Abstract
BackgroundHearing thresholds of fishes are typically acquired under laboratory conditions. This does not reflect the situation in natural habitats, where ambient noise may mask their hearing sensitivities. In the current study we investigate hearing in terms of sound pressure (SPL) and particle acceleration levels (PAL) of two cichlid species within the naturally occurring range of noise levels. This enabled us to determine whether species with and without hearing specializations are differently affected by noise.Methodology/Principal FindingsWe investigated auditory sensitivities in the orange chromide Etroplus maculatus, which possesses anterior swim bladder extensions, and the slender lionhead cichlid Steatocranus tinanti, in which the swim bladder is much smaller and lacks extensions. E. maculatus was tested between 0.2 and 3kHz and S. tinanti between 0.1 and 0.5 kHz using the auditory evoked potential (AEP) recording technique. In both species, SPL and PAL audiograms were determined in the presence of quiet laboratory conditions (baseline) and continuous white noise of 110 and 130 dB RMS. Baseline thresholds showed greatest hearing sensitivity around 0.5 kHz (SPL) and 0.2 kHz (PAL) in E. maculatus and 0.2 kHz in S. tinanti. White noise of 110 dB elevated the thresholds by 0–11 dB (SPL) and 7–11 dB (PAL) in E. maculatus and by 1–2 dB (SPL) and by 1–4 dB (PAL) in S. tinanti. White noise of 130 dB elevated hearing thresholds by 13–29 dB (SPL) and 26–32 dB (PAL) in E. maculatus and 6–16 dB (SPL) and 6–19 dB (PAL) in S. tinanti.ConclusionsOur data showed for the first time for SPL and PAL thresholds that the specialized species was masked by different noise regimes at almost all frequencies, whereas the non-specialized species was much less affected. This indicates that noise can limit sound detection and acoustic orientation differently within a single fish family.
Highlights
The auditory sensitivity of fishes has been measured in more than 150 species covering a large number of families, hearing sensitivities and habitats
Our data showed for the first time for SPL and particle acceleration levels (PAL) thresholds that the specialized species was masked by different noise regimes at almost all frequencies, whereas the non-specialized species was much less affected
The natural environment of marine and freshwater fishes is characterized by a permanent background noise of abiotic, biotic and increasingly anthropogenic origin. These factors result in a large diversity of ambient noise levels and spectra, which have been characterized recently in a few studies [3,4,5,6,7,8,9,10,11,12]
Summary
The auditory sensitivity of fishes has been measured in more than 150 species covering a large number of families, hearing sensitivities and habitats. The natural environment of marine and freshwater fishes is characterized by a permanent background noise of abiotic (currents, rain, wind, tides, coastal surf), biotic (vocalizations of animals, underwater movements of plants such as reeds) and increasingly anthropogenic origin (ships and boats, hydrodynamic power plants, seismic exploration) These factors result in a large diversity of ambient noise levels and spectra, which have been characterized recently in a few studies [3,4,5,6,7,8,9,10,11,12]. In the current study we investigate hearing in terms of sound pressure (SPL) and particle acceleration levels (PAL) of two cichlid species within the naturally occurring range of noise levels This enabled us to determine whether species with and without hearing specializations are differently affected by noise
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