Powder blue surgeonfish (Jon Connell / CC BY)

The surgeonfish (Acanthuridae) has an oval, brightly colored body and characteristic scalpel-like caudal spines. Its continuous dorsal and anal fins are relatively long. Its mouth is small and has a single row of teeth. Surgeonfish species range from 13 centimeters (5 inches, pale-tailed bristletooth) to 1 meter (39 inches, whitemargin unicornfish) in length. If provoked, surgeonfish may use their razor-sharp caudal spines, which can inflict nasty cuts, in self-defense.

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This supplemental online resource accompanies the book Scuba Diving Hand Signals by Lars Behnke, available on Amazon.