Chilled-out trout (Image: Gerard Lacz/NHPA)

IF TROUT in the St Lawrence seaway around Montreal, Canada, look less stressed than usual, it could be that they’re chilling out on Prozac.

For three months, Sébastien Sauvé at the University of Montreal exposed groups of 50 native brook trout to sewage from the city’s sewage works, mixed with clean water from the St Lawrence (Chemosphere, DOI: 10.1016/j.chemosphere. 2010.12.026).

After screening their liver, brain and muscle, they found several well-known antidepressants, including fluoxetine, better known as Prozac, and paroxetine, aka Paxil or Seroxat. Although the amounts were small – typically less than a nanogram of drug per gram of fish tissue – Sauvé warns that over time, the drugs could impact their behaviour and ecology. He and his team showed that the brain cells of fish exposed to the effluent in a Petri dish were less active than normal cells.


Sauvé has not yet monitored the fish for changes in courtship or other behaviours, but says the study raises enough questions to dig further.

He adds that levels of the drugs in the fish muscle were so tiny they would pose no risk to consumers.

The bigger worry is whether fish health and ecology is being affected by effluent from a city where some 500 million antidepressant pills are purchased each year – a level Sauvé says is likely to be comparable with other big cities.