The otic gasbladder as an ancillary auditory structure in a mormyrid fish

Mormyrid fishes use acoustic signals for long-distance communication and a weakly electric field for short-distance interaction. Mormyrids are unique in having an otic gasbladder attached directly to the saccule on each side of the inner ear. Karl von Frisch (1938) hypothesized that the tightly coup led otic gasbladder might aid mormyrid hearing. Using the mormyrid fish (Br ienomyrus brachyistius), this study manipulated gas in the otic gasbladder to test: this hypothesis and histological sections were made to examine the anatomical relationship between the gasbladder and inner ear. The hearing sensitivity curves (audiograms) were obtained with the auditory brainstem r esponse protocol. Audiograms were obtained from normal fish and from fish i n which gas was withdrawn from either one or two otic gasbladders. Removal of gas from one otic gasbladder did not result in a significant change in e ither hearing ability or acoustically evoked brainwaves as compared to the control fish. Bilateral deflation of the otic gasbladders led to significan t threshold changes. Histological sections revealed a particularly close co upling between the otic gasbladder and the saccule chamber. These results s upport von Frisch's hypothesis that the otic gasbladders of mormyrids assis t in underwater sound detection.