Fins of Fury or Fainéant: Fluoxetine impacts the aggressive behavior of fighting fish (Betta splendens)

While an extensive literature has demonstrated that the selective serotonin reuptake inhibitor (SSRI) antidepressant fluoxetine, disrupts aggressive behavior in male Betta splendens the behavioral mechanisms underlying this disruption remain unknown. To elucidate the behavioral mechanism underlying fluoxetine, male fish were acutely exposed to a 10 μmol (0.0034578 μg/L) concentration of fluoxetine for 25 days using an ABA design. Male Betta splendens are naturally aggressive fish with well-studied and patterned behavioral responses. Importantly, aggressive behavior in this species can be conditionally primed allowing for examination of motivational components of behavior in addition to motor performance. The present study focused on using female fish as an ecologically relevant prime for eliciting aggressive behavior as a means of examining the motivational and motoric effects of fluoxetine. We found that male courtship with a female was strongly correlated with aggressive responding against a mirror. However, despite the strong correlation male fish were not found to have different levels of aggression or changes in aggressive responding when compared to males not primed with a female. Also, latency was not different between the no female prime and female prime males for either the excitatory mirror condition or inhibitory white wall condition, of which the fish had no preference. However, fluoxetine was found to have profound effects on all males in the study regardless of prime type, with increases in latency for the mirror and white wall and decreases in aggressive responding to the mirror. These results support the hypothesis that fluoxetine impairs aggressive motivation and movement in Betta splendens.