Mosquitofish (G. holbrooki) exposed to fluoxetine (FLX) at two realistic levels. FLX at the lower level increased activity in the presence or absence of a predator. FLX at both levels reduced latency to enter predator strike zone. FLX caused sex-dependent reduction in ‘freezing’ after a simulated predator strike. Exposure to FLX can have detrimental sub-lethal impacts on antipredator behaviour.