Temperature‐dependent changes in energy metabolism, intracellular pH and blood oxygen tension in the Atlantic cod

Abstract

The effect of acute increase in temperature on oxygen partial pressure (Po2) was measured in the gill arches of Atlantic cod Gadus morhua between 10 and 19° C by use of oxygen microoptodes. Oxygen saturation of the gill blood under control conditions varied between 90 and 15% reflecting a variable percentage of arterial or venous blood in accordance with the position of each optode in the gill arch. The data obtained suggested that arterial Po2 remained more or less constant and arterial oxygen uptake did not become limiting during warming. A progressive drop in venous Po2, however, was observed at >10° C indicating that excessive oxygen uptake from the blood is not fully compensated for by circulatory performance, until finally, Po2 levels fully collapse. In a second set of experiments energy and acid–base status of white muscle of Atlantic cod in vivo was measured by magnetic resonance (31P‐NMR) spectroscopy in unanaesthetized and unimmobilized fish in the temperature range between 13 and 21° C. A decrease in white muscle intracellular pH (pHi) with temperature occurred between 10 and 16° C (ΔpH per ° C = −0·025 per ° C). In white muscle temperature changes had no influence on high‐energy phosphates such as phosphocreatine (PCr) or ATP except during exposure to high critical temperatures (>16° C), indicating that white muscle energy status appears to be relatively insensitive to thermal stress if compared to the thermal sensitivity of the whole animal. The data were consistent with the hypothesis of an oxygen limitation of thermal tolerance in animals, which is set by limited capacity of oxygen supply mechanisms. In the case of Atlantic cod circulatory rather than ventilatory performance may be the first process to cause oxygen deficiency during heat stress.

Oxygen limited thermal tolerance in fish?

“…The maintenance of arterial P O 2 seen during warming in cod is in line with an excess capacity of the ventilatory system for oxygen uptake, if compared to oxygen distribution via circulation. However, arterial P O 2 fell drastically above 16 • C (Sartoris et al, 2003b), presumably indicating the temperature at which a minimum threshold P v,O 2 is reached in cod with the result of cardiac failure and organismic collapse.…”

“…They found that heart rate in rainbow trout decreased at temperatures above 24 • C, whereas ventilation remained virtually unchanged until death of the animals occurred. In cod implanted with micro-optodes in gill blood vessels, Sartoris et al (2003b) demonstrated that arterial oxygen tensions (P a,O 2 ) remained unaffected by progressive warming. However, venous oxygen tension (P v,O 2 ) dropped progressively during warming, in line with limited cardiac rather than ventilatory performance.…”

“…However, venous oxygen tension (P v,O 2 ) dropped progressively during warming, in line with limited cardiac rather than ventilatory performance. It was concluded that in resting cod at elevated temperatures, circulatory performance cannot fully compensate for excessive oxygen extraction from the blood Sartoris et al, 2003b). Functionally, this pattern can seriously hamper myocardial oxygen supply, as most teleost fish lack or only possess a weak coronary circulation and hence almost exclusively rely on the venous oxygen reserve to provide the heart with oxygen (Farrell, 1993).…”

Temperature and CO2additively regulate physiology, morphology and genomic responses of larval sea urchins,Strongylocentrotus purpuratus

“…For example, exposure to acidified sea water may act to lower the ceiling of organismal tolerance of high temperatures through changes in metabolism [4,17,18], whereas warmer temperatures may alter the permeability of cell membranes [19] and reduce the ability of organisms to regulate intracellular pH [20]. To explore the potential response of larval purple sea urchins to these co-occurring factors, we cultured larvae under conditions that mimicked future ocean change in the CCLME and assessed organismal performance across multiple levels of biological organization.…”

Muscle bioenergetics of speeding fish: In vivo 31P‐NMR studies in a 4.7 T MR scanner with an integrated swim tunnel

“…Peak position and signal integrals were analyzed using a specially adapted automatic fit routine as described in (21,22). Metabolite concentrations from peak integrals were calculated as described in (23). 4.…”