Nerve Fibre and Receptor Counts in the Sprat Utriculus and Lateral Line

Abstract

INTRODUCTIONIt has long been known that the ears of clupeoid fishes differ from most other fish in that they have a gas-containing bony bulla associated with each ear (for references to early work see Allen, Blaxter & Denton, 1976). The expansion and contraction, with changing pressure, of this gas causes liquid to flow in the ear and lateral line (Gray & Denton, 1979; Denton, Gray & Blaxter, 1979) thus causing displacements (Best & Gray, 1980) and excitation (Denton & Gray, 1980) of the utricular maculae; it also causes excitation of the lateral line neuromasts (unpublished). Only a small fraction of the alternating liquid flow from the bullae passes through the pars inferior of the labyrinth (Gray & Denton, 1979). Furthermore, in larvae, when the utricular structures can be seen to move vigorously with an alternating pressure the saccular otolith is not seen to move (Blaxter, Denton & Gray, 1981).