SUMMARY : The role of vision in the entry of the cuttlefish Sepia esculenta into basket traps was examined in laboratory experiments and by histological examination of the retina. Both entry into the trap and feeding on shore crabs stopped when the tank was completely darkened. The eyes of cuttlefish have a high sensitivity to light. The visual field of cuttlefish was determined by the optical method, based on the assumption that incident light on the pupil from any direction reaches the retina through a refractive lens. The uniocular visual field was found to be 253° on the horizontal plane, and the anterior and posterior binocular visual fields were 86° and 60° respectively. On the retina, areas with especially high visual cell density formed a visual equator slightly above the optical equator. The distribution of the visual cell density indicates no specific visual axis. The visual acuity is 0.36 when estimated from the bait recognition distance and the size of bait during feeding, and 0.89 when determined from the visual cell density at the visual equator and the focal length of the lens. Cuttlefish have far superior visual acuity than fish.

In the present study, trapping experiments and observations on the behavior of immature cuttlefish Sepia esculenta towards the traps were made under field and laboratory conditions. Trapping experi ments clearly demonstrated the entry of immature cuttlefish into the basket traps. The entry rate was sig nificantly higher in immature than in mature cuttlefish studied in the same laboratory conditions. When entering and leaving the trap, cuttlefish swam straight primarily with arms in front, thus suggesting their active movement.After entry, cuttlefish remained stationary at the bottom. Females stayed in the trap longer than 3 days, while males left within 3 days. The existence or the position of branches did not influence the entry of cuttlefish into the traps. These results may rule out the possibility that spawning is a motivation for the entry of cuttlefish into the traps.