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David Bell, Bob Fenner
part of our "species-centricity" is born out by our greater awareness and knowledgeable appreciation for the terrestrial world rather than the aquatic. Everyone gasps in awe at seeing magnificent Redwoods - "Look at all that fixed carbon!", some say. There is a broad difference here though between such measures of "standing crop" versus "primary productivity" on the world's reefs. Imagine removing some ninety percent of the life from both environments and coming back a year later to measure the expected regeneration. Not surprisingly, the new growth redwoods would barely approach "sapling-hood," but the reefs would hardly appear different than before they were stripped down. Such is the amazing productivity of these aquatic environments called reef systems.
Now, on the downside, as aquarists, we're all too familiar with the propensity for algal "lawns" overgrowing our systems, and in short order. But in diving and snorkeling on reefs, there are rarely such visible "algae problems" detected. Is it really too much phosphate, nitrate, and crowded conditions that account for such profuse greenery in marine aquariums? Or, do you need that bigger, better skimmer or some other gear after all? Well, the root cause(s) of algae woes can be these and more, but it is a certainty that wild environments have much more "check and balance" going for them in the way of nature's reply, the "algae eaters." Experiments performed on reefs in the wild point to the Surgeonfishes fulfilling the role of algal grazers. When excluded from a tropical rocky reef area by simple netting, the site can be quickly overgrown without continuous Acanthurid grooming, literally within days. Such prodigious activity as algae nibbling is of tremendous utility to marine aquarists, particularly reefers, as troublesome attached micro- and macro-algae in profusion is a cause of much trouble and consternation. This prodigious group of micro- and macro-herbivores are the several algae eating Surgeonfishes of the family Acanthuridae, one of the reef's more proficient algal "check and balance" systems.
Whatever common name may be applied to these razor-wielding Acanthurids - the Surgeons, the Tangs or the Doctorfishes - they span the entire bandwidth of aquarium suitability; some are exemplary specimens, a few ship so poorly that they rarely recover from the rigors of capture and transport from the wild, then there are the members of the family that should be disqualified on the basis of their mature size - quite a few grow to more than two and a half feet in length - and, how about those with outright antagonistic behavior? The majority, though tough as proverbial "nails," must still be qualified through careful individual selection on the basis of disposition, apparent condition, and proven feeding, all variables which will determine the measure of success in maintaining members of the Acanthuridae in the aquarium.
Classification and Physiology
Surgeonfishes are part of a loose assemblage in the largest order of fishes, the Perciformes, in the sub-order Acanthuroidea. Relatives include the Rabbitfishes of the family Siganidae (a notable member is the Foxface), the Scats of family Scatophagidae, and the exquisite Moorish Idol of family Zanclidae. Consider the physical traits that these family's member species have in common; bodies that are deeply laterally compressed and covered with very small scales, presenting a leathery appearance, as well as small mouths with fine teeth, relatively large swim bladders, and elongate nasal bones that give a high-headed appearance. They all have a single dorsal fin with spines and soft rays, smallish gill openings, lunate caudal fins, long continuous dorsal fins, and 22 or 23 vertebrae. In addition, the Acanthuridae are truly distinguished by their elaborate spine-locking mechanism (a recessed groove for the first dorsal and anal fin support) and the presence of one or more knife-like projections they bear on their caudal peduncles (the part of the body to the fore of the tail fin), hence their scientific name from the Greek, Acanthus, meaning "thorn." With a twist of the tail these spines are used as a formidable weapon when needed. The Surgeonfishes can and will use them adeptly when threatened.
Size-wise, the Surgeonfishes range from just a few inches to almost three feet in total length.
All Surgeons are principally herbivorous, feeding mostly on algae. Another salient characteristic is their passing through a bizarre transparent larval stage termed the acronurus stage.
Also called Doctorfishes and Tangs, the Surgeonfish family of Acanthuridae, with its six genera and seventy-two species, should be familiar; several members are used for display in marine aquariums and they also fill a role as food fishes. Where would our hobby be without such favorites as the Yellow Tang and other Zebrasoma species, the Yellow-tail Blue of Paracanthurus, various Naso and Acanthurus species, and the lesser known Bristlemouth Surgeonfishes of Ctenochaetus, in addition to the Prionurus?
Modern classification schemes divide the six genera of Acanthurids into two sub-families (names ending in "inae") and three tribes (ending in "ini").
