Impact of Short-Term Total Dissolved Gas Supersaturation on Cognitive Functions and Swimming Performance in Medaka (Oryzias latipes)

Abstract

During the flood season, high dam operations for flood discharge result in total dissolved gas (TDG) supersaturation. This condition causes gas bubble trauma (GBT) and can even lead to fish mortality, posing a significant threat to downstream river ecosystems. Assessing the ecological risks of TDG presents a major challenge in water power-intensive river basins worldwide. Limited research has explored the impact of TDG on fish behaviors such as aggression and memory, which are crucial for feeding, reproduction, and predator avoidance. This study investigated the effects of acute TDG supersaturation stress on swimming behavior, aggression, and memory in medaka. Results indicated that Medaka exposed to 115% and 130% TDG supersaturation for 2 hours showed significantly reduced swimming performance. At TDG levels of 100%, 115%, and 130%, medaka displayed activity rates in the mirror arm of 44.34 ± 12.88%, 40.27 ± 15.44%, and 35.35 ± 16.07%, respectively, and in the active stimulus arm of 50.35 ± 14.75%, 40.76 ± 12.51%, and 35.35 ± 18.47%, respectively. As TDG levels increased, both aggression and memory in medaka significantly declined. The findings of this study could contribute to developing a TDG ecological risk assessment model based on fish memory and aggression, providing essential data for ecological management strategies to mitigate the adverse effects of TDG.