Shyness and behavioural asymmetries in larval zebrafish (Brachydanio rerio) developed in light and dark

This is the first study analysing individual differences in shyness–boldness and behavioural asymmetries in young zebrafish larvae (fry, 7 days post-fertilisation). Individual differences were more stable in tests with predator model (crude image of a fish face) than with an arbitrary novel stimulus (vertical black stripe). Principal component analysis revealed a dimension of ‘shyness’ that involved the tendency of fry to avoid a predator model and reduced locomotion in its presence. The fry took longer to enter a novel environment and kept at greater distance when the stimulus was first seen with the left rather than right eye. Individual differences in eye use were consistent with either novel stimulus or predator model, but there was no correlation between these two contexts. Shyness correlated with left eye bias for viewing novel stimulus but not predator model. Development of eggs and larvae in darkness during the first six days after fertilisation increased shyness and reduced behavioural asymmetries in response to the predator model.