The sub-family Nasinae, with one genus, Naso (the Unicornfishes), and seventeen species, have two anal fin spines, three soft pelvic fin rays, and four branchiostegal (gill support) rays. Several have a frontal "horn" protuberance that gets larger with age. The sub-family Acanthurinae, the rest of the Surgeonfishes, bear three anal fin spines, five soft pelvic fin rays, and five branchiostegal rays.
Of the Tribe Prionurini, there is one genus, Prionurus, and six species which are rarely offered in the trade. The Prionurus have 3 to 10 non-retractile bony plate "scalpels" on their caudal peduncles. The Tribe Zebrasomini contains the genera Paracanthurus, of which there is one species, the Yellow-tail Blue Tang, and the genera Zebrasoma with seven species. The genera Acanthurus and Ctenochaetus, of the tribe Acanthurini, can be discerned from each other by the six Bristle-mouth species of the family Ctenochaetus with peculiarly long, comb-like teeth.
Surgeonfish Species of Interest to Reef Aquarists
As with other potential livestock groupings, not all Surgeonfishes are suitable or useful for reef aquarium keeping. Many get way too big (those that approach three feet in length), others are more generalized in their feeding strategies (one is a carnivore!), and several of the species that hobbyists try way too often have miserable rates of survival in captivity. Presented below are our beliefs concerning which species are most desirable and those that should be avoided by the reef hobbyist, as well as some notes on their selection and practical husbandry.
Of principle interest to reef aquarists are the Sailfin Tangs of the genus Zebrasoma and the Bristle-mouth Tangs of the genus Ctenochaetus, as these fishes are superb algae scrapers and pullers, staying small, with all species of these genera proving relatively hardy. However, the monotypic Pacific Yellow-tail Blue Tang in its family Paracanthurus and a few of the smaller Acanthurus deserve mention as well. The other two genera and some commonly employed species of surgeons that should be avoided will also be discussed.
Superb selections for the reef aquarium, the members of the genus Ctenochaetus ("ten-oh-key-tus") are commonly called the Bristle-mouth Tangs. This is a genus whose members are attractively shaped, colorfully marked, and behaviorally interesting … and, they are great algae eaters. In fact, their mouths are so well-defined for such a task that Bristle-mouth Tangs can actually remove diatoms! All six Ctenochaetus species do well in captivity given the selection of initially healthy specimens and the provision of algae and detritus in an older, established, not-too-clean system, and especially one with live rock. Here are some pertinent notes regarding the three species of Ctenochaetus most frequently offered in the trade:
Ctenochaetus hawaiiensis (Randall 1955), the Chevron Tang; like all Ctenochaetus species this one changes color with age but the Chevron is the most striking juvenile of the genus. C. hawaiiensis young are extraordinary in overall appearance; bold, orange bodied, covered with variegated lines of electric blue. Adults shift to a deeper orange-red base covered with darkish blue uneven horizontal lines, ultimately changing to almost black. This species is found widely around the Pacific Plate, but never in great numbers. The best specimens come out of Hawaii, the species namesake and most common source. C. hawaiiensis is collected in fifty feet plus depths of water.
Ctenochaetus striatus (Quoy & Gaimard 1825), the Striped Bristletooth; one member of the genus found extending into the Red Sea, but also found in the Indo-Pacific to Oceania and the Indian Ocean; and, the most frequently imported species of this genus in Europe. The body color of C. striatus is overall drab olive, sporting wavy blue lines with small orange dots sprinkled on the head.
Ctenochaetus strigosus (Bennett 1828), the Yellow-eyed or Kole Tang; having a range encompassing the principal islands of Hawaii, from where it is most often collected, extending all the way westward to the east coast of Africa. The Kole ("coal-ay") is more a shallow water species found from the surface to depths of sixty feet or so.
Ctenochaetus tominiensis (Randall 1955), the Tomini Bristletooth, is occasionally shipped from the Philippines. Of the four regularly available species of Ctenochaetus, the Tomini Bristletooth, is the most difficult to keep.
There are a couple of other credible species of Ctenochaetus that we'll mention in passing for the sake of thoroughness, though they are rarely available to the aquarium trade:
Ctenochaetus marginatus (Valenciennes 1835), this Indo-Pacific fish bears a strong resemblance to C. striatus but may be distinguished by its redder color and squarer caudal fin profile. C. cyanoguttatus is a junior synonym for this species.
