Signatures of individuality in European seabass: Behaviour, cognition and telencephalic gene expression

Individual differences in behaviour and cognition are increasingly recognized as a central component of animals' cognitive processes, yet their neurobiological basis remains poorly understood in fish. Here, we investigated behavioural and cognitive individuality in juvenile European seabass (Dicentrarchus labrax) using an integrative approach combining behavioural assessment in an inhibitory control test (cylinder test) and analysis of gene expression in the telencephalon. Although successful inhibitory control responses were rare, consistent individual differences emerged in exploration, persistence and coping style throughout all experimental phases. Inter-individual variability remained stable and was organised along a continuous gradient of stress coping styles, ranging from more reactive to more proactive profiles, rather than fitting into discrete categories. At the neurobiological level, transcriptomic analyses revealed two opposing gene sets: one associated with neuronal activation and synaptic plasticity, and the other related to neuroendocrine regulation and the stress response, showing partial and non-linear correspondences with the observed behavioural profiles. Taken together, these findings support the view of individuality as an emergent and multidimensional trait in European seabass and suggest that performance in cognitive tasks should be interpreted by considering inter-individual variation in behaviour and the associated neurobiological correlates.