Spatial reorientation using geometric and featural properties of an environment by fish (Xenotoca eiseni)

Recent research has shown that when disoriented in a novel environment, rats and young children reoriented themselves according to the large-scale shape of the environment, but not according to non-geometric properties of the environment such as the colour of a wall or the patterning of a distinct featural panel placed in a corner. In contrast to young children and mature rats, human adults conjoined geometric and non-geometric information. It has been claimed that their performance suggests that some representational systems become more accessible and flexible over development and evolution. However, other species (e.g. domestig fowl, pigeons, certain monkeys) also conjoined geometric and non-geometric information. We tested fish (Xenotoca eiseni) in a rectangular environment constructed to eliminate external orientation cues. Gates to escape from the arena were located in some corners that fish had to find out. When tested in an all-white tank, fish proved able to reorient themselves using purely geometric information: according to the shape of the arena, they searched the correct and the rotationally equivalent corners equally often. On the other hand, when tested in a tank with one blue wall, fish searched only the correct corner thus demonstrating that they also encoded non-geometric information. Possible reasons for species differences in the integration of geometric and non-geometric information are discussed.