Determining the impact of caffeine on aggression in Betta splendens

Caffeine is a naturally occurring chemical stimulant found in various products that is becoming more widespread. Around 90% of the world's population consumes caffeine daily, which is absorbed and released into the body in the form of fluids. Consequently, caffeine has appeared in aquatic environments around the world as wastewater contains human fluids that contain caffeine. However, its effects and safety for the health of humans and wildlife remain inconclusive. Thus, in our study, we investigated the impact of varying caffeine concentrations on the aggressive behavior of the Siamese fighting fish Betta splendens territory holders after seeing an intruder. We compared aggression among four experimental groups, including the control group without any caffeine added, low dose caffeine (120 µg/L), medium dose caffeine (200 µg/L), and high dose caffeine (280 µg/L). We predicted that if there was an increase in the caffeine concentration, then the B. splendens would exhibit more aggressive behaviors because of the natural tendency of caffeine to stimulate movement. We found that caffeine exposure did not significantly alter male territory-holding behavior in B. splendens. A better understanding of the relationship between the biological systems of B. splendens responsible for aggressive behavior and caffeine is needed to clarify the urgency of the issue of increasing caffeine concentrations found in bodies of water worldwide.