A model for the nearfield acoustics of the fish swimbladder and its relevance for directional hearing.

It is a well-known fact that fish can determine the direction of an underwater sound source. For bony fish without Weberian ossicles the mechanism proposed here is the analysis of the elliptical movement of the otolith macula relative to the otolith in case a pure tone is emitted. This movement results from the superposition of the direct displacement wave and the displacement wave scattered by the swimbladder acting as a damped harmonic oscillator. A derivation of a closed analytical expression of the scattered wave is given for a prolate spheroidal air bubble (representing the swimbladder) in water. The elliptical displacement orbits of the surrounding medium were calculated. A general numerical approach is given for irregular gas bodies.