Prevalence and mechanisms of environmental hyperoxia-induced thermal tolerance in fishes

Recent evidence has suggested environmental hyperoxia (O-2 supersaturation) can boost cardiorespiratory performance in aquatic ectotherms, thereby increasing resilience to extreme heat waves associated with climate change. Here, using rainbow trout (Oncorhynchus mykiss) as a model species, we analysed whether improved cardiorespiratory performance can explain the increased thermal tolerance of fish in hyperoxia (200% air saturation). Moreover, we collated available literature data to assess the prevalence and magnitude of hyperoxia-induced thermal tolerance across fish species. During acute warming, O-2 consumption rate was substantially elevated under hyperoxia relative to normoxia beyond 23 degrees C. This was partly driven by higher cardiac output resulting from improved cardiac contractility. Notably, hyperoxia mitigated the rise in plasma lactate at temperatures approaching upper limits and elevated the critical thermal maximum (+0.87 degrees C). Together, these findings show, at least in rainbow trout, that hyperoxia-induced thermal tolerance results from expanded tissue O-2 supply capacity driven by enhanced cardiac performance. We show 50% of the fishes so far examined have increased critical thermal limits in hyperoxia (range: 0.4-1.8 degrees C). This finding indicates environmental hyperoxia could improve the ability of a large number of fishes to cope with extreme acute warming, thereby increasing resilience to extreme heat wave events resulting from climate change.

Automated summary

Recent evidence suggests that environmental hyperoxia can enhance cardiorespiratory performance and increase thermal tolerance in fish, helping them cope with extreme heat waves caused by climate change. This effect is mainly due to improved cardiac function and increased tissue oxygen supply capacity. Additionally, available literature data show that hyperoxia can improve thermal tolerance in a large number of fish species.