Ontogeny of learning and visual discrimination in zebrafish

Summary With the exception of humans, early cognitive development has been thoroughly investigated only in precocial species, well developed at birth and with a broad behavioural and cognitive repertoire. We investigated another highly altricial species, the zebrafish, Danio rerio , whose embryonic development is very rapid: 72 hours. The nervous system of hatchlings is poorly developed, and their cognitive capacities are largely unknown. Larvae trained at 8 days post-fertilisation rapidly learned to associate a visual pattern with a food reward, showing significant performance at 10 days post-fertilisation. We exploited this capacity to study hatchlings’ discrimination learning capacities. Larval zebrafish rapidly and accurately learned colour and shape discriminations. They also discriminated a figure from its mirror image and from its 90°-rotated version, although with lower performance. Our study revealed impressive similarities in learning and visual discrimination capacities between newborn and adult zebrafish despite their enormous differences in brain size and degree of development.