Development and application of a new method to investigate cognition in newborn guppies

The study of cognitive abilities generally requires that each subject be assessed individually, but social isolation can be stressful, especially for newborns and young individuals. This study aimed to design learning protocols for newly born guppies based on knowledge of their social needs. In Experiment 1, in the first two weeks of life, guppies were much less gregarious than adults but spent significantly more time near social companions than near an empty compartment. When given the choice between social companions and their own mirror image (Experiment 2), they did not exhibit a preference for either virtual or real fish, indicating the possibility of using mirrors as a substitute for social companions during learning experiments. Using these data, we tested two new procedures for studying learning and memory in very young fish. Experiment 3 was a modification of the one-trial test developed for mammals in which subjects are required to discriminate between one new object and one they previously and briefly experienced. Five-day-old guppies allowed to familiarize with a tridimensional object for 20 min proved able, 30 min later, to discriminate the familiar object from a novel one differing in shape and color. For Experiments 4 and 5, we adapted a protocol for discrimination learning for adult fish: two stimuli were repeatedly introduced at opposite ends of the home tank, one reinforced with food. Using this method, we showed that nine-day-old guppies can significantly discriminate two geometric figures (a triangle from a circle) after only twelve reinforced trials.