Learning-related performance of European seabass (Dicentrarchus labrax) and expression of c-fos and egr-1 immediate-early genes in the brain

• 10–16% of European seabass successfully learned a spatial task with positive reinforcement • Learners upregulated c-fos and egr-1 in telencephalon and hypothalamic inferior lobe • Three-day learning protocol captured IEG expression changes more reliably than eight-day • Immediate early genes validated as biomarkers of cognitive engagement in European seabass • Individual learning variability highlights need for tailored welfare training protocols Fish learning abilities play a key role in optimizing husbandry and feeding strategies. This study examines spatial learning and associated neuronal gene expression in European seabass ( Dicentrarchus labrax ), a species widely farmed in the Mediterranean. Individuals were classified as learners (L), non-learners (NL), or non-attempters (NA) based on performance in a spatial task over 3- and 8-day learning periods. Approximately 10–16% of fish successfully learned the task, showing improved trial times and increased expression of immediate early genes (IEGs) egr-1 and c-fos in the telencephalon and inferior lobe of the hypothalamus, regions linked to learning, memory, and reward processing. UL fish displayed partial neural activation but inconsistent behavioral success, likely influenced by motivation or stress, while NL fish showed behavioral apathy and lower gene expression. Prolonged training led to habituation and neural desensitization, whereas the shorter, 3-day learning better captured learning-related gene expression changes. These findings indicate that IEG expression is a reliable marker of learning-related brain activity but may also reflect stress responses. Thus, recognizing individual variability in cognitive performance and well-managed learning protocols can improve fish welfare and feeding efficiency in aquaculture.