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First published online July 20, 2006
Journal of Experimental Biology 209, 2961-2970 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02319

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Cardiovascular and haematological responses of Atlantic cod (Gadus morhua) to acute temperature increase

M. J. Gollock^1,*, S. Currie², L. H. Petersen¹ and A. K. Gamperl¹

¹ Ocean Sciences Centre, Memorial University of Newfoundland, St John's, NL, A1C 5S7, Canada
² Biology Department, Mount Allison University, 63B York Street, Sackville, New Brunswick, E4L 1G, Canada

^* Author for correspondence at present address: Department of Biology, University of Ottawa, 150 Louis Pasteur, Ottawa, ON, K1N 6N5, Canada (e-mail: mgollock{at}uottawa.ca)

Accepted 9 May 2006

For fish to survive large acute temperature increases (i.e. >10.0°C) that may bring them close to their critical thermal maximum (CTM), oxygen uptake at the gills and distribution by the cardiovascular system must increase to match tissue oxygen demand. To examine the effects of an acute temperature increase (1.7°C h^-1 to CTM) on the cardiorespiratory physiology of Atlantic cod, we (1) carried out respirometry on 10.0°C acclimated fish, while simultaneously measuring in vivo cardiac parameters using Transonic® probes, and (2) constructed in vitro oxygen binding curves on whole blood from 7.0°C acclimated cod at a range of temperatures. Both cardiac output () and heart rate (fH) increased until near the fish's CTM (22.2±0.2°C), and then declined rapidly. Q₁₀ values for and fH were 2.48 and 2.12, respectively, and increases in both parameters were tightly correlated with O₂ consumption. The haemoglobin (Hb)-oxygen binding curve at 24.0°C showed pronounced downward and rightward shifts compared to 20.0°C and 7.0°C, indicating that both binding capacity and affinity decreased. Further, Hb levels were lower at 24.0°C than at 20.0°C and 7.0°C. This was likely to be due to cell swelling, as electrophoresis of Hb samples did not suggest protein denaturation, and at 24.0°C Hb samples showed peak absorbance at the expected wavelength (540 nm). Our results show that cardiac function is unlikely to limit metabolic rate in Atlantic cod from Newfoundland until close to their CTM, and we suggest that decreased blood oxygen binding capacity may contribute to the plateau in oxygen consumption.

Key words: Gadus morhua, temperature, cardiac output, heart rate, stroke volume, metabolic rate, haemoglobin, blood oxygen concentration

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