Ctenochaetus binotatus (Randall 1955), the Blue-eye or Two-spot Bristletooth, for the two dark areas at the rear of the dorsal and anal fin bases, is sometimes shipped from the Philippines.
Of all the genera of Surgeonfishes, the seven species of Zebrasoma rank supreme with reef and general marine aquarists. The Zebrasoma Tangs are hardy, beautiful, and semi-peaceful, all. These disc-shaped Surgeons are the most adaptable of the family, readily accepting all sorts of aquarium foods and adjusting to the relatively small volumes of aquariums quite well. They are the highest rated in terms of disease resistance and treat-ability amongst all Surgeonfishes. In addition, these fishes thrive on filamentous algae:
Zebrasoma desjardinii ("day-har-din-ee-eye"), Desjardin's Sailfin Tang; seeing this fish and Z. veliferum at the same time might cause you to do a double take, they are so very similar in color and markings. However, as a point of fact, Desjardin's Tang is currently an invalid species name (nomen nudum), and this Sailfin Tang is considered synonymous with Z. veliferum. We will list or mention it here as it will likely be encountered sold as Desjardin's in stores. This "variety" comes to the trade mainly from the Indian Ocean or Red Sea, so one way to distinguish it is by source locale, and still another is by its price. It also has a few less soft dorsal and anal fin rays (28,29D and 22-24A versus 29-33D and 23-26A for the Pacific Sailfin), if you can get yours to hold still while you make the count. Actually, the easiest discernible difference is in the markings on the tail. The Pacific is white, yellow and gray banded, and Desjardin's is dark with whitish yellow spots.
Zebrasoma flavescens (Bennett 1828), the Yellow Sailfin Tang; a "standard" in the marine aquarium hobby if there ever was one. Only certain Damselfish species grace the tanks of aquarists more frequently than Z. flavescens. The Yellow Sailfin Tang makes up the bulk of pet-fish collected out of Hawaii, and rightly so; it fares best from there. With their conspicuous golden yellow color, active nature, persistent algal grazing and hardiness, yellows make long-term and pleasing additions to the reef aquarium.
Zebrasoma gemmatum (Valenciennes 1835), the Spotted Sailfin Tang; an appropriately named species in the vernacular and scientifically; that is, spotted, and as rare, beautiful and expensive as a precious stone. This Indian Ocean endemic is rarely imported to the west, and what a shame. It is just as hardy as any of the other Zebrasoma species and a real beauty.
Zebrasoma rostratum (Gunther 1875), the Black Longnose Sailfin Tang; restricted to the Pacific, Polynesian island groups, the Tuamotus, Societies and Pitcairn. In many ways, just a darker, longer-snouted version of Z. scopas or Z. flavescens with a rostrum up to 30 percent of its total body length. Likewise, Z. rostratum is also a hardy, undemanding reef aquarium specimen.
Zebrasoma scopas (Cuvier 1829), the Brown, or even more aptly named, the Two-tone Sailfin Tang. The former common name can be a bit of a misnomer, so we will use the latter; Z. scopas specimens have been noted as brightly yellow as a Z. flavescens and as dark as a Z. rostratum. As juveniles they're different still, with light colored fronts grading out to dark variable spots and lines. Occasional "dirty" or mixed-color crosses between the Two-tone Sailfin and Z. flavescens are encountered along their contiguous distributions which are widely ranging in the Indo-Pacific.
Zebrasoma veliferum (Bloch 1795), the (formerly Pacific) Sailfin Tang; collected out of the Philippines and Indonesia, though better out of Hawaii, Ceylon and other locales in the eastern Pacific. Some call this THE Sailfin Tang for its majestic array of flowing dorsal and anal finnage, making it especially over-sized in appearance when young. Most other species of Sailfin Tangs grow to about eight inches in length in the wild, this particular species to about twice that.
Zebrasoma xanthurum (Blyth 1852), the Yellow-tail or Purple Sailfin Tang; Z. xanthurum is collected from the Red Sea and its southern mouth. This is a supreme and gorgeous aquarium fish; hardy and unmistakable with its bluish purple body and yellow pectoral and caudal fins. Proper diet is paramount in maintaining the lavish colors of Z. xanthurum.
