Abstract:
The acoustic startle reflex in goldfish (Carassius auratus) was studied experimentally in the large acoustic tank at Georgia Tech. Individual free swimming fish were placed in an acoustically transparent cage and positioned in the center of the tank. Their behavior was graded for a response to acoustic signals and the direction of response with respect to the sound source. A preliminary study indicated two interesting features. First, the fish was much more likely to respond in the ``correct'' direction (away from the source) when responding to subthreshold stimuli. Second, there was strong dependence of signal amplitude at threshold on fish size. For the two weight groups tested (1.6 g, n=3 and 23.6 g, n=4), the sound-pressure level at threshold was 15 dB lower for the smaller subjects. The initial study has recently been augmented with tests on a range of subjects weighing between these two extremes. Also, since only the first half-cycle of the acoustic stimulus is thought necessary to elicit the response, the concept of frequency to characterize the sound stimulus is inappropriate. Therefore, thresholds were measured as a function of signal rise time. A parallel effort has involved modeling a biologically relevant stimulus: the acoustic field generated by an attacking predator. [Work supported by ONR.]