Sounds fish hear and the importance of hearing to fish have been matters of much conjecture and many misunderstandings. What we do know is that underwater, sound is transmitted almost five times faster than in air and may be perceived over longer distances. Underwater sound, therefore, can be a sensory tool for anglers.

A recent scientific summary by Arthur Popper and Thomas Carlson** provides updated information on the relationship between underwater sound and fish hearing. Some of this information, previously covered by scientific reports, is given as a review, along with new data on hearing in gamefish.

Underwater Sound

Underwater sound is a density disturbance that propagates through water at a speed independent of the sound frequency, with amplitude decreasing in proportion to distance from the source. In water, sound travels at slightly less than a mile per second. It slowly fades, is highly directional, and is not impeded by low light levels or turbidity. Thus, sound can be an important reference to help gamefish orient within their environment, to warn of threats, and to help locate prey.

Sounds are weakened by mechanical and chemical factors as well as by distance. Underwater structures or cover between a sound source and a fish can block sound. Also, dense layers of thermoclines may reflect or misdirect sounds. Sounds weaken as frequency increases, so high-pitched sounds fade faster than low-pitched sounds.

The energy of a sound wave in water is contained in the local back-and-forth movements of water particles and associated changes in water pressure. The particles have direction, and this direction along with pressure change is sensed by fish. In air, particle motion is quickly lost, and human hearing doesn’t rely on it. In water, however, particle motion is a significant part of sound production, and fish have evolved to use it. But particle motion degrades more rapidly than pressure waves. It’s important, therefore, to know how well each fish species can detect particle displacement with their ears and lateral lines to estimate which noises are heard and which aren’t.

Unfortunately, few published studies are available on the specific range, frequency, and hearing characteristics of gamefish. Until these studies are made, anglers and lure manufacturers are limited to using angling successes and failures as guides.

Hearing & The Lateral Line

Fish have two sound-detection systems—the inner ear and lateral line—that hear or feel both particle motion and pressure changes. As both systems use similar hair cells as detection devices, biologists once believed that the two systems were interrelated and shared functions. Research has shown, however, that the two sensory systems are separate, develop independently, send signals to different areas of a fish’s brain, and perform different functions. Fish hear sounds up to a considerable distance away, while their lateral lines feel only vibrations and pressure changes generated nearby.

Nevertheless, some overlap occurs at low frequencies, defined by the authors as 35 to 300 Hz (hertz—cycles per second). Most fish species hear sounds between about 50 Hz and 1,500 to 2,000 Hz. Lateral lines detect differences between the motion of fish and the motion of the surrounding water between about 1 Hz and about 345 Hz, typically with maximum sensitivity in the range of 10 to 170 Hz.

So moderately low-frequency sounds can be sensed by both systems. A few species sense infrasonic sounds, defined as sounds below 35 Hz. Several species, including carp, cod, shad, alewives, and gar, respond to ultrasonic sounds above 20,000 Hz, though how fish detect sounds of such high frequency is unknown.