Paracanthurus hepatus (Blue Tang)
Of the more than ten-thousand species of marine fishes, only a few hundred regularly grace our marine aquariums. Size, ease of capture and transport, availability of air-freight are some of the limiting factors on the supply side; beauty, adaptability to captive conditions, and hardiness are some of the prominent demand criteria.
The surgeonfish family garners more than it's share of these top slots as choices for marine systems. Several of its members have proven aquarium-tough. Disease resistance, food acceptance, brilliant color and markings are high marks for quite a few tang species. In particular two, the yellow Zebrasoma, and yellow-tail blue tang, Paracanthurus hepatus are highly prized. The latter is used extensively in the hobby and trade; so robust as to be a "standard" in the aquarium service industry.
Surprising to me however, many aquarists are hesitant to stock Paracanthurus, stating low success in keeping them alive, and early loss to "hole in the head disease", or "anomalous" causes.
Yellow-tail blues that have been collected, housed and selected properly are excellent long-term livestock; most of the problems associated with their loss are initial over-stress, lack of nutrition, and poor water quality. Here are my observations, borrowed facts, ideas and methods concerning this species.
Classification: Taxonomy, Relation With Other Groups
The six genera and seventy two or so species of surgeonfishes (family Acanthuridae) are classed within the largest Order of true bony fishes, the Perciformes. The suborder that contains them (Acanthuroidei) includes the difficult Moorish idol (family Zanclidae), venomous rabbitfishes (family Siganidae), the delightful scats (Scatophagidae), the spadefishes, Ephippidae, that currently include the batfishes (Platax), and an obscure foodfish called the louvar (family; you guessed it, Luvaridae).
These six families of fishes are bundled together taxonomically as acanthuroids for their sharing of an equal number of technical internal characteristics. They are all marine, generally herbivorous with moon-shaped tail fins, and their juveniles pass through a salient transparent planktonic larval stage in called an acronurus.
The surgeonfish family itself comprises six genera, all with more than one species except our fish du jour. Paracanthurus can be distinguished from all other tangs by its distinctive coloration, and if you look closely, the possession of only three soft pelvic fin rays (others have five).
The monotypic genus Paracanthurus is most nearly allied with Zebrasoma; and for practical purposes the yellow-tail blue shares most of its husbandry parameters with the sail fin tangs.
A quick mention re the "other" blue tang(s); you'll run into at least the Atlantic Acanthurus coeruleus. It's a beauty too, but obviously a seperate species.
Natural and Introduced Range
Paracanthurus hepatus, has many common names; it is sometimes known as the regal, or flagtail surgeonfish; aka the hippo or palette tang in the west. The last is my favorite, as the palette tang does exhibit the brightest artists' blue, black and yellow. It ranges widely throughout the reefs of central and Indo-Pacific, to Africa's east coast, singly or in small schools.
To about a foot total length in the wild, half that in captivity.
Selection: General to Specific
Index of fitness, is a fisheries measure of relative chubbiness, body circumference divided into length. A healthy tang is decidedly well-rounded. Pinched in, narrow profile individuals should be left in the ocean, or dealer's tanks. Too many times the "reason" (cynical quotation marks mine) for hollow head and flankedness is tied directly with how long the specimens have been starved since capture. This should be days, not the ofttimes weeks in reality. Don't buy skinny marines period.
Feeding and general behavior; healthy, well-adjusted (yep, a psychological term) surgeons are active, curious, anxious eaters on most foodstuffs. Seek out fish that are cruising about, interested in what's going on around them, sampling what have you as food.
Source location: most palette tangs are collected in the vast waters of the Philippine and Indonesian Islands; these have not proven to be the better specimens. For what it's worth (and it does cost more, and is well justified), Paracanthurus hailing from New Caledonia, Christmas, Fiji and Marshall Islands et al. are superior. How to tell where yours is coming from? There's always taking a gander at your dealer's invoice; and a skilled eye can discern the more robust, better colored specimens from these "other" locales. My advice; pay the extra to get better livestock; encouraging better capture, holding and shipping practices elsewhere.
Color; mentioned here as a criterion to not select by. These fish do change intensity with stress and mood; but quickly and unreliably. Besides, there are subtle to larger color and marking differences with locality and size that are hard to elucidate.
