Waterborne citalopram has anxiolytic effects and increases locomotor activity in the three-spine stickleback (Gasterosteus aculeatus)

• Anxiety is affected by environmentally relevant concentrations of citalopram as demonstrated by the novel tank and novel object tests.
• Locomotor activity is increased by environmentally relevant concentrations of citalopram.

Citalopram is an antidepressant drug, which acts by inhibiting the re-uptake of serotonin from the synaptic cleft into the pre-synaptic nerve ending. It is one of the most common drugs used in treatment of depression, it is highly lipophilic and frequently found in sewage treatment plant effluents and surface waters around the world. Citalopram and other selective serotonin re-uptake inhibitors have, at concentrations that occur in nature, been shown to have behavioural as well as physiological effects on fish and other animals. This study is the result of several different experiments, intended to analyse different aspects of behavioural effects of chronic citalopram exposure in fish. Our model species the three-spine stickleback is common in the entire northern hemisphere and is considered to be a good environmental sentinel species. Female three-spine sticklebacks were exposed to 0, 1.5 and 15 μg/l nominal concentrations of citalopram for 21 days and subjected to the novel tank (NT) diving test. In the NT test, the fish exposed to 1.5 μg/l, but not the 15 μg/l fish made a significantly higher number of transitions to the upper half and stayed there for significantly longer time than the fish exposed to 0 μg/l. The 15 μg/l group, however, displayed a significantly lower number of freeze bouts and a shorter total freezing time. The test for locomotor activity included in the NT test showed that fish treated with 1.5 and 15 μg/l displayed a significantly higher swimming activity than control fish both 5–7 and 15–17 min after the start of the experiment. In the next experiment we compared fish exposed to 1.5 μg/l and 0.15 μg/l to pure water controls with regard to shoaling intensity and found no effect of treatment. In the final experiment the propensity of fish treated with 1.5 μg/l to approach an unknown object and aggressive behaviour was investigated using the Novel Object test and a mirror test, respectively. The exposed fish ventured close to the unknown object significantly more often and stayed there for significantly longer time than unexposed fish. The aggression test yielded no statistically significant effects. It is concluded that citalopram changes the behaviour of the three-spine stickleback in a way that is likely to have ecological consequences and that it must not be considered an environmentally safe pharmaceutical.