Abstract:
Fifty-nine oscars (Astronotus ocellatus) were subjected to pure tones at 60 or 300 Hz in order to determine the effects of sound at levels typical of man-made sources on the sensory epithelia of the ear and the lateral line. Sounds varied in duty cycle (20% or continuous) and sound-pressure level (100, 140, or 180 dB re: 1 (mu)Pa). Fish were allowed to survive for one or four days post-treatment. The study also included five control animals that were handled in the same way as the test animals, but were not exposed to any sound. Tissue was then evaluated using scanning electron microscopy to assess the presence or absence of ciliary bundles on the sensory hair cells in each of the otic endorgans and the lateral line. Damage was found in four of five fish stimulated with 300-Hz continuous tones at 180 dB and allowed to survive for four days. It was limited to small regions of the striola of the utricle and lagena. No damage was observed in fish that had been allowed to survive for one day post-stimulation, suggesting that physical signs of damage may develop slowly after exposure. [Work supported by ONR.]