Effects of the SSRI citalopram on behaviours connected to stress and reproduction in Endler guppy, Poecilia wingei

• Guppy fish were exposed to the SSRI citalopram in the ambient water.
• No significant changes in courting behaviour were observed in males.
• Novel tank diving test revealed anxiolytic effects after 21 days exposure.
• Females showed less bottom freezing after exposure to 2.3 or 15 μg L−1.
• Males froze less and swam in the upper half of the aquarium after 15 μg L−1.

Psychoactive drugs, such as selective serotonin reuptake inhibitors (SSRI) have been identified in high levels in effluents from Swedish sewage treatment plants (STP) at concentrations high enough to give pharmacological effects in fish. In humans SSRIs are used in the treatment of depression and they have anxiolytic effects. In the present study we exposed Endler guppy (Poecilia wingei) of both sexes to citalopram that showed the highest concentrations of SSRIs in STP effluents and studied reproductive and non-reproductive behaviour. Male courting behaviours were not affected compared to control fish after 14–28 days exposure to 1 μg L−1. In two experiments exposing both sexes to 0.2, 2.3 or 15 μg L−1 for 21 days, fish exposed to the two highest doses showed anxiolytic effects when placed in a novel environment (novel tank diving test, NT). Males were only affected by exposure to 15 μg L−1. They had significantly longer latency to explore the upper half of the aquarium, more visits and longer time spent in the upper half, and showed less bottom freezing behaviour, all markers of anxiolytic behaviour. In females exposure to 2.3 or 15 μg L−1 significantly increased freezing behaviour, while no effects on other behaviour variables were observed. No effects on shoaling behaviour could be discerned. These results show that citalopram have anxiolytic effects on guppy fish and thus affect ecologically relevant behaviours of importance to survival of fish.