Time–Place Learning Based on Food but not on Predation Risk in a Fish, the Inanga (Galaxias maculatus)


S. Reebs, Département de Biologie, Université de Moncton, Moncton, New Brunswick, Canada E1A 3E9. E-mail: reebss@umoncton.ca


Time–place learning, or the ability to learn to be in different places at different times of day, is already known to occur in response to daily spatio-temporal patterns of food availability. However, the ability to learn daily patterns of predation risk and move between areas at the right time of day in order to avoid predation has never been tested. This study asked whether inangas, Galaxias maculatus, are capable of time–place learning based on food availability only, predation risk only, or the antagonistic combination of food availability and predation risk. Shoals of five inangas were kept in aquaria partially divided into a right and left section. Every day they were exposed to a stimulus on one side in the morning and on the other side in the afternoon. Depending on the experiment, the stimulus could be two deliveries of food, two simulated heron strikes, or both of the above within the same hour. After 14 d the stimuli were not given and the position of the fish was noted in both the morning and the afternoon. The majority of the fish learned to switch sides at the correct daily time in order to get food, but they remained on the same side at both daily times in response to either predation risk alone or the combination of predation risk and food. It seems that the potential for time–place learning based on predation risk is less than that based on food, and that predation risk can even curtail the expression of time–place learning based on food. Fish may resort to other tactics, such as shoaling and reduced movement, in response to predation risk. Daily habitat shifts could still be present in nature and rooted in the avoidance of predation, but instead of being the direct result of learning they would be mostly innate.