We hypothesize that O. vulgaris will switch their activity time in response to the visual and chemical presence of two different species of fish that are potentially predators or competitors of octopuses, the moray eel Muraena helena ( Hanlon and Messenger, 1996) and the triggerfish Balistes carolinensis ( Tortonese, 1986). The two fish predators vary in their activity cycle as well as in their style of hunting and foraging. On the one hand, the nocturnal moray eels are specialized in a benthic life style; they move on the substrate and venture into crevices and under rocks, enabling them to forage for and hunt octopuses outside and inside their dens.