Hyperoxia Does Not Extend Critical Thermal Maxima (CTmax) in White- or Red-Blooded Antarctic Notothenioid Fishes

AbstractUnderstanding what limits the capacity of organisms to tolerate increasing temperatures is a critical objective in comparative biology. Using an experimental system of Antarctic notothenioid fishes, we sought to determine whether a mismatch between oxygen demand and oxygen supply was responsible for setting thermal tolerance limits. Previous studies have shown that Antarctic icefishes (family Channichthyidae), which lack hemoglobin, have lower critical thermal maxima (CTmax) than red-blooded notothenioids collected from the same region of the Antarctic (Western Antarctic Peninsula). In addition, within the notothenioid fishes there exists a positive correlation between CTmax and hematocrit. We tested the hypothesis that the lower CTmax of icefishes is associated with reduced oxygen supply. We employed an experimental heat ramp (4°C h−1) to determine CTmax under both normoxic and hyperoxic conditions and quantified correlates of oxygen limitation (lactate levels and expression of hypoxia-inducible ...