Alone in its genus is a species of many names, Paracanthurus hepatus (Linnaeus 1766); this monotypic species is also commonly called the Pacific Blue, Yellow-tail Blue, Regal, Palette or Hippo Tang. Regardless of its common name, P. hepatus are so highly prized as to be used extensively in the hobby and trade and so robust as to be a "standard" in the aquarium service industry. Specimens that have been collected, housed, and selected properly are excellent long-term livestock; however, most of the problems contributing to their loss are unacceptable methods of capture, initial over-stress, lack of nutrition, and poor water quality. Widely collected in its Indo-Pacific range, better specimens come out of New Caledonia, Kiribati and Australia. Acanthurus make hardy captive specimens while others have a dismal aquarium history, still a handful are too poorly understood to be judged as yet. Of the thirty-eight species of the Surgeonfishes of Acanthurus ("Ah-Kan-Thur-Us") many are simply too big and too messy for the typical hobbyist's reef setup. However, the genus does offer a mixed bag; there are easier-going smaller species which demand consideration, even in light of the larger group of too large and too fragile types that hobbyists should, but don't always, avoid. We will present the pluses and minuses of these individuals while identifying those species that are quite acceptable and manageable in captive reef systems:
First, there are the "good" Acanthurus species; the one's of manageable use, of diminutive stature, and generally remaining alive beyond acceptable minimal durations:
Acanthurus bahianus (Castelnau 1855), the Ocean Surgeon; ranging widely over the western Atlantic coast. It's a shame this hardy fish isn't more often available in the trade. It has a subdued, yet impressive beauty. Although not superbly-gorgeous, it is one of the least aggressive Acanthurus, and the readiest feeder on aquarium fare.Acanthurus coeruleus (Bloch & Schneider 1801), the Atlantic Blue Tang; though not as dazzlingly beautiful as the other two "Blue Tangs" - Paracanthurus hepatus and Acanthurus leucosternon - this Caribbean surgeon makes a fine aquarium addition. One of a handful of Acanthurus that are overall yellow as juveniles, the Atlantic Blue Tang stays small enough for modest sized aquariums.
Top left: brightly colored juvenile A. coeruleus; Top right: transitioning to adulthood; Bottom: a full size adult Atlantic Blue
Acanthurus dussumieri (Valenciennes 1835), the Eyestripe or Dussumier's Surgeonfish, can sport a great degree of color variation. Some are drab gray, whereas some from Hawaii exhibit brilliant yellow around their body margin with beautiful royal purple highlights. This surgeon is more like the genus Ctenochaetus in its feeding habits, sifting sand and detritus in addition to algae scraping.
Acanthurus japonicus (Schmidt 1931), the Japan or White-Faced Surgeonfish; mis-sold at times as the Gold-Rimmed or Powder-Brown Surgeon, being confused with Acanthurus (glaucopareius) nigricans. To delineate the species, A. japonicus has a much larger white eye patch than the Gold-rimmed or Powder-Brown. A. (glaucopareius) nigricans ranges in distribution from the Philippines to Japan and is relatively hardy, specimens achieving up to eight inches in length.Acanthurus nigrofuscus (Forsskal 1775), the Brown or Spot-Cheeked Surgeonfish; a species that reaches a manageable size - to eight inches - and displays moderate behavior toward other fishes. These attributes qualify the Brown Tang as a desirable aquarium species, especially when considering its ability to control algae, but unfortunately, in appearance it is a rather plain and drab fish comparatively.
Acanthurus sohal (Forsskal 1775), the Red Sea Clown or Sohal Tang. Our vote for the best Surgeonfish of the genus Acanthurus, though some individuals get quite aggressive with age and size. As long as they considered the "kingfish" and given ample room to roam in large aquariums, problems are few.
The Sohal Tang, A. sohal: a hardy but more aggressive species demanding room to roam
Acanthurus thompsoni (Fowler 1923), the White-Tailed Surgeonfish, normally a good name for this species except for those populations in Hawaii which bear no white on their tail areas. Another name for this planktivore is Thompson's Surgeonfish. Though not particularly striking, this fish is a good feeder and remains moderately small among a family of bruisers, growing to ten inches in the aquarium. However, A. thompsoni is rarely imported into the aquarium trade.
Hawaiian reef scene: Juvenile A. triostegus
Acanthurus triostegus (Linnaeus 1758), the Convict Tang or Manini (Hawaiian); is one of the best Acanthurus for use in reef tanks; noted for its size, easy going temperament, and habit of consuming fine, filamentous algae. Groups of A. triostegus make for an attractive display in larger reef systems.
