Doctorfishes, Acanthurus chirurgus
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Description & Behavior
Doctorfishes, Acanthurus chirurgus (Bloch, 1787), aka doctor fishes, black doctorfishes or doctorfish tangs, who get their name from a small, sharp spine-like structures that lies along each side of their caudal peduncle (area just forward of the tail fin). These are referred to as "scalpels", and are as sharp as their name suggests. It is said to be used during fights with other fish for dominance and for defense against predators. Doctorfishes reach lengths of 39 cm, weigh up to 5.1 kg, and can vary slightly in overall color. They can change from blue-gray to dark brown, and pale or darken dramatically. They have 10-12 thin, dark, vertical bars visible on their sides. These bars separate the doctorfish from other regional Acanthurus species like the blue tang and other surgeonfishes. They also have a faint blue ring that encircles the scalpel on each side of their tails. The edges of the anal, dorsal, and caudal (tail) fins are blue, regardless of the body color.
There is also a genetic variant of the doctorfish tang that is colored black though it is not reportedly a subspecies or a regional mutation and has been rarely been seen.
World Range & Habitat
Doctorfishes live in shallow areas of reef or rocky habitats at depth ranges of 2 - 25 m though usually above 15 m. They are common and the most wide-ranging of the species of the surgeonfishes, Acanthurus (38 species), in the Atlantic and is found from Massachusetts to Brazil, including the northern Gulf of Mexico and the Caribbean. They can also be found along the tropical western coast of Africa (Senegal). Subtropical: 22° C - 25° C; 37° N - 7° S, 89° W - 34° W
Feeding Behavior (Ecology)
Doctorfishes are daytime grazers, using feeding on algae. Their teeth are specialized for scraping algae, being spatula or spade-like in shape, close together, and notched on the edges. Since these fish swallow their food whole, they also ingest sand and depend upon a gizzard-like organ in their intestines to help these fish grind up their food prior to digestion.
At Fernando de Noronha Archipelago in the southwestern Atlantic Ocean, juvenile doctorfishes are found at "cleaning stations" with the blue tangs and sergeant majors and graze algae as well as pick molted skin and parasites from green sea turtles.
Doctorfishes spawn in group events that occurs during evening hours. The eggs are small, less than a millimeter in diameter. The eggs are pelagic, each containing a single droplet of oil for flotation. The eggs hatch in twenty-four hours into small, planktonic, translucent larvae. The newly hatched larva is diamond-shaped and laterally compressed, with a head shaped like a triangle. It has large eyes and prominent pectoral fins. The dorsal fins, anal fins, and scales begin to develop when the larva reaches 2-6 mm in length. The scalpel does not appear until the larva reaches about 13 mm in length. Late post-larvae drift inshore, where they change into juveniles. The larvae lose their silver color and turn brown. Their profiles become round. The prominent dorsal and anal spines that are characteristic to the larvae reduce, while the scalpel gets bigger. Complete metamorphosis takes about a week, after which 2.5 cm long juveniles settle onto the bottom. Juveniles grow rapidly, attaining sexual maturity in as little as nine months.
Conservation Status & Comments
An unwary human who tries to handle a doctorfish risks the chances of being badly cut by its scalpels.
References & Further Research
Research Acanthurus chirurgus » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
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