Sex-specific behavior in juvenile brown trout (Salmo trutta). Investigating the impact of sex on dominance and aggression among juvenile brown trout by using new DNA-based sex identification.

Abstract

In salmonid populations, social structures generate dominant individuals that typically display higher ag-gression, securing high-quality resources and optimize chances of survival. Studies within the subject of dominance and sex-specific behavior within adult salmonid groups concludes that salmonid males usually take on the dominant role, likely due to distinct reproductive roles between the sexes. Similar previous research on juvenile salmonids is limited and instead indicates that males are also more aggressive, but not consistently more dominant. This study addresses this gap in knowledge by combining a short-term domi-nance assessment using an artificial stream and 96 brown trout captured by electric fishing around Lunz am see, Austria, with a non-lethal DNA sex identification method using DNA from the same individuals. The study explores how residency during 10-day rounds and time of day influences the overall aggression level and when dominance is established. Additionally, it investigates how sex and group body size influences dominance and aggression. The result indicates that both residency and time of day were significantly af-fecting the overall aggression, with higher levels at dawn, consistent with earlier studies. The interaction of day and time also significantly affected the establishment of dominance, with early dominance also visible at dawn, and were overall stable from day 8. Both sexes became dominant within the groups, but the ag-gression in groups with female dominant individuals significantly increased with group body size, opposite to earlier studies. These findings may provide insight into how various factors can influence aggression and dominance in juvenile brown trout populations, which could help develop strategies for their conservation.