Too young to be bold: Lack of personality in juvenile goby

Abstract Animal personality, defined as consistent individual differences in behaviour across time and contexts, can significantly influence fitness and survival. However, the expression and stability of personality traits across ontogeny remain poorly understood, particularly in species undergoing complex life history transitions. Here, we examined behavioural consistency in juvenile two-spotted goby ( Pomatoschistus flavescens ) during the critical shift from a pelagic to a benthic lifestyle. Using two standardised assays—the emergence test (boldness) and open field test (exploration)—we assessed behavioural repeatability across repeated trials in a laboratory setting. Across most behavioural measures, we found low repeatability, with within-individual variance exceeding among-individual variance. Correlation analyses revealed consistent behavioural responses within contexts (e.g., among boldness measures), but no significant cross-context correlations, indicating that boldness and exploration do not form a behavioural syndrome in juveniles. These results contrast with findings in adult gobies and suggest that stable personality traits may not be present at this developmental stage. We propose that the observed behavioural flexibility may be adaptive, allowing juveniles to respond rapidly to the variable environmental and social conditions encountered during post-settlement. This ontogenetic plasticity may confer survival advantages in dynamic reef environments. Our findings underscore the importance of incorporating life stage and developmental context when investigating animal personality and behavioural organisation.