<p>Understanding individual variability in stress physiology is critical for improving fish welfare and optimizing production in aquaculture. This study investigates the variability of cortisol responses to acute stress in juvenile greater amberjack (<i>Seriola dumerili</i>), a species of increasing interest in Mediterranean aquaculture. It also examines whether early-life thermal exposure and individual behavioral coping styles, particularly risk-taking behavior, are associated with divergent cortisol responsiveness. Juvenile amberjacks were reared under controlled conditions and assessed for risk-taking behavior using a standardized group-based behavioral test. Acute stress responses were evaluated by measuring physiological stress indicators over time, focusing on cortisol dynamics to assess both inter-individual variability and intra-individual consistency. Results demonstrate that cortisol responsiveness is a repeatable and stable individual trait in this species, showing no significant association with early thermal conditions or behavioral profiles. While early-life temperature influenced risk-taking behavior in one experimental trial, this trait did not correlate with variability in growth or physiological stress markers. Overall, this study shows that cortisol responsiveness in juvenile greater amberjack is a repeatable individual trait, not being affected by the examined early-life temperature exposure and intrinsic risk-taking behavior, highlighting the significance of individual variability for understanding stress physiology in aquaculture.</p>