<p>Sertraline is a widely used antidepressant that has been detected in aquatic environments globally and can accumulate in aquatic organisms. Sertraline affects behavior by interacting with multiple neurological pathways, including the serotonergic system. In this study, male Arabian killifish (<i>Aphaniops stoliczkanus</i>) were exposed to nominal concentrations of 0, 5, and 50 ng/L sertraline (measured values: &lt; 5and 9) for 42 days, and their behavior in a complex habitat was measured, with and without chemical predation cues. Killifish exposed to sertraline were bolder than controls in the absence of predation cues; however, they showed stronger responses to the alarm than controls. Fish exposed to sertraline were also more aggressive and engaged in more chases and fights than controls. Fish exposed to 5 ng/L sertraline displayed the highest number of chases before the addition of predator alarm cue, while significantly decreasing the number of chasing events after the addition of the alarm cue. Fish treated with 50 ng/L sertraline engaged in more fights with other males, indicating elevated levels of aggressiveness compared to control fish. The main finding of the present study is that sertraline can cause significant changes in killifish behavior at concentrations likely to be encountered in the wild. It also highlights the importance of testing behavior in a complex arena that allows the fish to display a range of natural responses.</p>