Investigating the interplay of social defeat stress and personality in male and female zebrafish

<p dir="ltr">Psychological stress is now a known cause for many aspects of health deterioration or worsening of already existing health conditions. The way individuals interact with their environment and potential stressors depends on many factors including their personality background, upbringing, social experience, sex or age. This can translate into different coping strategies and different health consequences. In this thesis, the response to a stressful social experience and the effects of the resulting chronic stress are investigated using zebrafish (Danio rerio) as a model. A protocol of social defeat stress induced through dyadic fights was applied, and to better understand the interaction between social experience and personality, two lines of zebrafish were used, characterized by different coping styles, reactive and proactive (and hence different personality trait phenotypes, namely shy and bold). Sex differences were also considered, and the experiments were executed with both male and female individuals. A variety of parameters were measured to assess the consequences of social defeat stress and the overall health status of the animal: body condition, behavioral response (mirror test, zMCSF), and gene expression in the brain, intestine and skin (RNA sequencing). In summary, we showed that in both males and females inherited coping styles (personality) had a stronger effect on the response to social stress at various levels than the acquired social rank. Nevertheless, the lower social rank of subordinate/loser fish enhanced those effects, and those individuals appeared more vulnerable to subsequent health impairments, notably with signs of higher inflammation in the gut or signs of potential injuries and wound healing in the skin. Together, the data highlights the complexity of the response to stressors and the benefits of including unusual but very influential factors such as inherited personality traits in the experimental design. The data also supports previous findings showing that chronic stress can lead to potential impairment of health.</p><h3>List of scientific papers</h3><p dir="ltr">I. Hubená, P., <b>Benrejdal, L.</b>, Brodin, D., Axling, J., Sarma, O.S., Bergman, P., Winberg, S</p><p dir="ltr">Effects of Stress Coping Styles and Social Defeat on Zebrafish Behaviour and Brain Transcriptomics<br>Neuroscience Bulletin, Sep. 2025<br><a href="https://doi.org/10.1007/s12264-025-01506-0" rel="noreferrer" target="_blank">https://doi.org/10.1007/s12264-025-01506-0</a><br><br></p><p dir="ltr">II. <b>Benrejdal, L.</b>, Hubená, P., Brodin, D., Morales Castro, R.A., Rekha, R.S., Winberg, S., Bergman, P.</p><p dir="ltr">Personality and repeated social defeat affect health condition and gene expression in the skin and intestines in zebrafish<br>Progress in Neuro-Psychopharmacology and Biological Psychiatry, Sep. 2025, p. 111487<br><a href="https://doi.org/10.1016/j.pnpbp.2025.111487">https://doi.org/10.1016/j.pnpbp.2025.111487</a><br><br></p><p dir="ltr">III. Hubená, P .* , <b>Benrejdal, L</b> .* , Brodin, D., Morales Castro, R.A., Bergman, P., Winberg, S.</p><p dir="ltr">Coping with Stress: Behavioural and Transcriptomic Profiles Across Tissues in Female Zebrafish <br>[Manuscript]<br></p><p dir="ltr">*Equal contribution</p>