Venous hemodynamic responses to acute temperature increase in the rainbow trout ( Oncorhynchus mykiss )

SUMMARYAn insufficient supply of oxygen under thermal stress is thought to define thermal optima and tolerance limits in teleost fish. When under thermal stress, cardiac function plays a crucial role in sustaining adequate oxygen supply for respiring tissues. Thus, adaptive phenotypic plasticity of cardiac performance may be critical for modifying thermal limits during temperature acclimation. Here we investigated effects of temperature acclimation on oxygen consumption, cardiac function and blood oxygen carrying capacity of a eurythermal goby fish, Gillichthys mirabilis, acclimated to 9, 19 and 26°C for 4weeks. Acclimation did not alter resting metabolic rates or heart rates; no compensation of rates was observed at acclimation temperatures. However, under an acute heat ramp, warm-acclimated fish exhibited greater heat tolerance (CT max =33.3, 37.1 and 38.9°C for 9°C-, 19°C-and 26°C-acclimated fish, respectively) and higher cardiac arrhythmia temperatures compared with 9°C-acclimated fish. Heart rates measured under an acute heat stress every week during 28days of acclimation suggested that both maximum heart rates and temperature at onset of maximum heart rates changed over time with acclimation. Hemoglobin levels increased with acclimation temperature, from 35gl −1 in 9°C-acclimated fish to 60-80gl −1 in 19°C-and 26°C-acclimated fish. Oxygen consumption rates during recovery from acute heat stress showed post-stress elevation in 26°C-acclimated fish. These data, coupled with elevated resting metabolic rates and heart rates at warm temperatures, suggest a high energetic cost associated with warm acclimation in G. mirabilis. Furthermore, acclimatory capacity appears to be optimized at 19°C, a temperature shown by behavioral studies to be close to the speciesʼ preferred temperature. Supplementary material available online at

Section: Metabolic Rate During Recovery From An Acute Thermal Stressmentioning

confidence: 67%

Section: Introductionmentioning

confidence: 99%

Physiological plasticity of cardiorespiratory function in a eurythermal marine teleost, the longjaw mudsucker,Gillichthys mirabilis

Jayasundara

Somero

2013

“…Interpreting Ca O2 data during warming is more complex because of potential pH and temperature effects on the Hb-oxygen affinity curve, and because warming has variable effects on blood [Hb] (Taylor et al, 1997;Farrell, 1997;Sandblom and Axelsson, 2007). Even so, Ca O2 was maintained in resting sockeye salmon warmed to T crit as well as in exercising sockeye salmon warmed above T opt (Steinhausen et al, 2008).…”

Section: The Fry Curve For Aerobic Scopementioning

confidence: 99%

“…Warming increases cardiac output solely by increasing heart rate. This is true for both resting and exercising salmonids (Sandblom and Axelsson, 2007;Clark et al, 2008a;Steinhausen et al, 2008), presumably through a direct temperature effect on the cardiac pacemaker rate (Randall, 1970). However, because fish have a maximum heart rate (Farrell, 1991) and heart rate is already elevated by the exercise, the maximum heart rate must be reached at a temperature well below that for resting fish (Steinhausen et al, 2008).…”

Section: The Fry Curve For Aerobic Scopementioning

confidence: 99%

Environment, antecedents and climate change: lessons from the study of temperature physiology and river migration of salmonids

Farrell

2009

240

217

SummaryAnimal distributions are shaped by the environment and antecedents. Here I show how the temperature dependence of aerobic scope (the difference between maximum and minimum rates of oxygen uptake) is a useful tool to examine the fundamental temperature niches of salmonids and perhaps other fishes. Although the concept of aerobic scope has been recognized for over half a century, only recently has sufficient evidence accumulated to provide a mechanistic explanation for the optimal temperature of salmonids. Evidence suggests that heart rate is the primary driver in supplying more oxygen to tissues as demand increases exponentially with temperature. By contrast, capacity functions (i.e. cardiac stroke volume, tissue oxygen extraction and haemoglobin concentration) are exploited only secondarily if at all, with increasing temperature, and then perhaps only at a temperature nearing that which is lethal to resting fish. Ultimately, however, heart rate apparently becomes a weak partner for the cardiorespiratory oxygen cascade when temperature increases above the optimum for aerobic scope. Thus, the upper limit for heart rate may emerge as a valuable, but simple predictor of optimal temperature in active animals, opening the possibility of using biotelemetry of heart rate in field situations to explore properly the full interplay of environmental factors on aerobic scope. An example of an ecological application of these physiological discoveries is provided using the upriver migration of adult sockeye salmon, which have a remarkable fidelity to their spawning areas and appear to have an optimum temperature for aerobic scope that corresponds to the river temperatures experienced by their antecedents. Unfortunately, there is evidence that this potential adaptation is incompatible with the rapid increase in river temperature presently experienced by salmon as a result of climate change. By limiting aerobic scope, river temperatures in excess of the optimum for aerobic scope directly impact upriver spawning migration and hence lifetime fecundity. Thus, use of aerobic scope holds promise for scientists who wish to make predictions on how climate change may influence animal distributions.

“…However, it is well known that acute exposure to high temperatures results in depression of cardiac output (Gollock et al, 2006;Sandblom and Axelsson, 2007;Steinhausen et al, 2008), possibly due to temperature-related changes in electrical excitability. Since stroke volume is fairly insensitive to temperature increases, modulation of cardiac output is achieved by temperatureinduced changes in f H .…”

Section: Introductionmentioning

confidence: 99%

Effects of seasonal acclimatization on temperature-dependence of cardiac excitability in the roach, Rutilus rutilus

Badr

El-Sayed

Vornanen

2016

Temperature sensitivity of electrical excitability is a potential limiting factor for performance level and thermal tolerance of excitable tissues in ectothermic animals. To test whether the rate and rhythm of the heart acclimatize to seasonal temperature changes, thermal sensitivity of cardiac excitation in a eurythermal teleost, the roach (Rutilus rutilus), was examined. Excitability of the heart was determined from in vivo electrocardiograms and in vitro microelectrode recordings of action potentials (APs) from winter and summer roach acclimatized to 4 and 18°C, respectively. Under heat ramps (3°C h −1 ), starting from the acclimatization temperatures of the fish, heart rate increased to maximum values of 78±5 beats min −1 (at 19.8±0.5°C) and 150±7 beats min −1 (at 28.1±0.5°C) for winter and summer roach, respectively, and then declined in both groups. Below 20°C, heart rate was significantly higher in winter than in summer roach (P<0.05), indicating positive thermal compensation. Cardiac arrhythmias appeared with rising temperature as missing QRS complexes, increase in variability of heart rate, episodes of atrial tachycardia, ventricular bradycardia and complete cessation of the heartbeat (asystole) in both winter and summer roach. Unlike winter roach, atrial APs of summer roach had a distinct early repolarization phase, which appeared as shorter durations of atrial AP at 10% and 20% repolarization levels in comparison to winter roach (P<0.05). In contrast, seasonal acclimatization had only subtle effects on ventricular AP characteristics. Plasticity of cardiac excitation appears to be necessary for seasonal improvements in performance level and thermal resilience of the roach heart.