Title Basic study for fish auditory brainstem response
Authers Tomohiro SUGA
Keywords fish, auditory threshold, hearing, ABR
Citation Bull. Fish. Res. Agen. No.28, 115-169, 2009
The Auditory brainstem response (ABR) method is an alternative method to measure the fish auditory threshold. The ABR method allows quick and repeatable measurement of fish without invasive surgery. In this work we developed a method to measure audiograms of fishes.
 To date, there is no method available to determine the effect of water displacement on method to measure fish hearing, because the measurement of displacement is quite difficult in an auditory experiment. A well-known method to eliminate water displacement when measuring fish audiograms is to face two loudspeakers towards each other and then place a fish between the speakers. This study describes another method to eliminate water displacement. This method measured audiogram in air. Audiogram of marbled sole Pleuronectes yokohamae obtained in air was higher than those obtained in water. This difference was presumably due to inner ear or lateral line sensitivity to water displacement around the center of the water tank.
 Next we demonstrated that some of the ABR components of fishes are derived from peripheral organs such as the saccule, lagena and utricle in the inner ear. In this experiment, we used sound stimuli of different durations to demonstrate that the ABR of goldfishes Carassius auratus was contaminated with microphonic potential. The durations of the ABR were in proportion with the durations of the sound stimuli.
 Next the ABR of fishes is commonly measured by bringing the heads of the fishes out of the water in a small tank, however this method is inapplicable to experiments for large fishes that are economically important in large space such as the sea or in a large tank. This study describes a method to record the ABR for fishes in water without exposing the fish heads in air using a water proof and insulated electrode. To evaluate the effectiveness of this method, the goldfish was investigated, and the ABR waveform and auditory thresholds measured in water were compared with these measured on the surface. Both ABR waveforms and auditory thresholds showed similar trend between the two methods. The “underwater ABR method” is considered to be useful to measure the larger fish auditory threshold in a natural or on site environment as in the sea, net enclosures and large aquaria in which precise positioning of the fish is not possible, though more improvement is needed to apply this method to large fishes.
 Next we used ABR method to measure audiograms for juvenile Japanese sand lance to determine if they are capable of sensing the sound produced by fishing vessels. And we investigated the sensitivity to ultrasound of spot-lined sardine by ABR method to know the possibility whether this fish escape when fish respond to the ultrasound that created by fisheries sonar. Japanese sand lance responded to low frequency sounds between 128 Hz and 512 Hz with sound pressure level of 115 to 125 dB. As the test frequency decreased, so did the auditory threshold level, and the level was about 116 dB at 128 Hz and 181 Hz. These results indicate that Japanese sand lance can detect low frequency sound but are less sensitive than other fish species. The ABR amplitude of spot-lined sardine to ultrasound (40 kHz, 60 kHz, 80 kHz, and 100 kHz) were approximately 0.125μV ~0.75μV. These ABR amplitudes to ultrasound stimuli were quite smaller than those of species capable of detecting ultrasound. Spot-lined sardine are not sensitive to ultrasound presentation of 40 kHz, 60 kHz,80 kHz,and 100 kHz at sound pressure levels from 180 dB to 190 dB.
 This experiment indicate that spot-lined sardine can not detect bio-sonar of porpoise and fishing echo-sounders at distance more than 100 to 300 m from sound source in spherical spreading where the sound pressure level drops less than 180 dB ~190 dB.
URI http://www.fra.affrc.go.jp/bulletin/bull/bull28/suga.pdf