The vibrational response of single-chambered fish swimbladders to low-frequency sound

The gas-filled swimbladder of a fish resonates in the ambient noise field, scattering significant amounts of acoustic energy. The Non-invasive Vibration Amplitude Measurement System (NIVAMS) was used to measure the frequency response of the swimbladder of a freshwater species, the oscar (Astronotus ocellatus Cuvier), in a range from 200 to 2000 Hz. NIVAMS uses continuous wave ultrasound to measure swimbladder vibrational displacement amplitudes in vivo. Advantages of the NIVAMS are that it is non-invasive (no surgery is required to make the measurements) and that it is non-intrusive (the motion is unaltered by the measurement process). The response of the oscar's single-chambered swimbladder followed the general characteristics of the simple theoretical model by Andreeva (1964). (C) 1996 International Council for the Exploration of the Sea