Oral L-Dopa Disrupts Behavioral Self-Control in Male Fighting Fish (<em>Betta splendens</em>)

In their natural habitat, male Betta splendens are territorial resource defenders, whereas females are non-territorial opportunistic foragers. This ecological difference suggests that males may be more capable of delaying gratification for food rewards. The present study examined impulsive choice in Betta splendens through two experiments comparing preferences for a Smaller-Sooner (SS) reward (1 pellet immediately) versus a Larger-Later (LL) reward (3 pellets after 15 s). In Experiment I, males were significantly more likely to develop a stable preference for the LL option, whereas females were equally likely to choose either reward. These findings indicate that most males demonstrated spontaneous behavioral self-control without specialized training, while females were collectively indifferent. Experiment II investigated whether dopamine modulates this behavior by administering oral L-Dopa (60 mg/kg) to males before trials. Using the same procedures, only 30% of L-Dopa-treated males stabilized on the LL reward, compared to 70% choosing the SS option; control males were equally likely to stabilize on either reward. These results suggest that elevated dopaminergic activity increases impulsive choice in males. Future studies should examine dopamine agonists and antagonists, as well as female responses, to further clarify dopamine’s role in reward valuation and self-control in Betta splendens.