Abstract:
Both the lateral line and the inner ear contribute to near field dipole source detection in fish. The precise roles these two sensory modalities provide in extracting information about the local flow field remains a topic of interest. In this study, Acoustico-lateralis evoked potential (ALEP) thresholds (30-200 Hz) were measured in response to a dipole source for two morphologically different species, the blind cavefish and the common triplefin. To test the contribution of the lateral line, we measured the effects of the drug neomycin trisulfate on threshold sensitivity and amplitude of the ALEP for both species in response to a 40 Hz dipole stimulus. To test the efficacy of neomycin as a tool for lateral line ablation, DASPEI (2-[4-(dimethylamino)styryl]-N-ethylpyridinium iodide) vital dye was used to verify neuromast hair cell death in the blind cavefish. When plotted in terms of acceleration, threshold curves for both species showed greatest sensitivity at the lowest frequency tested. The common triplefins were more sensitive to particle acceleration than blind cavefish at all frequencies tested. Treatment with the drug neomycin caused a significant decrease in the peak-to-peak amplitude of the ALEP in common triplefins within the first 30 min and increased the threshold sensitivity by an average of 10.8 dB after 4 h. No significant effect of treatment was observed in the blind cavefish, however, DASPEI results confirmed that neuromast hair cell death was significant in treated fish. These results indicate that, under the conditions of this experiment, sound pressure detection by the inner ear is important for dipole detection by the blind cavefish, but that incompressible flow detection by the lateral line is more important for the common triplefin. The results from this study imply that the loss of lateral line function can be compensated for via detection of the pressure component of the vibration source in fish possessing a swim bladder.
