Vibration measurements of the perch saccular otolith

Abstract

1. The vertical movement of different parts of the perch saccular otolith was measured with a laser vibrometer during horizontal vibration of the fish back and forth along its long axis. Data were obtained at four different frequencies within the audible range of the fish. Vibration at these frequencies caused very little vertical movement of the skull. 2. No vertical oscillations of the otolith were detected at 20 Hz, whereas both ends of the otolith showed vertical vibrations at 40, 90 and 220 Hz. An area of minimum vertical movement appeared around the midpoint of the otolith at these frequencies, thus indicating the existence of a horizontal axis of rotation. 3. It is argued that the stimulation technique is a reasonable approximation to underwater sound exposure. The measurements thus support the idea of a coarse, peripheral frequency analysis in fish based on a frequency dependent pattern of sound induced otolith movements.