes the whole family though is the presence of one or more spines on the caudal peduncle (the part of the body right before the tail fin), hence their scientific name from the Greek, acanthus = "thorn". With a twist of the tail these spines are used to as a formidable weapon when needed.

Modern classification schemes divide the six genera of acanthurids into two subfamilies (names ending in "inae") and three tribes (ending in "ini").

The subfamily Nasinae, with one genus (Naso, the Unicornfishes) and seventeen species have two anal fin spines and three soft pelvic fin rays. Several have a frontal "horn" protuberance that gets larger with age. Four branchiostegal (gill supports) rays.

The subfamily Acanthurinae, the rest of the Surgeonfishes, bear three anal fin spines and five soft pelvic fin rays. Five branchiostegal rays.

Tribe Prionurini; one genus (Prionurus), six species; rarely offered in the trade. Have 3-10 non-retractile bony plate "scalpels" on their caudal peduncles.

Tribe Zebrasomini; containing the genera Paracanthurus (one species, the yellow-tail blue), and Zebrasoma of seven species.

The Tribe Acanthurini; genera Acanthurus and Ctenochaetus can be discerned from each other by the six species of Bristlemouths (Ctenochaetus) peculiar long, comb-like teeth. 

Genus Acanthurus ("Ah-Kan-Thur-Us") Species; The Good, The Bad, and The Unknown

Dear Reader, in checking through the voluminous worldwide pet-fish literature which are the anecdotal accounts of hobbyist attempts at keeping this genus, I am struck by several opinions that greatly vary from my own. After handling tens of thousands of these fishes, diving and talking with collectors and public aquarium personnel hundreds of times these are mine... My criteria for "good" species are ones that more than half live three plus months after arrival. "Bad" ones, have behavioral problems and/or a mortality of more than 50% in the first month.

"Good" Acanthurus (One's That Generally Live):

Acanthurus mata Cuvier 1829, the Elongate or Mata Surgeonfish. Indo-Pacific; Red Sea, eastern African coast to French Polynesia, Japan, GBR, Micronesians. Similar to A. xanthopterus lives almost exclusively on zooplankton. Long misidentified as A. bleekeri. To 50 cm.

Natural Range

Most species of Acanthurus are found in the broad area called the Indo-Pacific. One is found in the eastern Atlantic along Africa, five in the Caribbean/western Atlantic.

They are mostly shallow water (1-100 meter depths), rocky and coral reef dwellers.

Size:

Smaller species "only" get six to eight inches, the largest ones to a couple of feet. Under ideal conditions the big ones get that way quickly; growing a handful of inches a year.

Selection: General to Specific

There are four major criteria to consider when judging the acquisition of members of this group; body conformation, color, behavior, and time in captivity.

1) Body Conformation: Though appearance of a pinched stomach is not of itself an accurate indication, healthy, freshly collected specimens of tangs are well-fleshed. The upper body, above and behind the eyes should not be "shrunk in", or show loss of color.

As per minimum purchase size for the genus, I would not buy any specimen under three inches in length.

2) Color should be intense and uniform. You should know that Acanthurus have different stress, fighting, nighttime and reproductive markings and color phases; however prospective buys should show no reddening, erosion, or blotchy discontinuities.

3) Behavior: Tangs that have been captured, transported, acclimated and housed correctly are outgoing and curious about their environment. Avoid hiding, sedentary and "spaced out" individuals having "private parties" in dark corners.

The feeding "acid-test" super-applies to surgeons. They should be eating a variety of foodstuffs at time of purchase.

4) Time in Captivity: I strongly suggest you leave these surgeons a week or two at the dealer's for "hardening". Many questionable animals are lost or otherwise "saved" in this way.

Environmental: Conditions

Habitat

Surgeonfishes by and large fill a niche neither occupied by permanent or transient reef predators, nor by constant smaller denizens like the damsels. Except for the few that are more meat-eaters, they are best described as the algae "lawnmowers" of the tropics. You should keep their habit of constant food searching, scraping and sorting lifestyle in mind when planning their care.

Acanthurus tangs require large amounts of tank space to be truly happy. At adult size, fifty gallons per individual is not too much for modest dimension species.

Chemical/Physical

An important point here concerning the chemical, physical and social environment of these fishes. Keep it optimized and constant! pH should be buffered and maintained between 8.0 and 8.4., temperature kept in the seventies to low eighties F.

Keeping organic levels low to non-existent (no ammonia, nitrite, maximum of 25ppm nitrate) through vigorous filtration, under-crowding and frequent partial water changes is requisite.

Filtration

Keeping Acanthurus surgeons presents a paradox in maintenance. On the one hand they benefit from stable, aged systems with diatom, green algal growth and detritus... on the other, they require low waste loads and high dissolved oxygen.

Make no mistake about this last. Low gas solubility results in loss of color and "gasping" behavior of tangs; panting, laying on the bottom with rapid to slower to no gill movement. Make their water movement and aeration vigorous.

