Unicornfish
Spotted unicornfish (Derek Keats / CC BY)
Unicornfish (Naso sp.) are relatively large members of the surgeonfish family. The unicornfish is named for a protruding spike or bulbous on its forehead that develops with age. Like other surgeonfish, unicornfish usually have razor-sharp spines near their tail fins, which they also use in self-defense. The whitemargin unicornfish can grow up to 1 meter (39 inches) in length.
This supplemental online resource accompanies the book Scuba Diving Hand Signals by Lars Behnke, available on
Amazon.