Distance estimation in the Goldfish (Carassius auratus)

Neurophysiological advances have given us exciting insights into the
systems responsible for spatial mapping in mammals. However, we are still
lacking information on the evolution of these systems and whether the
underlying mechanisms identified are universal across phyla, or specific
to the species studied. Here we address these questions by exploring
whether a species that is evolutionarily distant from mammals can perform
a task central to mammalian spatial mapping – distance estimation. We
developed a behavioural paradigm allowing us to test whether goldfish
(Carassius auratus) can estimate distance and explored the behavioural
mechanisms that underpin this ability. Fish were trained to swim a set
distance within a narrow tank covered with striped pattern. After changing
the background pattern, we found that goldfish use the spatial frequency
of their visual environment to estimate distance; doubling the spatial
frequency of the background pattern resulted in a large overestimation of
the swimming distance. These results provide robust evidence that goldfish
can accurately estimate distance, and show that they use local optic flow
to do so. These results provide a compelling basis to utilise goldfish as
a model system to interrogate the evolution of the mechanisms that
underpin spatial cognition, from brain to behaviour.