Pharmaceuticals that end up in our aquatic environment continue to increase. In recent years, serotonin re-uptake inhibitors (SSRI) have increased in usage as it is considered safer than other substances to treat depression.  Fluoxetine (Prozac) is a widely used anti-depressant that commonly leak out after human use to aquatic environments. Although widely spread, the impact of fluoxetine on aquatic animals in is poorly investigated. The objective of this study was to see if fluoxetine impacts the behaviour of freshwater isopod Asellus aquaticus. Asellus aquaticus were exposed to an ecologically relevant concentration of fluoxetine for 28 days. Through a series of behavioural assays designed to measure the personality traits boldness, activity, exploration and escape behaviour, Asellus aquaticus responses were investigated. A. aquaticus can differ greatly in phenotype, from non-pigmentation to dark pigmentation. Further objective was therefore to investigate if pigmentation correlated with any of the measured behavioural responses, due to potential across-reaction between serotonergic and melatoneric systems. I found that fluoxetine reduced boldness, but had no effect on activity, exploration or escape behaviour. Furthermore, I observed no correlation between pigmentation and behaviour measured in fluoxetine exposed, or control animals. These results indicate that fluoxetine at low levels  affect boldness of wild A. aquaticus but no other personality traits explored. However, other research contradicts these results and show that fluoxetine can affect a range of behaviours. Taken together fluoxetine can have ecological impact on aquatic environments. Hence, our residual pharmaceuticals can have ranging effects.