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.
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.
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.
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.
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.
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.
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.
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.
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.
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