Gender differences in aggression and cortisol levels in zebrafish subjected to unpredictable chronic stress

- UCS increased aggression behavior in males, but not in females.
- Females displayed more aggressive behavior at baseline than control males.
- Stressed females showed increased locomotion compared to stressed and control males.
- Stressed males had higher cortisol levels compared to all other groups.
- No differences in cortisol levels were found between stressed and control females.

Chronic stress may cause physical, behavioral and neuropsychiatric changes, affecting the health condition of an individual. Aggression is a universal behavior with great relevance on human and animal social systems. Despite studies showing the influence of chronic stress on aggression, the effects of unpredictable chronic stress (UCS) on aggressive behavior in male and female zebrafish remain unknown. Thus, the aim of this study was to evaluate the effects of UCS on the aggressive behavior and cortisol levels in adult zebrafish of both sexes. Our results showed that UCS increased aggression in males, but not in females, which displayed more aggressive behavior at baseline than control males. Increased whole-body cortisol levels were observed in stressed males; however, no differences were found between female groups. In conclusion, we reported for the first time gender differences on behavioral parameters and cortisol levels in response to UCS in zebrafish. These results highlight the relevance of studying behavioral and physiological parameters in both sexes separately.