Integrating behaviour, physiology, and immune response to social stress in fish.

Dominance hierarchies in fish are established through conflicts and lead to significant differences in stress physiology, behaviour, and immune function between dominant and subordinate individuals. This review explores the relationship between social stress within these hierarchies, individual variations in stress responses and cognitive bias towards stressful situations, and the impact of conflicts on future performance and interactions between stress and the immune system. Fish express divergent stress coping styles (proactive and reactive) that differ in the reactivity of the stress axes ending with the release of the major stress hormones (adrenaline and cortisol). Social stressors, like conflicts, are perceived differently by proactive and reactive fish, leading to varying levels of stress hormone release. The stress hormones interact with the immune system, changing individuals' ability to fight off pathogens. Pro-inflammatory cytokines highly activated in reactive individuals under stress can provide feedback to the monoaminergic system in the brain, resulting in depression-like, anxiety-like, or "sickness" behaviour. The review also discusses strategies for reducing social stress in fish and enhancing their overall health in aquaculture, while emphasising the importance of considering these factors in research settings to prevent data bias.