I Didn’t Know That

Q: Fish don’t appear to have ears. Do they hear sounds?

A: Fish definitely do have ears, although they are not readily visible, said Ken Yates, vice president for husbandry at the Aquarium of the Pacific in Long Beach. These inner ears, like those of humans, also help fish maintain their balance. The ears contain dense bones, called otoliths, that work almost the exact opposite of the way human ears work. When a fish is exposed to sound waves, its whole body vibrates with the waves. The dense otolith, however, vibrates more slowly, lagging behind the body’s vibrations. It is this lag that the fish’s brain interprets as sound. Fish also sense sounds through the so-called lateral lines along the sides of their bodies, and the gas bladder in some species can also help transmit sound.

Otoliths grow a little bit larger each year as new bone condenses on their surface, producing rings much like the rings on a tree. These rings can be used to determine the age of a fish at its death.