Structural Diversity in the Inner Ear of Teleost Fishes: Implications for Connections to the Mauthner Cell

A body of literature suggests that the Mauthner cell startle response can be elicited by stimulation of the ear. While we know that there are projections to the M-cell from the ear, the specific endorgan(s) of the ear projecting to the M-cell are not known. Moreover, there are many reasons to question whether there is one pattern of inner ear to M-cell connection or whether the endorgan(s) projection to the M-cell varies in species that have different hearing capabilities of hearing structures. In this paper, we briefly review the structure of fish ears, with an emphasis on structural regionalization within the ear. We also review the central projections of the ear, along with a discussion of the limited data on projections to the M-cell

Evaluation of Evidence for Altered Behavior and Auditory Deficits in Fishes Due to Human-Generated Noise Sources

In this study, we have evaluated peer-reviewed publications and contracted reports to provide an overview of what is known about auditory processing by fishes and the behavioral and physiological effects of various noise stimuli as documented by the best and most appropriate studies. We include reviews of work on both cartilaginous (sharks, skates, and rays) and teleost fishes (modern bony fishes) and provide recommendations for research to address remaining issues. Clear responses to human-generated noise have been documented in several marine species of interest. Sharks may be attracted to low-frequency pulsed sounds, which can change their normal distributions and could increase agonistic interactions between individuals and/or species. However, sharks also learn to ignore sounds that are not associated with food, so that any change in distribution or local density should return to normal levels eventually. There are no studies that show long-term avoidance of an ensonified area, even though a shark may exhibit a startle response at the onset of a sudden loud noise. Teleost fishes also have specific behavioral responses to some human-generated noise, in particular to seismic surveys and ship noise. The responses range from brief interruptions i

Physiological evidence for binaural directional computations in the brainstem of the oyster toadfish, Opsanus tau (L.)

Comparisons of left and right auditory input are required for sound source localization in most terrestrial vertebrates. Previous physiological and neuroanatomical studies have indicated that binaural convergence is present in the ascending auditory system of the toadfish. In this study, we introduce a new technique, otolith tipping, to reversibly alter directional auditory input to the central nervous system of a fish. The normal directional response pattern (DRP) was recorded extracellularly for auditory cells in the first-order descending octaval nucleus (DON) or the midbrain torus semicircularis (TS) using particle motion stimuli in the horizontal and mid-sagittal planes. The same stimuli were used during tipping of the saccular otolith to evaluate changes in the DRPs. Post-tipping DRPs were generated and compared with the pre-tipping DRPs to ensure that the data had been collected consistently from the same unit. In the DON, ipsilateral or contralateral tipping most often eliminated spike activity, but changes in spike rate (±) and DRP shape were also documented. In the TS, tipping most often caused a change in spike rate (±) and altered the shape or best axis of the DRP. The data indicate that there are complex interactions of excitatory and inhibitory inputs in the DON and TS resulting from the convergence of binaural inputs. As in anurans, but unlike other terrestrial vertebrates, binaural processing associated with encoding the direction of a sound source begins in the first-order auditory nucleus of this teleost