Fig. 1

Fig. 1 (a) Schematic of the experimental setup. The animal was suspended in a mesh sling in the middle of the experimental tank (8.5 cm below water surface, and 8 cm above underwater speaker). Fresh aerated water was delivered by an elevated water reservoir with a water line that continuously provided fresh water into the fish's buccal cavity. Two electrodes were directly inserted subcutaneously into the skin on the fish's head. The positive electrode (red) was inserted between the nares on the rostral part of the head, and the negative electrode was inserted in the midline of tested fish at the opercular opening above the otic capsule (where the inner ear is located, colored in blue). The ground electrode (not shown) was placed in the tank water. (b) Acoustic characteristics (impedance and phase difference between sound pressure and particle velocity) of the experimental tank and the speaker. Top 3 panels: Acoustic impedance [ratio of sound pressure (dB re: 1 µPa) to particle velocity (dB re: 1 ms−1)] in three axes (X, Y, Z) relative to 1.504 MRayls (the reference impedance for a free-field in fresh water at 28 °C) is plotted for all tested frequencies at three representative sound pressure levels: 115, 133, 151 dB re: 1µPa. Measurements were made using a triaxial accelerometer placed in the center of the tank and water column (8 cm above the speaker and 8.5 cm below the water surface). Multiple measurements (n = 8) for both sound pressure and particle velocity were made at each frequency and sound pressure level. Data plotted are mean ± 1 standard deviation. Bottom panel: Plotted are the phase differences (ΔΦ_p,v) between the pressure and particle velocity wave. Multiple phase difference measurements (n = 8) were made at each frequency and sound pressure level. Data plotted are mean ± 1 standard deviation.