Fluoxetine may interfere with learning in fish.

Our study aimed to test whether fluoxetine impairs learning in fish and whether this potential impairment is reversible. Learning efficiency, with no aversive stimuli, of the Carassius carassius was analysed under different pharmaceutical conditions: (i) fish cultured without antidepressant (control), (ii) fish exposed to fluoxetine for 21 days (fluoxetine), and (iii) fish exposed to fluoxetine for 21 days and then cultured without fluoxetine for another 21 days (recovery). We exposed animals to environmental concentrations (360 ng L-1) of antidepressant. The learning rate was measured by timing how long it took the individual fish to find food and start feeding, six days in a row. The control and recovery fish took significantly less time to start eating over the six days. Control fish start eating 14 times faster than the fluoxetine fish. Fluoxetine can significantly affect learning and 21-day recovery period is not enough to fully restore the original learning abilities.

Fluoxetine results in misleading conclusions on fish behavior.

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 nontarget organisms such as fish. Fluoxetine affects fishes behavior; 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. We prepared three variants of the experiments: (a) behavioral trials with unexposed fishes, (b) behavioral trials with the same fishes after 21 days of fluoxetine exposure, and (c) behavioral trials with the same fishes after 21-day depuration period, that is, without fluoxetine. The fishes reaction time (RT), that is, difference in time spent on reaching food with and without the necessity of overcoming the obstacle, was analyzed. 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 with the nonexposed control. Share of individuals exposed to fluoxetine assigned as bold raised to 71.4% in comparison with 46.4% in nonexposed control. This sheds new light on wild fishes behavior 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.