The environmental geometry as a fish feels it.

Disoriented human beings and animals are able to use spatial geometric information (metric and sense properties) to guide their reorientation behavior in a geometrically shaped environment (e.g., rectangular). Reorientation spatial skills of three fish species (Danio rerio, Xenotoca eiseni, Carassius auratus) were investigated, in order to discover the possible involvement of extra-visual senses during geometric navigation, such as the lateral line (LL), made up of mechano-sensors (neuromasts) for hydrodynamic stimuli detection. The fish's behavior was observed in a rectangular non-visible environment, under different experimental procedures (spontaneous social cued task and rewarded exit task), providing them different temporal opportunities to experience the environmental shape (no experience, short and prolonged experience). Results showed that, by using spontaneous tasks, fishes were not able to take advantage of extra-visual senses to encode the spatial geometry but they did, by using rewarded tasks, under prolonged extra-visual experience. Therefore, in order to investigate the involvement of the LL, the reorientation behavior of zebrafish (D. rerio) was observed, after inducing a pharmacological ablation of the LL, by administering gentamicin. A mitochondrial staining procedure with the DASPEI fluorescent vital dye was performed to visualize the LL neuromasts of controls vs. gentamicin-treated fish. Despite the treatment, zebrafish reoriented correctly, leading to the exclusion of LL as a pivotal way to solve the geometric reorientation. On the other hand, movement strategies mainly highlighted a perimeter exploration, closely adhering to the surfaces, thus emphasizing the role of touch and its multimodal integration in constructing an internal representation of the environmental geometry.