Individual Differences in Boldness Influence Working Memory and Stress-Induced Repetitive Behaviors in Zebrafish.

Individual differences in traits, such as boldness, significantly impact survival and adaptability by shaping responses to environmental challenges, including stress. Bolder individuals take greater risks to access resources and often display higher impulsivity, affecting behavioral domains like memory and cognition. Coping mechanisms in response to stressful situations may also differ between bold and shy individuals, with bold fish tending towards impulsive, less inhibited responses, whereas shy fish adopt cautious, controlled strategies. Despite these distinctions, the connections between boldness, stress reactivity, cognitive performance, and maladaptive behaviors remain poorly understood. Here, we used the zebrafish (Danio rerio) to examine these relationships. Boldness was assessed using the novel tank diving test, classifying fish as bold or shy based on overall and vertical exploratory activity. We then exposed fish to conspecific alarm substance (CAS), an acute naturalistic stressor, and assessed cognitive outcomes in the FMP Y-maze. Our results revealed distinct responses, with bold zebrafish showing poorer working memory performance and higher levels of repetitive behaviors following stress compared to shy fish, underscoring the impact of individual differences on stress reactivity and cognition. A positive correlation between boldness and repetitive behaviors was found for both control and CAS-exposed fish, indicating that boldness influences the escape strategies adopted by different phenotypes on the FMP Y-maze, especially in patterns associated with repetitive behaviors. These findings advance our understanding of how boldness influences stress responses and cognitive outcomes, providing a framework to examine resilience, impulsivity, and repetitive behaviors in translational neurobehavioral research.