Behavioural lateralisation of the tetrapod type in the zebrafish (Brachydanio rerio).

Visual lateralisation resembling that found in a bird (domestic chick) is here demonstrated in a teleost (zebrafish, Brachydanio rerio). Zebrafish predominantly view objects with the body axis close to facing the object (0-20 degrees on either side of facing). Strange objects were viewed at first exposure chiefly with the right frontal field; so was a complex and unfamiliar scene made up of familiar components. In a second trial, using the same stimulus or scene, left frontal viewing tended to be used instead. A familiar partner (a fish of another species) was viewed left frontally. The domestic chick also uses the left eye to view familiar stimuli, shifting to the right when it has to decide what response is appropriate to the object at which it is looking. An empty scene in which nothing could be concealed (and so no response was called for) was viewed by zebrafish with the left eye from the start. In zebrafish and the chick, the right eye is used when it is necessary to inhibit premature response, in order to sustain viewing until a decision is reached, and the left is used when it is necessary to keep an eye on a familiar or clearly empty scene. The findings suggest homology of cerebral lateralisation in teleost fish and tetrapods.