In a marine teleost, the significance of oxygen supply for acute thermal tolerance depends upon the context and the endpoint used

Abstract

Eight juvenile European seabass were exposed to two thermal ramping protocols with different levels of aerobic activity and tolerance endpoint: the critical thermal maximum for swimming (CTSmax) while exercising aerobically until fatigue, and the critical thermal maximum (CTmax) under static conditions until loss of equilibrium (LOE). In the CTSmax, warming caused a profound increase in oxygen uptake rate (M˙O2) culminating in a gait transition, from steady aerobic towards unsteady anaerobic swimming, then fatigue at 30.3±0.4°C (mean±SE). Gait transition and fatigue presumably indicate an oxygen limitation, an inability to meet the combined demands of swimming plus warming. The CTmax also elicited an increase in M˙O2, culminating in LOE at 34.0±0.4°C, significantly warmer than fatigue at CTSmax. The maximum M˙O2 achieved in the CTmax was, however, less than 30% of that achieved in the CTSmax. Therefore, the static CTmax did not exploit full cardiorespiratory capacity for oxygen supply, indicating that LOE was not caused by systemic oxygen limitation. Consequently, systemic oxygen supply can be significant for tolerance of acute warming in seabass but this depends upon the physiological context and the endpoint used.

Physiological responses to acute warming at the agitation temperature in a temperate shark

“…Thus, an oxygen limitation of the agitation temperature in dogfish is not apparent from these data; although, effects of hypoxia on the agitation temperature have been documented in other fishes (McDonnell et al, 2019(McDonnell et al, , 2021Potts et al, 2021). Therefore, these data suggest that dogfish do not increase their reliance on anaerobic metabolic pathways at the agitation temperature when at rest, but may do so with further warming to CT max or when swimming (Nati et al, 2023;Sandrelli and Gamperl, 2023). Dogfish exhibited signs of thermal cellular stress at the agitation temperature.…”

Respiratory acidosis and O2 supply capacity do not affect the acute temperature tolerance of rainbow trout (Oncorhynchus mykiss)

“…The OCLTT hypothesis would therefore predict that changes in environmental O 2 and CO 2 levels would affect the thermal tolerance limits of fish via direct impacts on the O 2 supply capacity of ectotherms ( Pörtner et al., 2017 ). However, studies to date have not universally supported the OCLTT hypothesis, with impacts of environmental hypoxia and hyperoxia ( Devor et al., 2016 ; Ern et al., 2016 ; Giomi et al., 2019 ; Islam et al., 2020 ; Leeuwis et al., 2021 ; Andreassen et al., 2022 ; McArley et al., 2022a ; Nati et al., 2023 ), chronic high CO 2 , and direct manipulations of physiological O 2 supply capacity ( Brijs et al., 2015 ) showing species-specific effects on temperature tolerance. A recent review has highlighted that complex inter-related physiological systems could determine the upper thermal tolerance limits of fish ( Ern et al., 2023 ) and suggests several alternative underlying mechanisms that may determine the critical thermal maximum (CT max ).…”