Behavior: Territoriality

For most hobby-size systems keeping one Acanthurus tang to a tank is the best bet. Additionally, by design on your part this fish be designated as the dominant animal in the system.

Except for the species listed as being relatively docile, other Acanthurus should be held in constant suspicion, and watched carefully if any new additions are to be attempted. Field studies bear out this tendency toward agonistic behavior. The home range of these tangs is several square meters; and rarely changing. Except when engaging in "algae-searching" school "fronts" they chase out their own and similar appearing and feeding organisms.

Introduction/Acclimation

How to put this... put these tangs in "last and after a while?" Acanthurus tangs should be placed as the final animal(s) due to territoriality; and given the system's time to "age", stabilize, accumulate detritus and grow some algae.

If you're going to try more than one Acanthurus species or conspecifics, do put them in at the same time, make sure they're of different size (and therefore decidedly not co-dominant), and keep your eyes open for overt aggression.

Predator/Prey Relations

Though they are of spiny-fin, proficient with their razor-like peduncle scalpels, and can be ciquatoxic (poisonous for fish or human consumption), surgeons are consumed by "the usual suspects" predators. Measure those grouper and lionfish mouths twice before introducing Acanthurus.

Reproduction, Sexual Differentiation:

Acanthurus species show little structural or color differences between the sexes. Well, in some the males or females are slightly larger; and male coloring darkens and intensifies at the time of breeding. Take a close look at photographs in the wild of large specimens.

Spawning by species in pairs and schools is tied to lunar cycles, with two or more fishes making mad dashes, releasing their gametes to the surface. These join to become planktonic young that float about for a period of weeks to months. With luck and propitious currents transformed individuals settle down onto a suitable reef.

Feeding/Foods/Nutrition: Types, Frequency, Amount, Wastes

Most Acanthurus surgeonfishes are celebrated algal browsers, tooling along during all daylight hours scouring hard surfaces for plant and associated food. Some members of the genus are known to take considerable animal matter as well; A. thompsoni and A. mata are principally zooplanktivorous. Nearly all will benefit from shrimp, euphausiid, mollusk, other meaty foods included in their captive diets.

But let's not forget to emphasize surgeons' need to nibble on greens. Unless you have but one tiny specimen in a very large tank you'll have to purposely supply vegetable food daily. And more than almost non-nutritive lettuce.

Where oh where can you get enough greens to satisfy these aquatic lawnmowers? Maybe the oriental food section, or collecting your own, or buying it through a bait shop (Ulva & Caulerpa, rhodophytes (re) and phaeophytes (brown algae) are used for keeping bait organisms "fresh").

These fishes need to be offered food frequently; in a perfect world, small amounts all day long. An automatic feeder, stocked with an appropriate mix of dry-prepared foods and set to maximum number of feedings will get you there. As will store-bought or home-grown "algae rocks". You can make these in most any salt-proof container with "old" water change water and calcium carbonate based rock. Provide light and presto! Algae.

Disease: Infectious, Parasitic, Nutritional, Genetic, Social

If anything is more unfortunate than these fishes penchant for fighting, it is their susceptibility to those twin protozoan nemeses of captive marines, Amyloodinium and Cryptocaryon. What's more to woe is the unsuitability of using copper compounds as treatment. This common element in prepared aquarium remedies is of course toxic to the algae and non-vertebrates possibly housed with your tang(s); but it is also incrementally poisonous to the surgeons themselves.

Due to their essential gut fauna, and skin characteristics there is no null zero-effect dose of copper compounds with these fishes. Put another way, they are negatively impacted along with the "bugs" you're trying to do away with when treated with copper. What's an aquarist to do then? Number one, to exercise the usual prophylaxes of quarantine and freshwater dips/baths in moving Acanthurus. Secondarily, the use of facultative biological cleaners (fish, shrimp) is promoted.

Nutritional disorders of tangs are so common a cause of disfigurement and loss that we should mention them here as a disease that should be avoided, and can be "cured". Much work has shown that vitamin A & C deficiencies are a "cause" or co-cause in color loss and head and lateral-line-erosion (acronym HLLE). This pitting may be sent into remission with the feeding of these vitamins. Some aquarists tout the virtues of specific chemical food supplementation; others rely on natural or terrestrial veggie sources (broccoli, carrots...), blanched or frozen.

Close:

Genus Acanthurus surgeonfishes span the range of usefulness and adaptability for captive marine systems. Some are relatively tough environmentally, and easy-going in terms of tankmate behavior. Others have proven to be difficult for all but the most attentive aquarists with large, optimized systems.

Consequential in their successful care is choosing properly captured and transported specimens, providing adequate space, aged, highly circulated and aerated water, and constant provision of appropriate foods.

