A nerve ending, called a cupula extends into each canal. Any angular movement of the fish would induce relative motion in the fluid, bending the cupula and stimulating the nerve. The orientation relative to gravity will determine which nerve endings the otolith contacts. Sound Most fish tissues are similar in density to water and thus transparent to sound waves. Vibration of the otoliths permits detection of low frequency sounds.
Most fish have irregularly-shaped otoliths.
Many fish are capable of producing sounds. These are usually low-pitched, grunt like noises produced by grinding together pharyngeal teeth or movement of a muscle layer against the swimbladder. Sounds may be used for orientation and keeping together in a loosely feeding group, for sexual or species recognition, or for warning. The lateral line system consists of bendable nerve endings in a series of mucous-filled canals Vibrations in the water or differential pressure in different parts of the canal cause the fluid to move and distort the nerve endings. Because of it's name, we think of the lateral-line system as being oriented laterally on the fish.