Examples of AEP traces from walking catfish stimulated with pulses of 120 dB of various frequencies of sounds (re 1 μPa). Signals were captured 2.5 to 22.5 ms after sound stimulation. Scale bars on the left indicate signal amplitudes (0.8 μV at frequencies 2.5 kHz and higher; 0.2 μV at frequencies 3.0 kHz and lower). Black lines show the standard AEP waveforms of a normal walking catfish at different frequencies. Red and blue lines show the waveforms after gas removal from the suprabranchial chamber (SC) or bladder (WGB), respectively. Green lines show the waveforms of fish in which both structures were deflated.