Distribution

Tropical and warm seas and oceans (not in the Mediterranean).

Biology

Typical inhabitants of coral reefs, with a high or elongated, egg-shaped body that is laterally oblate. Rabbitfishes, which are also venomous, are closely related to surgeonfishes.

Fig. 4.24 Acanthurus sp. The erectable, razor-sharp spine at the base of the tail is shown in the erect position and slightly enlarged to make it more clearly visible.

Surgeonfishes are very active and almost always in motion. The largest species reach up to 60 cm in length. Many are strikingly brightly coloured and able to change colour.

The characteristic feature that gives this group of fish its name are the spines or erectable "blades" on each side of the base of the tail. In some members of this group, such as the unicorn fishes (Naso spp.), these are bony stumps or fixed, sharp bony spines.

The genera Acanthurus, Ctenochaetus, Paracanthurus and Zebrasoma have sharp, movable blades that are embedded in a skin sheath at the base of the tail when in the resting position (Fig. 4.24). If the fish is under threat, these blades are erected outwards from the posteriorly located articulation. Thus surgeonfishes can use this blade to inflict deep, often fatal gashes by beating their tail when swimming past an attacking fish.

The integument that covers the blade is very thin and poorly developed in some acanthurids. In some of the larger species, however, it is quite thick and equipped with a secretory function. However, it is not clear whether these secretions are toxic.

Juvenile fish of the Sawtail surgeonfish Prionurus microlepidotus are believed to have fin rays equipped with venom glands.

Risk

Accidents are usually the result of carelessness when removing the fish from a fishhook or when sorting fish from fishing nets. It is highly unlikely that these fish would attack humans in the water.

Treatment

Symptomatic.

Literature (biological)

Cameron and Endean 1972, Halstead 1988, Monod 1959, Smith and Heemstra 1986, Tange 1955