Stressor controllability modulates the stress response in fish.

Area of Science:

• Neuroscience
• Ethology
• Evolutionary Biology

Background:

• Psychological factors, such as predictability and control, significantly modulate the stress response in humans and mammals.
• The presence of psychological stress modulation in fish, a divergent vertebrate lineage, has remained unestablished.
• The absence of a cortex in fish has been used to argue against psychological stress in these animals, impacting welfare assessments.

Purpose of the Study:

• To investigate the occurrence of psychological stress in fish.
• To assess how stressor controllability influences the stress response in European seabass (Dicentrarchus labrax).

Main Methods:

• European seabass were exposed to controllable or uncontrollable stressors.
• The impact of losing control (transitioning from controllable to uncontrollable) was evaluated.
• Behavioral and circulating cortisol levels were measured to assess stress responses.
• Brain activity in specific homologous regions (Dld, Dlv, Vv) was analyzed.

Main Results:

• Perceived control significantly reduced the stress response compared to uncontrollable situations.
• Losing control had the most severe detrimental effect on the fish.
• Brain activity in Dld and Dlv homologues correlated with uncontrolled and loss of control stressors, respectively.

Conclusions:

• Psychological modulation of the stress response appears to be evolutionarily conserved across vertebrates.
• These mechanisms are implemented by different brain circuits in fish (Dld-Dlv) compared to mammals (prefrontal cortex).
• Findings support the existence of psychological stress in fish, with implications for their sentience and welfare.