#redspot surgeonfish

[i-give-you-a-fish]

Goth fibsh?

Greacher

You get an Achilles Tang

Acanthurus achilles

[aquariuminfobureau]

The Achilles tang, Acanthurus achilles, which is also known as the redtail or redspot surgeonfish, is but one of the many surgeonfish or acanthurid species that dwell on the tropical reef, and nearby in reef associated habitats. Specifically the Achilles tang has quite a broad Pacific distribution, within which it is found on the seaward side of coral reefs in crystal clear, turbulent water, strongly affected by wave action. Contrary to much information that is aimed at aquarists, this species naturally congregates in conspecific groups. A large member of A. achilles may be up to 24 centimeters or nearly 10 inches long, but much more commonly they are a little smaller, reaching 20 centimeters or 8 inches long.

Despite being sought after by aquarists, A. achilles are often injured by improper handling during capture methods. Such treatment is not only stressful, but also ultimately lethal in many cases. As a result this species has gained a reputation as very difficult to care for, although care by retailers and home aquarists, is not the source of their delayed mortalities. Other than the effects of poor ethics and maltreatment, the only cautions surrounding A. achilles, are the usual caveats with acanthurid fishes, or those organisms from seaward reefs with pristine water. Acanthurids are susceptible, as a group, to attack by the burrowing, unicellular endoparasites that are responsible for white spot and velvet diseases, and treating these maladies in the presence of corals can be problematic.

Acanthurids, the group of fishes also known as surgeonfishes or tangs, are among the important algivorous fishes found in shallow, tropical seas. Other than a few ecological outliers,the acanthurids, and their closest relatives, are either browsers or grazers, and the species naturally vary as to how strictly vegetarian they actually are. A technique called DNA barcoding has identified A. achilles as strictly herbivorous in the wild, and together with existing field observations of their feeding, and comparisons of the shape of their teeth, it is confirmed that this species are best categorized as vegetarian browsers.

The habit of browsing fishes is to nip at fleshy or foliate organisms, which invites analogy with land organisms. Browsing land animals such as deer and giraffes, are those that selectively take advantage of food growing high up, whereas grazers such as zebra, wildebeest, and buffalo crop less discriminately at food very close to the substrate. In the sea, not only plant life but sessile animals are aptly described as subject to grazing and browsing 'predation'. Naturally it is grazing fish that are more likely to damage small polyps, and those colonies with encrusting or plate forming habits, either deliberately or incidentally. Whilst browsers will more likely assail sessile organisms that are fleshy or possess a frondose growth.

Of course A. achilles, being a strict herbivore, is browsing on macroalgae with a frondose or fleshy growth habit, rather than feeding on filamentous algae or microalgae, as some other, often related fish prefer. This species specifically nips at fleshy macroalgae in the wild, and I have heard anecdotes that they can attack Tridacna sp. mantles, which are as fleshy as their natural diet. However A. achilles have no inclination to attack the prized Acropora corals, which share similar requirements to A. achilles regarding water parameters. I would not trust them entirely with any corals bearing a fleshy appearance, but A. achilles is one of the most coral friendly of the Acanthurus species.

In the aquarium A. achilles should be fed mainly on marine vegetables. Acanthurids will also accept prepared foods rich in Spirulina, and vegetables such as courgette or blanched, dark lettuce. As active fish, A. achilles require swimming space, and in reflection of their origins, they need to live in clear and oxygenated water. Although A. achilles has a reputation as extremely aggressive, it does not seem exceptional. Confrontations are usually limited to other acanthurids, and the related siganid species. It would seem that the personalities of individual fishes in this group determine their aggression. Despite naysayers, I have seen more than one mature A. achilles, of similar size, sharing a large aquarium with similar fishes.

Acanthurids obtain their name of 'thorntails' and their vernacular name of surgeonfishes, from the sharp, retractable blades that Acanthurus sp. and its close allies possess. This distinguishes acanthurids from the idols and siganids that do not possess them, and those of basal acanthurids are not foldable. These switchblades on their tails are modified, weaponized scales that can injure a human handler, and damage nets. It is not yet known wether these blades are toxic, but it is strongly suspected that they are in at least some acanthurid species. Either way, it is the presence of these fighting instruments that makes aggression by acanthurids a potential, sometimes deadly problem in the aquarium.