Effects of rearing in environments of different geometry on spatial reorientation in redtail splitfins fish (Xenotoca eiseni)

Following spatial disorientation in a rectangular enclosure, a variety of animal species have been proved to be capable to reorient themselves using geometric (sense and metric) or nongeometric (featural) information. Here we investigated the effect of rearing redtail splitfins fish (Xenotoca eiseni) in environments of different shapes on their ability to reorient themselves. After rearing fish singly in a rectangular or circular enclosure, they were trained in a rectangular enclosure with a wall of a different colour (so-called Blue-Wall test) and then tested at different ages (7-10 days or 30-40 days) with an affine transformation (moving the wall from a small to a large wall) that produced a conflict between geometric and nongeometric information. During training no effect of rearing was observed in animals tested at 7-10 days of age. In contrast fish reared in a rectangular environment were faster to learn when tested at 30-40 days of age. This suggests that although experience in environments with different shapes may affect spatial orientation, it is not necessary to encode geometric information in itself (in fish tested at 7-10 days of age learning was accomplished with identical velocity irrespective of the rearing conditions). At test, with the affine transformation, fish chose the geometrically correct corner far from the feature (the Blue Wall) more than its rotationally equivalent near it. The reason for this paradoxical avoidance of the feature following the affine transformation could be related to stress effects induced by rearing in social isolation, that are known to exacerbate fear responses in these animals (also revealed by reduced level of responding). Further research with socially-reared animals kept in environments of different shapes are needed to clarify this issue.