How social behaviour in juvenile Brown trout (Salmo trutta) are regulated by social hierarchies and exposure to the benzodiazepine oxazepam

Sammanfattning: Improved global healthcare rises the production and consumption of human pharmaceuticals. Insufficient wastewater treatment systems and unregulated downstream impacts causes pharmaceutical contamination of surface waters with trace residues in countries covering all continents. Earlier studies of aquatic systems have shown that pharmaceutical exposure influences fish physiology and causes behavioural responses at both individual and ecosystem level. Here, I evaluated how social status in juvenile brown trout (Salmo trutta) influenced behaviour after exposure to an anxiolytic drug (the benzodiazepine, oxazepam). For this project, the fish were exposed to one of three oxazepam treatments: one low, environmentally relevant dose, one high, human therapeutic relevant dose, and one control dose without oxazepam. I expected decreased aggressive behaviour and mitigated relations between dominant and subordinate individuals. Contrary to the prediction and to earlier documentation of fish behavioural responses to oxazepam exposure, neither of the treatments in this project resulted in altered social hierarchies. Moreover, there were no significant differences in brown trout aggression between the treatment groups. The interspecies variations and the relatively unexplored effects of pharmaceutical exposure on social behaviour motivates further studies, preferability over longer time periods with environmentally realistic contexts. This information should be used to improve pharmaceutical regulations and legislation for ecological risk assessments.