Acoustical stress and hearing sensitivity in fishes: does the linear threshold shift hypothesis hold water?

Abstract

SUMMARY Mammals exposed to loud aerial sounds exhibit temporary threshold shifts(TTS) that are linearly related to increases of sound pressure above baseline hearing levels. It was unknown if this relationship held true for aquatic ectotherms such as fishes. To test this linear threshold shift hypothesis(LINTS) in fishes, we examined the effects of increased ambient sound on hearing of two species differing in hearing capabilities: goldfish(Carassius auratus; a hearing specialist) and tilapia(Oreochromis niloticus; a hearing generalist). Fish were exposed to 1–28 days of either quiet (110 dB re 1 μPa) or continuous white noise. First, we examined the effect of noise sound pressure level (SPL; 130,140, 160 or 170 dB re 1 μPa) on goldfish hearing thresholds after 24 h of noise exposure. Second, in a long-term experiment using 170 dB re 1 μPa white noise, we continuously exposed goldfish and tilapia for either 7 or 21–28 days. In both experiments, we measured alterations in hearing capabilities (using auditory brainstem responses) of noise-exposed fish. While tilapia exposed to noise for 28 days showed little or no hearing loss,goldfish exhibited considerable threshold shifts that reached an asymptote of up to 25 dB after only 24 h of exposure. There was a positive linear relationship between noise-induced TTS and the sound pressure difference between the noise and the baseline hearing thresholds in goldfish but not in tilapia. A similar relationship was found for published noise-induced threshold shifts in birds and mammals, but the slope of the linear relationship was greater in these groups than for fish. The linear threshold shift relationship provides insights into differential susceptibility of hearing specialist and generalist fishes to noise-induced hearing loss for a given SPL and provides a framework for future research on noise-induced threshold shifts in fishes and other animals.

Potential mechanism of sound production in Oreochromis niloticus(Cichlidae)

“…The backward displacement of the pectoral girdle should involve a backward and ventral displacement of the lower pharyngeal jaws, preventing the lower pharyngeal jaw from coming into contact with the upper pharyngeal jaws. Furthermore, O. niloticus should not be able to hear sounds resulting from tooth stridulation because they do not seem able to hear sounds above 2000Hz (Smith et al, 2004). A hydrodynamic sound production mechanism would seem plausible, because hydrodynamic sounds are usually produced by axial muscles (Shishkova, 1958;Moulton, 1960), but the fact that O. niloticus sounds are audible in air rules out this hypothesis.…”

Broadband noise exposure does not affect hearing sensitivity in big brown bats (Eptesicus fuscus)

“…Cumulative short duration exposures or long duration exposures of days to weeks produce permanent threshold shifts from which recovery does not fully occur (Clark, 1991). These impairments have been documented in many vertebrate species, including fishes (Amoser and Ladich, 2003;Smith et al, 2004), birds (Ryals et al, 1999), rodents (Ryan and Bone, 1978;Boettcher, 1993;Heffner et al, 2008), marine mammals (Popov et al, 2013;Finneran, 2015) and humans (Ward et al, 1958;Mills et al, 1981). In spite of species and individual differences in the most effective acoustic parameters for producing TTS, these animals all demonstrate some hearing losses under some exposure conditions.…”

“…Comparative analyses (Smith et al, 2004) suggest that mammals are more susceptible to TTS than are fishes or birds. Among mammals, however, differences in the magnitude of threshold shifts after noise trauma have been observed, even under similar exposure conditions.…”

Anatomical and functional recovery of the goldfish (Carassius auratus) ear following noise exposure

“…Exposure to broadband noise can cause temporary threshold shifts (TTS) in goldfish (Carassius auratus) and catfish (Pimelodus pictus), both otophysan fishes with relatively sensitive hearing thresholds (Amoser and Ladich, 2003;Smith et al, 2004a;Smith et al, 2004b). Fishes with less sensitive hearing do not appear to be as susceptible to TTS under identical conditions (Scholik and Yan, 2002;Smith et al, 2004a), although exposure to much more intense sounds produced by a seismic air gun does produce TTS in at least some non-otophysan fishes (Popper et al, 2005).…”