Juvenile Pareques acuminatus (Peter Leahy / shutterstock.com)

The drumfish (Scianidae), also called drum or croaker, has a long dorsal fin with a deep notch between the spinous and soft portion. Drumfish use their swim bladder as resonance chamber for producing drumming sounds. The largest species (Totoaba macdonaldi) can grow up to 2 meters (6.6 feet) in length and 100 kilograms (220 pounds) in weight. However, most species are much smaller.

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