Observational learning improves predator avoidance in hatchery-reared Japanese flounder Paralichthys olivaceus juveniles

The level of importance of learning in the survival of an animal is related to its evolutionary status, environmental demands, and developmental stage. This paper examines the role of learning in predator avoidance of Japanese flounder Paralichthys olivaceus juveniles. We conditioned flounder juveniles to predation using two different methods: (1) direct exposure to a predator, and (2) allowing juveniles to observe predatory attacks on conspecifics. Predator avoidance performance and feeding behaviour were then compared among predator-exposed, predator-observed and naïve individuals. Both predator-exposed and predator-observed fish were better at avoiding a predator than were naïve fish when they encountered a predator 6 h after the initial exposure. Although this effect was not significant 24 or 30 h after exposure, reaction distance to a predator was longest in predator-exposed and shortest in naïve fish 6, 24 and 30 h after exposure. When fed pellets, predator-exposed and predator-observed fish showed less off-bottom feeding behaviour and their heights of swimming were lower than those of naïve fish. We conclude that flounder juveniles are capable of predator conditioning both through direct and observational learning processes.