Detecting behavioural lateralisation in Poecilia reticulata is strongly dependent on experimental design

Abstract Despite the potential benefits gained from behavioural lateralisation, defined as asymmetrical expression of cognitive functioning, this trait demonstrates widespread variation within and between populations. Numerous methodologies have been applied to investigate although whether different give consistent results has relatively understudied. In study, we assess (1) repeatability individual Poecilia reticulata ’s lateralisation indexes a classic detour assay (I-maze), quasi-circular mirror maze novel (a radially symmetric Y-maze); (2) methodological standard analysing only first ten turns in accurately quantifies lateralisation; (3) produced can be adequately explained by random chance comparing observed data unbiased ‘coin-toss’ randomisation model. We found two assays produce generally terms relative (directionality) but differed absolute laterality (intensity). The assay, however, demonstrated no similarity either assay. were reflective all undertaken during 15-min trial reducing number did exaggerate indexes. similar corresponding datasets model, with significant deviations likely individuals’ propensity perform consecutive same direction. These demonstrate need increase turning choices reduce likelihood producing spurious or exaggerated external influences. Significance statement Published studies investigating ‘handedness’, fish species used diverse array methodologies. Given variability being employed extent are lateralised which direction (left right), it is important methods From assessing three assays, was correlate measuring turn choice, strength not consistent. There correlations these an individual’s eye-use when viewing their reflection However, further investigation using model simulate replica for each brings into question patterns population differ significantly chance.