Behavioral effects of fluoxetine on aggression and associative learning in Siamese fighting fish (Betta splendens)

• We examined the impact of the SSRI fluoxetine on learning in a novel Go-No Go discrimination task for aggressive rewards.
• Responding on the task was impacted by exposures to a 10 μmol concentration of fluoxetine such that all aggressive behavior and task performance ceased.
• In light of past research, the present results indicate that fluoxetine may alter behavior through motor sedation or by altering the saliency of rewards.
• Serotonin likely exerts a modulatory role in reinforcement and motivational aspects of associative learning through action on dopaminergic pathways.

Past research has implicated serotonin as an important neurotransmitter in the facilitation of aggressive behavior. In Siamese fighting fish (Betta splendens), the SSRI fluoxetine has been demonstrated to reduce both frequency and duration of aggressive displays across a variety of concentration exposure procedures. While this multi-method approach has provided strong evidence for fluoxetine's impact on aggression, no study has sought to examine the behavioral mechanism by which fluoxetine exerts its anti-aggressive effect. To address this question, a Go-No Go discrimination task utilizing mirror presentations as a reinforcer was designed. Consistent with previous reports, the results indicated that fluoxetine may exert a sedative effect upon aggressive behavior via decreased arousal to external stimuli.