Rotational bias in mosquitofish (Gambusia holbrooki): the role of laterality and sun-compass navigation.

Spontaneous rotational preferences in swimming of mosquitofish (Gambusia holbrooki) were investigated. Females, but not males, swam in circular tanks preferentially anticlockwise in the afternoon but not in the morning. Females' rotational preferences appeared to be related to a sun-compass orientation mechanism, as they disappeared under diffuse lighting conditions and when using naive females (i.e. using individuals never exposed to sunlight). Under repeated testing, however, the bias produced by the sun-compass mechanism tended to disappear, but females still showed rotational preferences that became stable and consistent at the individual level. Males too showed consistent individual rotational preferences under repeated testing. It is concluded that rotational bias in mosquitofish is due to two independent phenomena: a sun-compass navigation mechanism, which is related to the intensity of predation, and a behavioural lateralisation at the individual level, which is likely to reflect neural asymmetries in motor or sensory systems.