O. vulgaris were collected by fishing pots in the Bay of Naples (Italy),
immediately transported to the laboratory, weighed (range: 98–1268 g;
mean ±SEM: 533.39 ± 88.90) and sexed. Only individuals in apparently
good conditions and without any injury were used for the subsequent
experiments. Newly caught wild octopuses were left alone in a darkened
tank supplied with continuously running sea water and fed with crabs
(Carcinus mediterraneus) for some days. Before the experiment all
octopuses were moved in contiguous experimental PVC tanks (150 l),
covered with a translucent PVC lid to limit animals from escaping. Dark
sand was used as substratum and two bricks were placed in a corner to
serve as a den. Tanks were supplied with continuously running sea