Ontogeny of zebrafish behaviors: comparative evaluation of locomotor, social and anxiety parameters in larval, juvenile and adult stages.

Zebrafish are a prominent model for investigating behavior and development. However, most behavioral studies have primarily focused on larval and adult stages. The juvenile stage-a critical period of neural and behavioral maturation-has been insufficiently explored, partly because standardized methods for evaluating behavior in different ages are not available. Here we present a behavioral platform adapted for cross-stage assessments and provide an initial characterization of juvenile zebrafish behavior. Locomotion, anxiety, social interaction and scototaxis were evaluated. Our findings reveal developmental stage-specific differences in juvenile zebrafish locomotion, such as increased mobility and reduced erratic movements, along with a steady and progressive increase in social preference from late larval to the adult stage. Scototaxis reversal was also found to be one of the first major behavior transitions, occurring early in the larval stage. These results establish juveniles as a transitional phase with distinct phenotypes and support previous hypotheses that a behavioral metamorphosis accompanies morphological changes of juveniles in these species. Furthermore, this study establishes a foundation for longitudinal behavioral analyses, with the standardization of tests enabling further studies on neurodevelopmental disorders, pharmacological interventions and behavioral ontogeny.