Coastal marine fishes can combat ocean deoxygenation through respiratory plasticity

Climate change is increasing the occurrence and severity of marine hypoxia events worldwide. Hypoxia can impact marine fishes by constraining O 2 uptake and reducing the energy available for vital and non-vital functions. Here, we explored the hypothesis that the red drum ( Sciaenops ocellatus ) – an economically valuable species native to the coastal estuaries of the Gulf of Mexico – was capable of respiratory and metabolic plasticity that would mitigate the effects of hypoxia. Through a series of studies, we demonstrated that juvenile red drum exposed to hypoxia for up to 42 days exhibited significant plasticity that improved oxygen uptake affinity, tissue oxygen utilization efficiency and anaerobic capacity. Specifically, red blood cells exhibited dynamic transcriptional regulation of specific hemoglobin isoforms that correlated with reduced pH sensitivity and an overall increase in oxygen affinity. Furthermore, red muscle mitochondria exhibited improved OXPHOS control ratios and control efficiency, effectively allowing a greater amount of ATP to be generated per unit oxygen. These findings coincided with reduce hypoxia vulnerability (i.e. reduced critical oxygen thresholds) and higher maximum metabolic rates when tested in hypoxia, as well as a significant increase in anaerobic burst swimming capacity. Interestingly, there was no improvement in maximum metabolic rate when tested in normoxia. This is consistent with the notion that oxygen supply capacity reaches a plateau at higher oxygen tensions – a finding validated here for red drum by employing a hyperoxia exposure during maximum metabolic rate determination. Interestingly, embryonic red drum exposed to hypoxia during the first 72 hours post-fertilization and then reared to post-metamorphosis in normoxia also exhibited significant respiratory plasticity, but of an opposing nature. Contrary to expectations, hypoxia exposed embryonic fish showed compromised hypoxia vulnerability and elevated maximum metabolic rate when tested in normoxic environments, indicative of improved capacity for oxygen transport and utilization coincident with reduced respiratory system affinity. Overall, these data suggest that coastal marine species that commonly experience hypoxic events, such as red drum, have the capacity for respiratory plasticity that can mitigate the effects of hypoxia. However, the significance of this plasticity and how it can shape organismal outcomes can differ based on life stage. Funding for this work was provided by the National Science Foundation. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.