Acanthurus chirurgus
Doctorfish [+]
Description & Behavior
The doctorfish, Acanthurus chirurgus (Bloch, 1787), gets its name from a small, sharp spine-like structure that lies along each side of the caudal peduncle. This is referred to as a "scalpel", and is as sharp as its name suggests. It is said to be used during fights with other fish for dominance and for defense against predators. The doctorfish reaches lengths of 39 cm, weighs up to 5.1 kg, and can vary slightly in its overall color. It can change from blue-gray to dark brown, and pale or darken dramatically. It has from 10-12 thin, dark, vertical bars visible on the sides. These bars separate the doctorfish from other regional Acanthurus species like the blue tang and other surgeonfish. There is a faint blue ring that encircles the scalpel on each side. The edges of the anal, dorsal, and caudal fins are blue, regardless of the body color.
World Range & Habitat
The doctorfish lives in shallow areas of reef or rocky habitats. It is the most wide-ranging of the species of the surgeonfishes, Acanthurus, in the Atlantic and is found from Massachusetts to Brazil, including the northern Gulf of Mexico and the Caribbean. It can also be found along the tropical western coast of Africa.
Feeding Behavior (Ecology)
The doctorfish is a daytime grazer, feeding on mostly algae and organic detritus. Its teeth, specialized for scraping algae, are spatula-like in shape, close together, and notched on the edges. Since the fish swallows its food whole, it must depend on a unique adaptation for breaking up the food into smaller pieces. It has a gizzard-like organ in the intestine that is partially filled with sand particles. This organ apparently helps the fish to grind up food prior to digestion.
Life History
Doctorfish spawning is a group event 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/Additional Comments
An unwary human who tries to handle the doctorfish risks the chances of being badly cut by its scalpel. The flesh is of good quality, but is not highly valued in most places.
References & Further Research
BioOne ~ CITES ~ Discover Life ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList ~ MarineBio Network ~ NCBI ~ SCIRIS ~ SIRIS ~ Tree of Life Web Project ~ Wikipedia
Florida Museum of Natural History
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