Smalleye Pacific opah and swordfish can conserve metabolic heat and maintain specific body regions warmer than ambient water temperature (i.e., regional heterothermy). Consequently, blood-O2 uptake at the gills occurs at the environmental temperature at which the individual is found, but O2 offloading will occur at different temperatures in different tissues. While several regionally heterothermic fishes (e.g., billfishes, tunas, and sharks) show a reduced temperature effect on haemoglobin (Hb)-O2 affinity, the temperature-dependence of Hb-O2 affinity in opah and swordfish is unknown. We hypothesized that the Hb of opah and swordfish would also show a reduced temperature-dependence. Opah whole blood-O2 affinity exhibited a reverse temperature-dependence above 50% Hb-O2 saturation (10–20°C, pH 7.2–8.0), while the temperature-dependence of swordfish blood-O2 affinity (10–25°C) was saturation and pH dependent, becoming temperature-independent below 50% Hb-O2 saturation and pH 7.4. Experiments on stripped haemolysates showed that adding ATP ([ATP]/[Hb]=30) decreased the temperature sensitivity of Hb-O2 affinity, changing the overall oxygenation enthalpy (ΔH') values of opah (10–20°C) and swordfish (10–25°C) Hbs at pH 7.4 from -15 and -42 kJ mol−1 O2, respectively, to +84 and -9 kJ mol−1 O2. Swordfish blood-O2 affinity was high compared to other large, pelagic, marine teleosts, which may be due to unusually low ATP/Hb levels, but might also enable swordfish to forage in the potentially low-oxygenated water of the upper reaches of the oxygen minimum layer. The existence of Hbs with reduced temperature sensitivity in regionally heterothermic fishes may prevent marked changes in Hb-O2 affinity between the cold and warm tissues.
Temperature independence of haemoglobin-oxygen affinity in smalleye Pacific opah (Lampris incognitus) and swordfish (Xiphias gladius)
Present address: Biology Department and Department of Resource Management and Protection, Vancouver Island University, Nanaimo, BC V9R 5S5, Canada
- Award Group:
- Funder(s): National Science Foundation
- Award Id(s): 1354593
- Funder(s):
- Award Group:
- Funder(s): Natural Sciences and Engineering Research Council of Canada
- Award Id(s): 261924-13
- Funder(s):
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Phillip R. Morrison, Diego Bernal, Chugey A. Sepulveda, Nicholas C. Wegner, Colin J. Brauner; Temperature independence of haemoglobin-oxygen affinity in smalleye Pacific opah (Lampris incognitus) and swordfish (Xiphias gladius). J Exp Biol 2022; jeb.243820. doi: https://doi.org/10.1242/jeb.243820
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