Higher temperatures distinctly affect the brain mitochondrial respiration of two Amazonian fishes, a predator and a...

The aquatic biota of the Amazon is subject to considerable daily and seasonal fluctuations in its environment. The ability to adapt to changes in the environment, such as increased water temperatures, is essential for the survival and physiological performance of these organisms. The anticipated rise in temperature and CO₂ levels, projected to reach 6 °C and 50% above current levels by the end of the century, respectively, represents a significant and imminent threat to aquatic biodiversity. The objective of this study was to assess the effects of acute short-term exposure to elevated temperature on the brain mitochondrial respiration of two Amazonian fish species with contrasting trophic roles: Schizodon fasciatus, which represents a prey species at a lower trophic level, and Pygocentrus nattereri, a predatory species. Specimens of Schizodon fasciatus and Pygocentrus nattereri were collected and subjected to temperatures of 28 °C and 37 °C for a period of four hours. Brain mitochondrial respiration was quantified to analyze complexes I, I + II, III, IV, proton leak (H⁺Leak), RCR, and ETS. Additionally, the production of reactive oxygen species (ROS) was evaluated. The results revealed that exposure to higher temperatures caused elevated complex I activity in both species, with a more pronounced increase observed in S. fasciatus. Furthermore, significant increases in complex I + II and complex III were observed in S. fasciatus, while complex IV showed a decrease in both species. H⁺Leak exhibited a decrease in P. nattereri, whereas RCR demonstrated an increase in both species. ROS production displayed a decrease in P. nattereri but remained stable in S. fasciatus. The findings suggest that both fish species possess the capacity to adapt their brain mitochondrial function to higher temperatures, albeit with species-specific responses. These adaptations assist in maintaining brain energy production and minimizing oxidative stress, and emphasize potential imbalances in predator-prey relationships under changing environmental conditions.