Fluoxetine is an antidepressant medicine causing relaxation and mood improvement in people, with silencing certain personality traits in some cases. The question arise if such phenomena can be observed in non-target organisms like fish. Fluoxetine affects fishes behaviour, however, it is not known if the medicine affects its “personality”. This study aimed to evaluate the reaction of the invasive Neogobius fluviatilis and native Gobio gobio individuals to fluoxetine at environmental concentration of 360 ng L^-1. We prepared three variants of the experiments: (i) behavioural trials with unexposed fishes; (ii) behavioural trials with the same fishes after 21-day of fluoxetine exposure; (iii) behavioural trials with the same fishes after 21-day depuration period i.e. without fluoxetine. The fishes reaction time (RT) i.e. difference in time spent on reaching food with and without the necessity of overcoming the obstacle was analysed. Additionally, the personality: bold or shy, traits of each fish individual, was assigned. The results indicated that environmental concentrations of the antidepressant influenced RT. The average RT of the fishes cultured with fluoxetine was by 7 min shorter in comparison to the non- exposed control. Share of individuals exposed to fluoxetine assigned as bold raised to 71.4% in comparison to 46.4% in non-exposed control. This sheds new light on wild fishes behaviour caught from freshwater. Environmental concentrations of the antidepressant influenced the time of fishes reaction and share individuals assigned as bold. Moreover, 21 day recovery lasting might be not enough to get fluoxetine effect on fishes.