The effect of gradually increased water temperature on the metabolism of temperate eelpout from the North Sea (Zoarces viviparus) and Antarctic eelpout (Pachycara brachycephalum) was investigated. Standard metabolic rate (SMR) was similar in cold-adapted P. brachycephalum and cold-acclimated Z. viviparus in the low temperature range. This indicates that Antarctic eelpout show no metabolic cold adaptation (as originally defined by Wohlschlag); however, they do show a compensatory increase of oxygen consumption compared to warm-acclimated eelpout. SMR increased more strongly with rising temperature in P. brachycephalum than in Z. viviparus, which is reflected in a higher Arrhenius activation energy for oxygen consumption (99+/−5 kJ mol(−)(1), versus 55+/−3 kJ mol(−)(1) for cold-acclimated Z. viviparus; means +/− s.d.). The intracellular pH in the white musculature of Z. viviparus follows alphastat regulation over the whole investigated temperature range and dropped at a rate of −0.016 pH units per degrees C between 3 degrees C and 24 degrees C. In Antarctic eelpout white muscle pH declined at a rate of −0.015 pH units per degrees C between 0 degrees C and 3 degrees C, but deviated from alphastat at higher temperatures, indicating that thermal stress leads to acid-base disturbances in this species. The upper critical temperature limit (Tc(II); characterised by a transition to anaerobic metabolism) was found to be between 21 degrees C and 24 degrees C for Z. viviparus and around 9 degrees C for P. brachycephalum. In both species a rise of succinate concentration in the liver tissue turned out to be the most useful indicator of Tc(II). Obviously, liver is more sensitive to heat stress than is white muscle. Accordingly, the energy status of white muscle is not diminished at Tc(II). Heat-induced hyperglycaemia was observed in Antarctic eelpout (at 9 degrees C and 10 degrees C), but not in common eelpout. Based on our results and on literature data, impaired respiration in combination with circulatory failure is suggested as the final cause of heat death. Our data suggest that the southern distribution limit of Zoarces viviparus is correlated with the limit of thermal tolerance. Therefore, it can be anticipated that global warming would cause a shift in the distribution of this species.

Baldwin
J.
(
1971
).
Adaptation of enzymes to temperature: acetylcholinesterase in the central nervous system of fishes
.
Comp. Biochem. Physiol
40
,
181
–.
Baldwin
J.
,
Hochachka
P. W.
(
1970
).
Functional significance of isoenzymes in thermal acclimation: acetylcholinesterase from trout brain
.
Biochem. J
116
,
883
–.
Beamish
F. W. H.
(
1963
).
Seasonal changes in the standard rate of oxygen consumption of fishes
.
Can. J. of Zool
42
,
177
–.
Clarke
A.
(
1991
).
What is cold adaptation and how should we measure it?
.
Am. Zool
31
,
81
–.
Friedlander
M. J.
,
Kotchabhakdi
N.
,
Prosser
C. L.
(
1976
).
Effects of cold and heat on behaviour and cerebellar function in goldfish
.
J. Comp. Physiol
112
,
19
–.
Grieshaber
M. K.
,
Hardewig
I.
,
Kreutzer
U.
,
Pörtner
H. O.
(
1994
).
Physiological and metabolic responses to hypoxia in invertebrates
.
Rev. Physiol. Biochem. Pharmacol
125
,
43
–.
Johnston
I. A.
,
Bernard
L. M.
(
1983
).
Utilization of the ethanol pathway in carp following exposure to anoxia
.
J. Exp. Biol
104
,
73
–.
Kammermeier
H.
(
1987
).
High energy phosphate of the myocardium: contraction versus free energy change
.
Basic Res. Cardiol
82
,
2
–.
Leach
G. J.
,
Taylor
M. H.
(
1980
).
The role of cortisol in stress-induced metabolic changes in Fundulus heteroclitus
.
Gen. Comp. Endocrinol
42
,
219
–.
McDonald
D. G.
(
1983
).
Interaction of environmental calcium and low pH on the physiology of the rainbow trout, Salmo gairdneri. I. Branchial and renal net ion and H+fluxes
.
J. Exp. Biol
102
,
123
–.
Mohnen
V. A.
,
Wang
W. C.
(
1992
).
An overview of global warming
.
Environm. Tox. Chem
11
,
1051
–.
Pörtner
H. O.
,
Boutilier
R. G.
,
Tang
Y.
,
Toews
D. P.
(
1990
).
Determination of intracellular pH and P COafter metabolic inhibition by fluoride and nitrilotriacetic acid
.
Respir. Physiol
81
,
255
–.
Pörtner
H. O.
,
Finke
E.
,
Lee
P. G.
(
1996
).
Effective Gibb's free energy change of ATP hydrolysis and metabolic correlates of intracellular pH in progressive fatigue of squid (Lolliguncula brevis) mantle muscle
.
Am. J. Physiol
271
,
1403
–.
Reeves
R. B.
(
1972
).
An imidazole alphastat hypothesis for vertebrate acid-base regulation: Tissue carbon dioxide content and body temperature in bullfrogs
.
Resp. Physiol
14
,
219
–.
Ryan
S. N.
(
1995
).
The effect of chronic heat stress on cortisol levels in the Antarctic fish Pagothenia borchgrevinki
.
Experientia
51
,
768
–.
Somero
G. N.
,
DeVries
A. L.
(
1967
).
Temperature tolerance of some Antarctic fishes
.
Science
156
,
257
–.
Staurnes
M.
,
Rainuzzo
J. R.
,
Sigholt
T.
,
Jorgensen
L.
(
1994
).
Acclimation of atlantic cod (Gadus morhua) to cold water: stress response, osmoregulation, gill lipid composition and gill Na+-K+-ATPase activity
.
Comp. Biochem. Physiol
109
,
413
–.
Teague
W. E.
,
Dobson
G. P.
(
1992
).
Effect of temperature on the creatine kinase equilibrium
.
J. Biol. Chem
267
,
14084
–.
Tewari
Y. B.
,
Goldberg
R. N.
,
Advani
J. V.
(
1991
).
Thermodynamics of the disproportionation of adenosine 5-diphosphate to adenosine 5 -triphosphate and adenosine 5-monophosphate. II. Experimental data
.
Biophys. Chem
40
,
263
–.
Torres
J. J.
,
Somero
G. N.
(
1988
).
Vertical distribution and metabolism in antarctic mesopelagic fishes
.
Comp. Biochem. Physiol
90
,
521
–.
van Dijk
P. L. M.
,
Hardewig
I.
,
Pörtner
H. O.
(
1997
).
Temperature-dependent shift of pHiin fish white muscle: contributions of passive and active processes
.
Am. J. Physiol
272
,
84
–.
Wells
R. M.
(
1987
).
Respiration of Antarctic fish from McMurdo Sound
.
Comp. Biochem. Physiol
88
,
417
–.
Wohlschlag
D. E.
(
1963
).
An Antarctic fish with unuasually low metabolism
.
Ecology
44
,
557
–.
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