Research on sablefish (Anoplopoma fimbria) suggests that limited capacity to increase heart function leaves hypoxic fish susceptible to heat waves

Abstract

Studies of heart function and metabolism have been used to predict the impact of global warming on fish survival and distribution, and their susceptibility to acute and chronic temperature increases. Yet, despite the fact that hypoxia and high temperatures often co-occur, only one study has examined the effects of hypoxia on fish thermal tolerance, and the consequences of hypoxia for fish cardiac responses to acute warming have not been investigated. We report that sablefish ( Anoplopoma fimbria ) did not increase heart rate or cardiac output when warmed while hypoxic, and that this response was associated with reductions in maximum O 2 consumption and thermal tolerance (CT max ) of 66% and approximately 3°C, respectively. Further, acclimation to hypoxia for four to six months did not substantially alter the sablefish's temperature-dependent physiological responses or improve its CT max . These results provide novel, and compelling, evidence that hypoxia can impair the cardiac and metabolic response to increased temperatures in fish, and suggest that some coastal species may be more vulnerable to climate change-related heat waves than previously thought. Further, they support research showing that cross-tolerance and physiological plasticity in fish following hypoxia acclimation are limited.

Temperature effects on the contractile performance and efficiency of oxidative muscle from a eurythermal versus a stenothermal salmonid

“…Nonetheless, it is very likely that: (1) the inefficiency of myocardial respiration in char (present study; Penney et al, 2014 ); (2) the ability of salmon, but not char, to enhance myocardial contraction efficiency at 20 versus 15°C; (3) the increased work required to lengthen the char myocardium following warm acclimation; and (4) the constrained upper myocardial contraction frequency (consistent with Penney et al, 2014 : salmon ∼134 beats min −1 ; char ∼116 beats min −1 ) would limit cardiac performance at higher temperatures in char. This conclusion is consistent with numerous studies showing that cardiac function is a key determinant of the maximum temperatures at which fish can survive ( Wang and Overgaard, 2007 ; Farrell et al, 2009 ; Eliason et al, 2011 ; Franklin et al, 2013 ; Iftikar and Hickey, 2013 ; Eliason and Anttila, 2017 ; Christen et al, 2018 ; Leeuwis et al, 2021 ). Whether the difference in maximum heart (contraction) rate between char and salmon is related to interspecific differences in pacemaker properties, or to how temperature affects the ability of char ventricular myocytes to maintain ion fluxes and myocardial excitability, would be interesting to examine given the findings of Haverinen and Vornanen (2020) .…”

Can temperature-dependent changes in myocardial contractility explain why fish only increase heart rate when exposed to acute warming?

“…When exposed to an acute rise in temperature, fish increase cardiac output (Q) in an attempt to meet their increased demands for oxygen (metabolic rate), a response that is mediated almost exclusively by increases in heart rate (f H ). However, increases in f H cannot carry on indefinitely, and at a certain point f H plateaus before becoming arrhythmic and dropping back to resting levels just prior to the fish's upper critical temperature (T crit ) (Farrell et al, 1996;Farrell, 2009;Gollock et al, 2006;Leeuwis et al, 2021;Steinhausen et al, 2008;Verhille et al, 2013). Research indicates (Oncorhynchus mykiss) at temperatures from 10 to 16 o C, and this may constrain V S , in particular as the period of cardiac relaxation (diastolic filling) also decreases as the heart beats faster.…”

Marine Heatwaves Exceed Cardiac Thermal Limits of Adult Sparid Fish (Diplodus capensis, Smith 1884)

“…These findings suggest that if adult D. capensis average T ARR is fixed (hard-upper cardiac limit to thermal tolerance; Morgan et al, 2021), they may not survive this scenario, as water temperatures extend beyond the average T ARR . Furthermore, they may not be able to adapt in pace with climate warming, suggesting low potential for evolutionary rescue (Doyle et al, 2011;Klerks et al, 2019;Leeuwis et al, 2021). Adult D. capensis may therefore be living at the edge of their upper thermal cardiac limits, with temperature peaks that exceed physiological limits and could cause hypoxia (Leeuwis et al, 2021) resulting in high mortality (Deutsch et al, 2008;Huey et al, 2012;Genin et al, 2020).…”