Abstract
To explore behavioral responses to sound and the detectable frequency range of Octopus ocellatus, responses of the octopus to 120 dB rms sound stimuli of various frequencies were observed. The octopus did not respond at 200-1000 Hz, but clearly responded at 50-150 Hz by showing lengthened respiratory activities. Their respiratory activity was frequently suppressed for more than 5 sec after the sound stimulation, and the longest respiratory suppression reached 55.6 sec, while the mean respiratory activity length without sound stimulation was 1.23 sec. In the case of long-lasting respiratory suppression, they retracted the basal parts of their eyes simultaneously. This suggests that underwater sound may play an important role in the life of the octopus, possibly to detect predators.