A good time to mention the Mimic Tangs, these Acanthurus species "pretend" in color, markings, and behavior to be other species. In this case, pretending to be Dwarf Angelfishes of the genus Centropyge; the specific advantage accrued is that of reduced predation as the Dwarf Angels are spiny and feisty, traits which may drive away would-be antagonists.
The Acanthurus Mimic Tangs should be considered "good" aquarium species primarily due to their slow growth rates (can be kept as juveniles for years), their peaceful nature (to the point of over-shyness), and their readiness to eat prepared foods. Mimic Tangs thus make excellent reef tank inhabitants. Of note are the following Mimic Tangs of the genus Acanthurus:
Acanthurus chronixis (Randall 1960), the Chronixis or Mimic Surgeonfish; very similar to Centropyge vrolikii, with an anterior which is two-thirds silver-gray, a deep black posterior, and identical blue highlights on its unpaired fins.
(picture of A. chronixis)
Acanthurus pyroferus, the Chocolate or Mimic Surgeonfish; as juveniles this species may appear similar to Centropyge eibli, Centropyge heraldi or Centropyge flavissimus.
Acanthurus tristis (Tickell, 1888), the Indian Mimic Surgeonfish, like A. pyroferus also imitates the dwarf angel Centropyge eibli. This Surgeon is a good fish for the reef aquarium, attributable to its moderate size and less than average aggressiveness. (picture?)
Then, there are the "bad" Acanthurus species. Just what makes an Acanthurus Tang species "bad" besides dying easily in captivity?….well, NOT dying easily, but instead, helping your other livestock to do so. Honestly, some individuals of the fishes listed below can end up killing all their tankmates, through disease introduction or by outright aggression. If you are dead set (no pun intended here) in trying these species in your reef systems, do your best to prevent parasitic introduction and stock the aggressive Acanthurus specimens with similarly tough fishes only…and, even then keep your eye on them for changes in temperament and for aggressive outbursts:
Acanthurus achilles (Shaw 1803), the Achilles Tang; remarkably exotic in coloration and impressive in overall appearance. A. achilles is widely distributed from Hawaii, westward through Micronesia and Melanesia, with the best specimens hailing from the 50th U.S. state. Success with this soft-bodied species can only be had from securing a healthy specimen initially, providing a large living space, and high, consistent specific gravity and oxygen concentration.
Acanthurus leucosternon (Bennett 1833), the Powder Blue Tang; besides being notorious carriers of parasitic diseases, most specimens don't even make it through the capture and shipping stages. But…some of you are screaming, "this isn't a difficult fish!…I've known people to keep the Powder Blue for years!" Those healthy few that are well received and cared for - with lots of live rock and algae in large, well-established reefs - do occasionally live for extended periods.
Acanthurus lineatus (Linnaeus 1758), the Clown, Pajama, or Oriental Surgeon; undoubtedly attractive to unwary reef aquarists, this is a "bad" fish for something in addition to difficulty in feeding and its high mortality rate…..its territoriality. Though this is a commonly used species when small, this fish can become an unholy terror towards its tankmates, getting progressively worse with growth. In the wild it reaches fifteen inches in overall length.
Acanthurus (glaucopareius) nigricans (Linnaeus 1758), the Powder Brown, Cat, or Gold-Rimmed Surgeon. The corrected scientific name of this species is A. nigricans (per Randall, 1988); a revision which is no doubt as unpopular to some as is labeling the species "bad". The very similar A. japonicus is a far better aquarium fish. A. nigricans rarely lives for more than a few weeks in captivity.
Acanthurus olivaceus (Bloch & Schneider 1801), the Orange Spot or Orange Shoulder Tang; a hardy fish out of Hawaii and elsewhere, but unfortunately, a behavioral terror in the ranks of A. lineatus. This is an active fish that grows to more than a foot and a half in length. It should only be placed with other "mean" tankmates in the confines of a huge aquarium.
There are other remaining Acanthurus Tangs and six species of Prionurus Tangs but all get too big - many to two feet eventually - to be of use to the home reef hobbyist.
