Behavioral detection of acoustic particle motion by a teleost fish (Astronotus ocellatus): sensitivity and directionality.

Behavioral detection thresholds for oscars (Astronotus ocellatus) were measured in response to linear, oscillatory motion at 100 Hz along seven axes (-90 degrees, -60 degrees, -30 degrees, 0 degree, +30 degrees, and +60 degrees in azimuth, where 0 degree is the fish longitudinal axis; and the vertical axis) using a cardiac classical conditioning paradigm. Thresholds at all selected axes ranged from -58 to -56 dB re: 1 micron, which corresponds to 1.2 to 1.6 nm displacement (RMS). Thus, oscars appear to be equally sensitive to stimulation at all axes in three dimensional space. Behavioral thresholds of the oscar are close to the neural thresholds obtained from the most sensitive auditory nerve fibers in two other species, the goldfish (Carassius auratus) and the toadfish (Opsanus tau).