Directional Sensitivity of Saccular Microphonic Potentials in the Haddock

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Abstract
Microphonic potentials from the sacculus in the haddock have been recorded by implanted electrodes during horizontal vibration of the fish in air. This gives a good simulation of sound stimulation in water. The microphonic potential amplitude was a function of the vibration angle, and from most recording loci maximal amplitudes were obtained for vibration directions parallel to the long axis of the fish. The sensory cells contributing to this response are therefore most sensitive to displacements in the same direction as sound-induced swimbladder pulsations would produce. This result thus supports the theory of an accessory role of the swimbladder in sound reception. Highest sensitivity to vibration directions other than parallel to the long axis of the fish has been obtained from other recording loci. One example of highest sensitivity to a vibration direction at right angle to the long axis of the fish is presented. The findings that different sensory cells appear to have different axes of maximal sensitivity to vibration provides one possible neurological explanation for the ability of fish to detect the direction to a sound source.