Exposure to Environmental Levels of Fluoxetine and Atrazine Increases Latency to Aggression in the Siamese Fighting Fish, Betta splendens

This study investigates the effects of environmentally relevant concentrations of atrazine and fluoxetine, both individually and in combination, on aggressive behavior in male Betta splendens (B. splendens). Controlled behavioral assays were used to test the hypothesis that both individual and combined exposures would alter aggressive behavior, primarily by delaying the initiation of aggression and reducing the duration of specific displays. Twelve low-concentration (15 µg/L atrazine; 0.54 µg/L fluoxetine) and six high-concentration (30 µg/L atrazine; 1.08 µg/L fluoxetine) acute exposure trials were conducted. Latency to respond (LTR), broadside display (BSD), and frontal display (FD) were recorded over three days of male conspecific interactions. We analyzed the results using a negative binomial general linear model with day, atrazine, fluoxetine, and the interaction between the two compounds as predictors of the three behavioral responses. Results found that exposure to both compounds at either concentration significantly reduced aggressive behaviors compared to controls, increasing the latency to respond and decreasing broadside display and frontal display. For the low-concentration experiments, there were significant antagonistic effects from the interaction between fluoxetine and atrazine for all three behavioral responses (LTR p = 0.002, BSD p < 0.001, FD p < 0.001), with the combination of the two compounds showing a smaller impact than predicted by each singly. For the high-concentration experiments, there was a significant antagonistic interaction for BSD (p < 0.0001) and a marginally significant antagonistic interaction for LTR (p = 0.078). These findings suggest that these compounds can delay the onset and reduce the intensity of aggressive behaviors, underscoring the potential disruption of neurobehavioral pathways essential for survival, though the impact of these chemicals is altered by exposure conditions. This research highlights how environmental concentrations of common contaminants, especially in combination, may impair ecologically relevant behaviors in chemically impacted freshwater habitats.