Hematocrit Is Associated with Thermal Tolerance and Modulated by Developmental Temperature in Juvenile Chinook Salmon

Abstract

To evaluate whether oxygen-carrying capacity influences thermal tolerance in fishes, we reared four Chinook salmon families in present-day (+0°C) and possible future (+4°C) temperatures and assessed the response of hematocrit (Hct) to acute temperature stress. In the +4°C treatment, Hct increased above control levels when juvenile fish were exposed to their critical thermal maximum (CT). Conversely, no effect of temperature stress on Hct was found in the +0°C treatment. Hct was positively associated with CT ([Formula: see text]; [Formula: see text]), contributing to the CT of the +4°C treatment being significantly higher than that of the +0°C treatment (mean ± SD, [Formula: see text] and [Formula: see text], respectively). The association between CT and Hct found here supports the hypothesis that thermal tolerance is affected by oxygen supply to tissue. Moreover, the developmental plasticity of CT and Hct could represent an adaptive mechanism for salmon faced with climate change.

Genetic variation for upper thermal tolerance diminishes within and between populations with increasing acclimation temperature in Atlantic salmon

“…Under a theory on thermal vulnerability, CT max is expected to correlate positively with hct (Portner et al 2017). This theory was supported by Muñoz et al (2018) who estimated higher CT max at higher acclimation temperatures in concert with higher hct and a positive phenotypic correlation between traits in Chinook salmon. However, we estimated partly the opposite: higher average CT max values at higher acclimation temperatures in concert with lower average hct values and negative phenotypic and genetic correlations between CT max and hct under colder acclimation temperature and none otherwise.…”

Acute and chronic cold exposure differentially affect cardiac control, but not cardiorespiratory function, in resting Atlantic salmon (Salmo salar)

“…Blood oxygen carrying capacity (i.e., Hct and Hb) and oxygen delivery to the tissues are generally considered to be large contributors to fish thermal tolerance, particularly at warm temperatures ( Anttila et al, 2013 ; Leeuwis et al, 2021 ; Muñoz et al, 2018 ; Pörtner and Knust, 2007 ; Pörtner, 2010 ; Wang and Overgaard, 2007 ). It is quite common for fish to release erythrocytes (red blood cells; RBCs) via splenic contraction within minutes of an acute stress as a secondary stress response ( Muñoz et al, 2018 ; Pearson and Stevens, 1991 ), and this results in an increase in Hct (i.e., in the number and/or in size of RBCs). However, this did not occur during our experiment.…”

The power struggle: assessing interacting global change stressors via experimental studies on sharks

“…Additionally, the increase in Hct at 31 °C may be associated with increases in hypoxia tolerance and thermal tolerance, which has been previously documented for blacktip reef sharks upon four weeks acclimation to 31°C 21 . Previous research in notothenioid fishes and Chinook salmon (Oncorhynchus tshawytscha) suggests that Hct is positively associated with critical thermal maximum, a thermal tolerance metric 28,29 . Further, as thermal tolerance and hypoxia tolerance are associated in blacktip reef sharks, an increase in Hct may further support the hypothesis of a common acclimation response and oxygen-dependent mechanism underlying these traits 3 .…”