Effects of Intense Sounds on the Ear of Fishes

Over the past several years there has been considerable interest generated in the impact of human-generated (anthropogenic) sounds on the ears of animals. It is widely known that intense sounds and certain drugs will damage the sensory cells of the ears of mammalian species, and the concern is that similar sounds will impair hearing in wild animals. Related to this is the increase in the presence of anthropogenic sounds in the environment. This has been of particular interest for its impact on marine mammals, where the concern is that human-generated sounds from a variety of underwater activities may impair the survival of a number of species (see NRC 2000).

While the major interest in the impact of anthropogenic sounds in the marine environment concerns mammals, it is now appreciated that these sounds may also impact the lives of fishes and other organisms as well as marine mammals. However, the extent of data on the effects of intense sounds on fishes is only poorly known. At the same time, several results from the Popper lab are germane to the topic.

One of the very few direct studies on the impact of intense sounds on the ear of fishes was done in collaboration between the Popper lab and the lab of Dr. Mardi Hastings at the Ohio State University. In this study (Hastings, M.C., Popper, A.N., Finneran, J.J., and Lanford, P.J. (1996). Effect of low frequency underwater sound on hair cells of the inner ear and lateral line of the teleost fish Astronotus ocellatus. J. Acoust. Soc. Am. 99:1759-1766.) we investigated the effect of high intensity on the ears of the oscar, Astronotus oscellatus. We found that sounds that were lower than 180 dB (re 1 µPa) and sounds that were not on continuously had no apparent impact on the sensory cells of the ear. However, when we subjected fish to 180 dB signals 300-Hz pure tones for four continuous hours, and then examined the ears after four days, there was some damage to the sensory cells of the lagena. This is shown in the figure to the right. In this scanning electron micrograph from the lagena, the top figure shows a low power view of the whole macula. The area within the square is shown in the lower SEM. The lower picture shows that there has been some loss of ciliary bundles resulting from the high acoustic stimulation.

While damage was found in a number of specimens, it did not show up unless the animals were allowed to live for several days, suggesting that damage takes a while to be visible. While these data are highly suggestive that damage may result from long-term intense sounds, there are several caveats on these data. First, it is not known if data from this freshwater fish can be extrapolated to other species. Second, how significant is this damage in terms of sound detection, and would damage of this low magnitude impact the survival of a fish? Third, it is important to note that the fish in this study were kept close to the sound source, and it is unlikely that fish in the wild would be exposed to four-hours of continuous sound and stay in the vicinity of the sound for the full time. Another significant question is whether the hair cells that are damaged would regenerate. As we have shown in other studies, sensory cells in the ears of fish do regenerate after treatment with ototoxic drugs, and this might mean that the hair cells in fishes would also regenerate after damage by intense sounds. Thus, while there may be some damage shortly after sound stimulation, will this have a long-term impact on fish? Of course, during the time that damage is present, and before any regeneration, fishes may be at a disadvantage in terms of detecting predators and prey, and so their survival may be impacted.

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