The octopuses showed temporal spacing of activity in the presence of the triggerfish. The general activity per hour of the octopuses and the general activity per hour of the triggerfish had a highly significant negative correlation between day one and day seven (Spearman rs = − 0.326, P < 0.0001). The main switching of activity occured between day four and five. The negative correlation stayed rather constant and highly significant from day one to day four and started to increase steadily by day five. By day seven the correlation reached a significant level (Spearman rs = − 0.670, P = 0.009; Fig. 3). Although the triggerfish showed more locomotor activity during the day than at night, this activity could not be characterized as exclusively diurnal. There was a highly significant effect of illumination regime on the triggerfish's locomotor activity (paired t-test, t = 4.947, P < 0.0001, N = 12).