Bibliography/Further Reading:

Burgess, W.E. 1980. Surgeonfish and angelfish mimics. TFH 29(2):52-56, 58.

Campbell, Douglas G. 1979. Fishes for the beginner, A guide for the new marine hobbyist, Parts three and four, Tangs. FAMA 1,2/79

Colin, P.L.; Clavijo I.E. 1988. Spawning activity of fishes producing pelagic eggs on a shelf edge coral reef, southwestern Puerto Rico. Bull. Mar. Sci. vol. 43, no. 2, pp. 249-279.

Collins, Steve. 1995. Dietary control of HLLE in blue tangs. SeaScope Summer 95.

Debelius, H. 1975? Useful information on surgeon fish. Aquarium digest Intl. #29, pp 31-33., #31, pp 28-29.

Debelius, Helmut. 1993. Indian Ocean Tropical Fish Guide. Aquaprint Verlags, Germany.

Debelius, Helmut & Hans A. Baensch. 1994. Marine Atlas, Vol.1. MERGUS, Germany.

Duarte, C.S.A. & P.A. Acero. 1988. Feeding behavior of the Acanthurus (Perciformes: Acanthuridae) fish genus in the Santa Marta region from the Colombian Caribbean. Rev. Biol. Trop. vol. 28, pp. 399-405. 1988.

Fenner, Robert. 1996. Will the real powder brown tang please swim up? TFH 3/96.

Fenner, Robert. 1997. The Conscientious Marine Aquarist.432pp. Microcosm, VT.

Fishelson, L., Montgomery, W.L., Myrberg, A.A. 1985. A unique symbiosis in the gut of tropical herbivorous surgeonfishes (Acanthuridae: Teleostei) from the Red Sea. Science (Wash.) vol. 229, no. 4708, pp. 49-51; 1985.

Guiasu, Radu C. & Richard Winterbottom. 1993. Osteological evidence for the phylogeny of recent genera of surgeonfishes (Percomorpha, Acanthuridae). Copeia 1993(2):300-312.

Howe, Jeffrey C. 1991. Field observations of death feigning in the convict tang, Acanthurus triostegus (Linnaeus), with comments on the nocturnal color pattern in juvenile specimens. J. of Aquariculture and Aquatic Sciences VI(4):13-15.

Jones, Lawrence L.C. 1988. Care and maintenance of tangs in captivity. Part one: Food and feeding. FAMA 10/88. Part II. Behavior, FAMA 3/84?

Madsen, Pieter. 2000. A Tang by any other name... TFH 6/00.

Maisey, John G. 1996. Fossil surgeonfishes. TFH 4/96.

McKenna, Scott. 1987. Keeping the powder-blue surgeonfish. TFH 36(3):22-25,27.

Montgomery, W.L., Myrberg, A.A., Fishelson, L. 1989. Feeding ecology of surgeonfishes (Acanthuridae) in the northern Red Sea, with particular reference to Acanthurus nigrofuscus (Forskaal). J. Exp. Mar. Biol. Ecol. vol. 132 no.3 pp 179-207.

Moosleitner, Horst. 1992. The brown-eared surgeonfish: A meat eater! TFH 40(6):64-66.

Myrberg, A.A., Montgomery, W.L,. Fishelson, L. 1988. The reproductive behavior of Acanthurus nigrofuscus (Forskaal) and other surgeonfishes (fam. Acanthuridae) off Eilat, Israel. (Gulf of Aqaba, Red Sea). Ethology; vol. 79, no.1 pp. 31-61. 1988.

Nelson, Joseph S. 1984. Fishes of the World. 2nd Ed. Wiley.

Polunin, N.V.C., Harmelin-Vivien, M. & R. Galzin. 1995. Contrasts in algal food processing among five herbivorous coral-reef fishes. J. of Fish Biology 47(1995):455-465.

Randall, J.E. 1956 A revision of the surgeon fishes genus Acanthurus. Pac.Sci. 10:159-235.

Randall, J.E. 1975 Hawaiian fish profiles. ADI 3:2, pp 12,13.

Randall, J.E. 1986. Acanthuridae; in Smith's Sea Fishes. Springer-Verlag, Germany. pp. 811-823.

Randall, J.E. 1988. Three nomenclatorial changes in Indo-Pacific surgeonfishes (Acanthuridae). Pacific Science 41(1987):54-61.

Recksiek, Conrad W., Appeldoorn, Richard S. and Ralph G. Turingan. 1991. Studies of fish traps as stock assessment devices on a shallow reef in south-western Puerto Rico. Fisheries Research 10(1991):177-197.

Sands, David. 1994. Superb surgeons. FAMA 10/94.

Stratton, Richard F. 1988. The blue tang. TFH 1/88.

Stratton, Richard F. 1989. The achilles tang. TFH 1/89.

With the permission of Robert (Bob) Fenner webmaster of WetWebMedia (robertfenner@hotmail.com)

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