The sixteen species of Naso ("Nay-zoh") Tangs share the traits of being open, active swimmers, and a propensity for getting BIG. Unless you have an absolutely huge reef system of hundreds of gallons, you're strongly encouraged to only try the species of Surgeonfishes suggested previously. Here, we'll expand only on the five Naso species that are principally available in the hobby worldwide:
Naso brevirostris (Valenciennes 1835), the Spotted Unicornfish, sometimes called the Shortnose Unicorn Tang; mis-named both scientifically and colloquially. N. brevirostris has a long nose as an adult and there are Naso species with much shorter snouts; some Unicorns are even absent the "horn" protuberance on the head. This grayish-green bodied fish is occasionally imported from Hawaii and the Indo-Pacific. It can reach two feet in length.
Naso lituratus (Forster 1801), THE Naso to most aquarists, or otherwise the Orangespine, Tricolor or Lipstick Tang. There are some who claim that "blonde" and "streamer" versions are different species but they're all Naso lituratus. The species will grow to eighteen inches in the wild and it is simply outright cruel to keep one in a too small, or too short system in captivity. Minimum acceptable tank length is 4 feet.
Naso unicornis (Forsskal 1775), the Bluespine Unicornfish; a deep-bodied species that develops a prominent rostral horn starting at about five inches in length. The body is light olive to gray with yellowish highlights on the abdomen, attaining a length of more than two feet in the wild.
Naso vlamingii (Valenciennes 1835), Vlaming's Unicornfish; the species has naught but a convex nose bump for a horn. Adult males are especially beautiful with bright blue and white highlights over a dark blue body, also attaining a length of more than two feet in the wild. (picture would not format)
Selection is addressed from the "general" to the "specific". There are five major criteria to consider when judging the acquisition of members of this family; 1) body conformation, 2) size, 3) color, 4) behavior, and 5) time in captivity; and, for the purposes of our evaluation, we will add a sixth, 6) the country of origin:
1) Body Conformation is an indices of fitness, and maybe most preeminent in accurately gauging fitness is the degree of undernourishment that is in evidence. In selecting specimens, pay specific attention to the loss of flesh in the upper body, particularly the area above and behind the eyes. This area should not be shrunk in, appear bony or show a loss of color; but on the other hand, the appearance of a pinched stomach is not always of itself an accurate indicator. Take a look at wild Surgeons in coffee-table books and "It's-the-end-of-the-world" nature shows on television. Notice how robust and outright porky these fishes are. Undernourished fishes should be considered diseased as such, and are far more susceptible to other diseases as a consequence of this stress. the feeding "acid-test" doubly applies to surgeons; it is a "good" indicator if they are eating a variety of foodstuffs at the time of purchase. Ultimately, comparative values can only be ascertained on the basis of a working knowledge of the proper overall appearance; color, conformation and comportment of healthy, freshly collected specimens; in simpler terms, there is no substitute for experience in selection. Observe as many specimens as possible and become familiar with bodily conformation in order to make "conscientious" selections.
2) As for size, smaller species will usually realize only six to eight inches in total length in captivity while the largest ones may attain two feet or more. Under ideal conditions, the "big" Acanthurids attain larger proportions more quickly, growing a handful of inches a year. As size is considered during the purchase of these fishes, buying any Tang under three inches in length is not endorsed. In turn, larger specimens or adults will generally acclimate with more difficulty.
3) Color should be intense and uniform. True, when an individual is stressed or "out of phase" from being in the dark, they will naturally be off-color; however, there should be no reddening, erosion, or blotchy discontinuities in healthy specimens.
4) Behavior, or mannerisms - the way a fish handles itself in a dealer's system - is also telling. Tangs that have been captured, transported, acclimated and housed properly are outgoing and curious about their environment. Avoid hiding, sedentary and "spaced out" individuals having private parties in dark corners. Is the fish active, curious, swimming about, "sampling" it's environment? Or is it sort of spaced out, drifting, unaware of what's going on around it? Trained observation will discern the ideal selection from the one that should be left behind.
5) Time in captivity: How long has the supplier had the Surgeon? Acanthurids are subject to extensive alimentary faunas (critters living in their stomachs). These populations of micro-organisms appear to be benign to at least tolerably non-pathogenic in the wild. There may be uncertainty that this is the case in captivity. Allowing some settling time of a week or two in the dealer's for "hardening" with or sans deposit is warranted and credible businesses should always oblige the reef-keeper in such matters.
