Cuttlefish use the negation of dead prey to judge food value in foraging decision.

Understanding how targeted prey conditions influence foraging decisions is a fundamental issue in animal behaviour. The present study investigated whether cuttlefish use prey liveness to assess overall food quality. Cuttlefish were allowed to choose between different levels of prey freshness and quantity. Experiments 1 and 2 examined cuttlefish choices between one live shrimp alone and one live shrimp paired with either one or four freshly dead shrimps. Experiment 3 evaluated their preferences of one live shrimp paired with either one freshly dead shrimp or one hourly dead shrimp. Experiment 4 assessed their choices between these two types of dead shrimp alone. Results showed that cuttlefish significantly avoided the side containing one live shrimp paired with one freshly dead shrimp, and this avoidance increased proportionally with the quantity of dead shrimp. However, cuttlefish choice did not differ significantly between freshly and hourly dead shrimps. These findings suggest that the presence of dead shrimp decreases a cuttlefish's perceived food value, and that motionless prey, regardless of their condition, serve as a negative indicator of overall food quality. This study demonstrates that cuttlefish assess total prey value based on the negation of dead prey, a mental process of intentionally removing hindrances during evaluation.