Individual differences in numerical skills are influenced by brain lateralization in guppies (Poecilia reticulata)

A large number of studies showed that fish possess numerical abilities similar to those reported in mammals and birds. However, inter-individual differences in numerical performance are repeatedly found with different types of stimuli and methodological approaches. A recent study on guppies, Poecilia reticulata, suggested that strongly lateralized individuals, assayed for eye preference in a mirror test, were better than poorly lateralized ones when tested for numerical abilities in a natural shoal choice. This study, however, had a potential confound; both the mirror and the shoal choice tests exploit the higher sociality and schooling tendencies in guppies. It is therefore possible that sociality rather than lateralization per se may have been responsible for the observed differences. In the present study, guppies were selected for high or low lateralization using a non-social test, the detour test. Subjects preferentially turning rightward (RD) or leftward (LD) when facing a dummy predator visible behind a barrier proved better than those with no preference (NL) when required to choose the larger of two groups in a shoal choice test. Our study supports the notion that inter-individual differences in the numerical abilities of guppies are related to their degree of cerebral lateralization.