Time-place learning in golden shiners (Pisces: Cyprinidae)

The goal of this study was to determine whether fish can learn to forage in different places at different times of the day, each place being associated with a specific time. Groups of eight golden shiners (Notemigonus crysoleucas) were kept in aquaria equipped with automatic feeders that dropped food on one side in the morning and on the other side in the afternoon, or on one side in the morning, the other side at midday, and back on the first side in the evening. After 3-4 weeks, food was withheld and the position of the fish within the aquaria was noted at 5-min intervals throughout the day. Consistent with time-place learning, most fish were on the correct side at the correct time. However, another experiment with three places instead of two provided only equivocal evidence of time-place learning; this could reflect the fact that, in the lakes they inhabit, golden shiners may need only distinguish between two places: open waters and littoral. Experiments with phase-shifts of the photoperiod showed that temporal discrimination is based on a circadian clock that can be gradually phase-advanced by 6 h in about 3 days.