W-Shaped Auditory Threshold Curves of Masu Salmon Oncorhynchus masou.

Abstract

We made experiments to measure the auditory threshold of masu salmon Oncorhynchus mason using conditioning with electric shock, and also to determine the resonance frequency of masu salmon and rainbow trout Oncorhynchus mykiss swim bladders. Then we examined the role of the swim bladder as a sound pressure amplifier and transducer. The auditory threshold curve for masu salmon was W-shaped, with higher thresholds at 300 and 500Hz in the range of 100-700Hz. Masu salmon were less sensitive to sounds of 300-500Hz than to adjacent frequencies. Swim bladders of rainbow trout fully vibrated in the range 300-600Hz, with resonance frequencies around 400Hz. On the other hand, masu salmon's resonance frequencies were not evident. Therefore, the auditory thresholds of masu salmon at 300-500Hz were high because the swim bladders did not vibrate or transduce the sound to the inner ear at that range. It was assumed that the hearing capabilities were influenced by the characteristics of the swim bladder vibration.