In the case of the Surgeonfishes, there is one other additional vital factor concerning selection:
6) Buy local and act global. Can you stand one more gross generalization? Good, well here's a beauty…buy American. No, we really are serious in this case, and not for any patriotic inclinations. For various reasons, the same species collected in Hawaii, Guam, among other U.S. locales are by and large in better condition than elsewhere. Chalk it up cumulatively to regulation, greed for the almighty buck by providing a better product, regular utilities, and who knows what, but the fish are simply better.
Location / Environment
Surgeonfishes, as a family, are circumtropical and entirely marine, mostly pelagic reef fishes, though some are oceanic. They are prominent species in shallows to a few hundred feet on rocky and coral reefs worldwide. Most are found in the Western Pacific, with only nine species in the Atlantic and four in the Eastern Pacific.
When considering habitat, the larger open-ocean bound species like Naso Tangs require very large amounts of tank space to be genuinely happy. Even Yellow and Yellow-tail Blue Tangs can only get along on a ten gallon allocation at minimum when they are small. In order to be truly "conscientious" reef aquarists, shouldn't we ensure the "species size" vs. "space requirements" ratios for our charges?
An important consideration concerning the chemical, physical and social environment of these fishes is to keep these components and factors optimized and constant! Numerous authors cite the loss of livestock by moving or changing conditions. As an example, I'd like to offer my inclusion of an "environmental disease" of Achilles tangs - Many fish-only systems have their specific gravities manipulated to be lower than the ocean for valid reasons; to save money, control/prevent epizootics, and increase gas solubility, for instance. Acanthurus achilles does not appreciate it. Keep their salinity near that of the ocean, and homeostatic. Likewise pH should be buffered between 8.0 and 8.4, and temperature for all but the Caribbean species should remain in the upper seventies to low eighties degrees Fahrenheit.
In addition, keep organic levels low to non-existent through vigorous filtration and skimming, under-crowding, and frequent partial water changes. However, many, if not most, Surgeons are openly detritivorous, picking up important biological and mineral material from scrounging around in rock and sediment. Therefore, it is important to not be absolutely meticulous in such maintenance; however, well-established reef settings with lots of live rock is the most conducive setting for all Tangs.
One absolute requirement of the family is to maintain oxygen levels that are close to saturation. Low gas solubility is immediately evident in the loss of color and behavior of Surgeons. They will pant and lay on the bottom with rapid, to slower, to no gill movements.
Behavior / Characteristics / Compatibility
Territoriality can be a very big problem regarding 1) relative sizes, 2) relationships of species one to another, 3) size of the system, 4) number of fish and other livestock in the system, 5) order of introduction to the system, 6) and, individual personalities. For practical purposes, one Tang to a tank is a safe bet. Very rarely do the more disc shaped species such as Yellows, Convicts, or Browns mix well in a small system. The larger species in the genus Acanthurus should be designated as the dominant fish in the system.
Except for foods and feeding concerns, crowding Surgeons by the species (or sometimes mixed) is okay for the schooling types available. Indeed, a small schooling group in a very large system (hundreds of gallons) makes for a spectacular showing. However, take note: even the species only encountered in schools in the wild, such as Convicts, Nasos, and Yellows fare well singly.
There are exceptions to the easy-going behavior, both as individuals and species. Some individual Oriental Surgeons have been known to be particularly vicious towards subsequently introduced species and their own kind, so be aware that there are some general and specific exceptions. As for their use in reef systems, they do not generally attack invertebrates and almost always prove useful for algae control.
When introducing and acclimating a Surgeonfish to its new environment, special consideration should first be given regarding capture and/or netting; think and prepare before attempting this. Surgeons are powerful swimmers and those scalpel-like projections are sharp and they will show no trepidation in using them to cut you. Consider the mesh of your nets; Tangs are easily tangled (yeah, this pun intended). Use two nets, guide and direct with one and swoop up under the intended with the other. Also pay attention to the stout spines in the anterior dorsal and anal fins; they are sharp and tend to get the skin torn off when moving the specimen. Some Surgeons, like Yellow-tail Blues, have a propensity of swimming into and lodging themselves within coral, rock, and other d?or. Do not try to dislodge them from their protective cover! If you are purchasing the specimen, you should either purchase and transport the d?or with the fish, wait it out, or simply get another specimen. Attempting to remove the fish will first add to its stress and may also impose injury from which the animal may not be able to recover. If all this wasn't involved enough, some Tangs are known to be venomous! Enough said? Handle them carefully.
