Cardiac and ventilatory arousal responses and their habituation in goldfish: effects of the intensity of the eliciting stimulus.

Recordings were made of cardiac and ventilatory responses of goldfish to the onset of 10 sec illumination presented at 2 min intervals. These responses were measured by increases in cardiac interbeat interval, ventilatory interbreath interval and by reductions in ventilatory amplitude. Four groups of fish were subjected to intensities of 52, 78, 90 and 160 lux. Habituation of responses was considered to have occurred when its magnitude fell within the limits of normal variation of the physiological variable. It was found that the more intense the stimulus the greater was the magnitude of the initial physiological response and correlated with this the number of stimulus presentations required for habituation. The relationship between stimulus intensity, initial response magnitude and resistance to habituation was consistent for cardiac responses. The results are discussed with respect to current knowledge of arousal and its habituation.