Environmental enrichment affects the ontogeny of learning, memory, and depth perception of the pharaoh cuttlefish Sepia pharaonis

We investigated the effects of environmental enrichment on the cognitive abilities of pharaoh cuttlefish, Sepia pharaonis, which were reared from day seven in four different environments: isolated, poor, standard, and enriched. First, we used “prawn-in-the-tube” to test whether environmental enrichment affects the ontogeny of learning and memory of S. pharaonis. The results showed that cuttlefish could usually learn the task regardless of their age and environment. At early age (74 - 81 d), cuttlefish from the isolated environment memorized the task for 24 h. However, at later age (104 - 171 d), the isolated cuttlefish were unable to remember the task. In addition, cuttlefish from the poor environment could not memorize the task at all ages examined. Cuttlefish from the standard environment could memorize the task in later ages (134 - 171 d). In contrast, cuttlefish from the enriched environment could memorize the task at all ages examined. Second, we examined the effect of environmental enrichment on the ontogeny of depth perception of S. pharaonis by observing their hunting behavior. Distance from the prey during hunting was always greater in isolated cuttlefish than those from the other three environments. In addition, hunting success and number of prey captured were always lowest in the isolated cuttlefish for all ages. In contrast, hunting success was always the highest in cuttlefish from the enriched environment. These variations in behavior among cuttlefish raised in different environments suggest that the visual/tactic input derived from social and physical factors of the surrounding environment could promote maturation of learning, memory, and depth perception in S. pharaonis.