If at all possible, introduce your Surgeonfish(es) as the last additions. This will aid in reducing antagonistic encounters since other livestock will have already staked out their home turf.
Conscientious consideration should be given to predator and prey relationships that will inherently exist in captive environments. This goes, not only for systems where Surgeonfishes are housed, but for any captive reef environment. There are many large predatory reef fishes that naturally prey upon surgeons in the oceans. There are even countries where people utilize small Acanthurids as bait! Keep your tangs with basses, eels, and others that have smaller mouths and appetites than your tang's diameter.
It would be remiss not to mention at this point that the flesh of various Acanthuridae species, at different times, are suspected and known to contain deadly amounts of ciquatoxin, therefore proving toxic for human, and possibly other fish, consumption… so don't eat them!
Foods, Feeding and Nutrition
Have you ever tried to live solely on iceberg and romaine lettuce? Not very satisfying or nutritious. Along with various other human greens; peas, kale, okra, spinach, and more, pet-fish ichthyologists have tried to sustain or augment the diets of Tangs. Many of these contain too much oxalic acid; all have too little nutritive value. In the wild, disparate Surgeon species digest different mixes of species of algae and their interstitial fauna. You can and should come as close to this make-up of foodstuffs as practical. Some suggestions: Make your way to the oriental food section of your local mega-food-market or specialty store and check out and try their assortment of fresh, prepared, and dried seaweeds. Also, experiment with commercial "green" preparations and even try making and using a homemade paste food. There are a few of these offered in the references listed below. If space, time, and budget allows, collect your own, or buy through a bait shop, greens like Ulva and Caulerpa, rhodophytes (red algae), and phaeophytes (brown algae) for keeping bait organisms "fresh". An occasional "live rock" with micro- and macro-organisms goes a long way towards making the tank and it's inhabitants happy. Very young Surgeons are planktivores and most adults will consume a modicum of brine shrimp, Euphausiids, and such, but will not be sustained indefinitely on them. Whatever you're offering, do so often. Invest in a small battery operated automatic feeder, stock it with an appropriate mix of dry-prepared foods, and set to the maximum number of feedings. Except when sleeping, surgeons are constantly on the prowl for edibles. Contrarily, don't lose your mind if a new specimen or even an old one gives up eating for a time. There are records of hunger strikes among Surgeonfishes lasting weeks without loss.
Reproduction and Sexual Differentiation
Acanthurids have not been successfully spawned and reared in captivity as yet. No great sexual dimorphism or dichromatism (structural or color differences) have been described for any species. Various species have been seen congregating in pairs and schools tied to lunar cycles and darting in pairs to the surface, releasing floating gametes.
The Surgeonfishes often receive quite undeserved attention regarding their presupposed over-susceptibility to the saltwater protozoan parasites Cryptocaryon and Amyloodinium. Truth all told, most marine livestock captured in the wild typically carry some internal and external parasitic "load". These infestations may be triggered or exacerbated through the stressful capture and transportation process.
I want to mention my old graduate school roomie's work/thesis on a free-living flatworm "space parasite" commonly found on non-dip/treated yellow tangs (Hey Mike!). This brownish/black pin-head sprinkling is not dangerous in itself, except that it frequently leads the aquarist to panic and kill off everything through over- and mis-treatment. (Image: micrograph of Paravortex) Effective administration for this problem and most other treatable ectoparasitic infestations and infections involves the prophylaxes mentioned above, copper and preventive freshwater baths. The use of facultative biological cleaners (fish, shrimp) is also promoted.
We should re-mention the avoidance of all specimens with evidence of hemorrhaging, generally indicative of Vibrio, Aeromonad, or other bacterial infection. These fish are goners. Only in rare cases have we seen effective cures.
Nutritional disorders of tangs are so common a cause of loss that we will mention them here as a disease that should be avoided, and can be "cured". Much work has shown that vitamin C deficiency is a "cause" or co-cause in color loss and lateral-line-erosion. This pitting may be sent into remission with the feeding or addition of this transient vitamin.
Surgeonfishes span the entire range of usefulness and adaptability for captive reef and general marine systems. Some are relatively tough environmentally, and easygoing in terms of behavior and compatibility. 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, mainly greens best provided as part of live rock. The species endorsed here for algal control in reef systems rank supreme in usefulness for reefs.