Directional hearing in the goldfish ( Carassius Auratus )

Directional hearing in fish is a complex, ambiguous, and poorly understood phenomenon. Some nonostariophysian fish, particularly the cod, have shown the ability to unambiguously determine the direction of a monopole sound source and that their angular resolution is perhaps as good as 10°. Although considered ‘‘hearing specialists,’’ there is little evidence that ostariophysian fish are capable of directional hearing. An attempt to classically condition the ostariophysian goldfish to discriminate sound sources differing only in location failed. The sound signal was pulsed bandpass filtered noise at least 20 dB above previously determined sound pressure masked thresholds. Ostariophysian fish are characterized by the presence of Weberian ossicles, coupling the air filled swim bladder to the inner ears. This may enhance pressure sensitivity at the expense of directionality. This apparent lack of directional hearing capability will be examined in light of the known ability of goldfish to show directionality in their Mauthner mediated acoustic startle response and the physiological data demonstrating directionality in the individual auditory end organs. [Research supported by ONR.]