Collecting Your Own
Nowhere is the palette surgeon in great abundance, but I have collected them in Guam, Indonesia and the Philippines in the following fashion. Large individuals usually are solitary, smaller one's may be found associated in a group of ten or twenty in and around a large coral head or black coral stand that they take refuge in on a divers approach. A type of net termed a fence, mist or barrier is set up ten to thirty feet away in a U-shape. A retreat away from the area with the holed-up Paracanthurus is feigned and the specimens are chased and pressed against the fence net on showing signs of leaving their coral nest.
Talk about a paradox; the palette tang does best in a well-established system, one that's been up for a few months; but requires "bright" clean water, devoid of measurable organics. How do you get and keep this mystical "high water quality"? Two words; filtration and maintenance.
Circulation itself should be turbulent; the more motion in the water the better. Surgeons appreciate high oxygen gas concentration. An efficient protein skimmer (if possible with an ozonizer) is absolutely necessary; as is over-sized biological and chemical filtration. There should be no detectable color to your water (test some in a tall glass against a white piece of paper, compared with a sample of tapwater).
Paracanthurus may be easily mixed with others of their own kind and any other fishes that will leave them be. They are best exhibited in large (hundreds of gallon) systems with vertical groupings or walls of rock and coral skeletons to provide refuge.
The palette surgeon gets my vote as the least territorial member of its family. Though they will "posture" and "shake their caudal spine" in a threatening way to challengers to their favored hiding or swimming route, Paracanthurus are wont to actually inflict any real damage to conspecifics or other tankmates.
This is one of those species that are better off not being purposely quarantined; put another way, IMO (in my opinion), the stress induced via isolation and re-moving Paracanthurus is generally more harmful than the risk of introduction of some contagion. I would run newcomers through a preventative bath/dip of pH adjusted freshwater and promptly place them in the main/display unit.
To alleviate within-species aggression, if you intend to keep more than one, it is best to introduce all palette tangs at the same time. If need be, make later additions larger than extant members.
Other than small, i.e. planktonic invertebrates and algae, Paracanthurus leave other aquatic life alone. There are other fishes that pester them to distraction though. Be wary of "the usual suspects, including other tangs, large basses and angels, triggers... these can bother your palette to non-feeding.
A quick note here concerning this species propensity for lying on its side, and sidewise "glancing" against the systems substrate. This sort of behavior is natural and to be expected. Do be on the look out for external parasitic problems should yours seem to "scratch too much", and if need be, move the item your tang seems "stuck in" rather than attempt extricating it.
Feeding/Foods/Nutrition: Types, Frequency, Amount, Wastes
Stomach contents analysis of wild Paracanthurus show that this fish is omnivorous, consuming benthic and planktivorous invertebrates and attached algae. Aquarium diets need be diverse, fresh and encompass some nutritious "green" material on a daily basis.
Further, your close watch to ascertain that your palette(s) are eating is called for. As feeders they can be driven away by bullying tankmates, and sulk away to dangerous thinness. In my estimation, a lack of nutrition and outright food are the key reasons for loss of these fish.
This is the darkest element to keeping the palette tang. Paracanthurus are quite susceptible to crypt, (amyl)oodinium, and other infectious and parasitic outbreaks common to captive marines. They are particularly liable to an erosive condition termed HLLE, "head and lateral line erosion". There is growing evidence that this symptom of this bilateral gross pitting and bodily disfigurement is principally due to a lack of nutrients, mainly the vitamins C, A and D; but there are still advocates that a/the root cause of HLLE is stray voltage, and/or the protozoan Octomita necatrix, and/or "poor water quality".
It is my anecdotally derived opinion that all these factors play their part in the expression of HLLE. Given that the species is inclined genetically to this disposition, resolve to keep yours well-fed, in an appropriately set-up and maintained system. Avoid specimens showing signs of erosion as young, and don't give up should yours start to fade and show signs of pitting. Enriched foods and improved conditions have shown to reverse such trends.
The many-named blue tang, Paracanthurus hepatus makes an excellent aquarium fish; active, gorgeously beautiful and long-lived: stipulated that you provide,
1) A stable optimized environment; particularly high water quality and brisk circulation.
2) Foods, including some greenery daily, and evidence that the fish is amply feeding.
3) Selecting healthy specimens; perhaps the most obvious, yet often missing link in keeping these fish alive.
With the permission of Robert (Bob) Fenner webmaster of WetWebMedia ) Photos: top photo by G.J.Reclos; other photos by Stavros Tsipas