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Fish cardiorespiratory physiology in an era of climate change

Citation

Farrell, AP and Eliason, EJ and Sandblom, E and Clark, TD, Fish cardiorespiratory physiology in an era of climate change, Canadian Journal of Zoology, 87, (10) pp. 835-851. ISSN 0008-4301 (2009) [Refereed Article]

DOI: doi:10.1139/Z09-092

Abstract

This review examines selected areas of cardiovascular physiology where there have been impressive gains of knowledge and indicates fertile areas for future research. Because arterial blood is usually fully saturated with oxygen, in-creasing cardiac output is the only means for transferring substantially more oxygen to tissues. Consequently, any behavioural or environmental change that alters oxygen uptake typically involves a change in cardiac output, which in fishes can amount to a threefold change. During exercise, not all fishes necessarily have the same ability as salmonids to increase cardiac output by increasing stroke volume; they rely more on increases in heart rate instead. The benefits associated with increasing cardiac output via stroke volume or heart rate are unclear. Regardless, all fishes examined so far show an exquisite cardiac sensitivity to filling pressure and the cellular basis for this heightened cardiac stretch sensitivity in fish is being unraveled. Even so, a fully integrated picture of cardiovascular functioning in fishes is hampered by a dearth of studies on venous circulatory control. Potent positive cardiac inotropy involves stimulation of sarcolemmal b-adrenoceptors, which in-creases the peak trans-sarcolemmal current for calcium and the intracellular calcium transient available for binding to troponin C. However, adrenergic sensitivity is temperature-dependent in part through effects on membrane currents and receptor density. The membrane currents contributing to the pacemaker action potential are also being studied but remain a prime area for further study. Why maximum heart rate is limited to a low rate in most fishes compared with similar-sized mammals, even when Q10 effects are considered, remains a mystery. Fish hearts have up to three oxygen supply routes. The degree of coronary capillarization circulation is of primary importance to the compact myocardium, unlike the spongy myocardium, where venous oxygen partial pressure appears to be the critical factor in terms of oxygen delivery. Air-breathing fishes can boost the venous oxygen content and oxygen partial pressure by taking an air breath, thereby providing a third myocardial oxygen supply route that perhaps compensates for the potentially precarious supply to the spongy myocardium during hypoxia and exercise. In addition to venous hypoxemia, acidemia and hyperkalemia can ac-company exhaustive exercise and acute warming, perhaps impairing the heart were it not for a cardiac protection mecha-nism afforded by b-adrenergic stimulation. With warming, however, a mismatch between an animalís demand for oxygen (a Q10 effect) and the capacity of the circulatory and ventilatory systems to delivery this oxygen develops beyond an optimum temperature. At temperature extremes in salmon, it is proposed that detrimental changes in venous blood composition, coupled with a breakdown of the cardiac protective mechanism, is a potential mechanism to explain the decline in maximum and cardiac arrhythmias that are observed. Furthermore, the fall off in scope for heart rate and cardiac output is used to explain the decrease in aerobic scope above the optimum temperature, which may then explain the field observation that adult sockeye salmon (Oncorhynchus nerka (Walbaum in Artedi, 1792)) have difficulty migrating to their spawning area at temperatures above their optimum. Such mechanistic linkages to lifetime fitness, whether they are cardiovascular or not, should assist with predictions in this era of global climate change.

Item Details

Item Type:Refereed Article
Research Division:Biological Sciences
Research Group:Zoology
Research Field:Animal Behaviour
Objective Division:Environment
Objective Group:Flora, Fauna and Biodiversity
Objective Field:Coastal and Estuarine Flora, Fauna and Biodiversity
UTAS Author:Clark, TD (Dr Timothy Clark)
ID Code:103421
Year Published:2009
Web of Science® Times Cited:92
Deposited By:IMAS Research and Education Centre
Deposited On:2015-10-08
Last Modified:2015-10-08
Downloads:0

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