Finally, our study shows that CTmax of adult zebrafish is oxygen-independent across a wide range of oxygen levels, and regardless of acclimation history.

Our second (fig A) testing CTmax at a wider range of oxygen levels showed significant effect of hyperoxia on CTmax of cold-acclimated fish, yet a third experiment (fig B) with larger sample size showed no effect. Our study shows that internal replication is vital as false significance may disappear.

Hyperoxia expands AS but offers no benefit during extreme acute warming. Only extreme hypoxia (30% air sat) reduces their warming tolerance.

Third, we expanded our sample size for fish acclimated to 14° and 20°C and assessed CTmax across the different oxygen levels.

Second, we acclimated zebrafish to 20, 28, and 34°C for 13–17 days, and tested their CTmax under acute oxygen exposure (30, 100, 200 % air sat).

First, we measured routine and maximum metabolic rates and CTmax of 20°C-acclimated fish across four oxygen levels: 50, 100, 150, and 250 % air saturation to investigate the relationship between water oxygen level and aerobic scope.

Because cold acclimation increases the density of mitochondria and can reduce gill surface area in some species, we hypothesized that cold acclimation can reduce the tolerance to acute warming through increased metabolic rate and reduced oxygen uptake capacity compared with control-acclimated fish.

Given the importance of thermal acclimation in modulating acute thermal limits, we investigated whether thermal acclimation impacts the oxygen dependence of Critical Thermal Maximum (CTmax) in adult zebrafish.

Studies manipulating water oxygen levels show mixed results, suggesting that the effect of oxygen availability on upper thermal limits is species and context-dependent.