Exercise in the Cold: High Energy Turnover in Antarctic Fish
231
glycolytic capacity has been interpreted as a special adaptation to cold
environment [43]. However, since absence of lactate formation has only
been shown in notothenioids the question arises if indeed the low
glycolytic capacity has an adaptional value or if it is rather a special
phylogenetic trait of this fish family [9,44]. To shed light on this question
we investigated the effect of exhaustive exercise on an Antarctic
nonnotothenioid fish, the zoarcid Pachycara brachycephalum [45]. In this
benthic sluggish fish we found relatively high amounts of lactate
(11.5±O.7 J.lmol g-l muscle tissue), which is in the range found in flounder
acclimated to 11°C [46]. Based on these data, it may be concluded that a
low glycolytic capacity is not a general phenomenon in Antarctic fish.
Interestingly, we did not find significant amounts of lactate in the
plasma of P. brachycephalum after exhaustive exercise. In contrast to
mammals, the bulk of lactate is retained in the white musculature of fish
for glyconeogenesis in situ [47]. Nevertheless, significant increases in
lactate concentrations are found in the plasma after severe exercise in
temperate species. However, the muscle-to-blood gradient of lactate is
dependent on the acclimation temperature [38]. Cold acclimated trout had
lower blood lactate levels although intracellular concentrations were the
same in both groups. The authors explain this phenomenon by a reduction
of lactate diffusion from the intracellular space at low temperatures. It
should be noted, therefore, that in cold adapted fish the onset of anaerobic
metabolism must be established by the analysis of lactate levels in the
muscle tissue rather than in the plasma, as is frequently done in temperate
speCles.
Recovery from Exhaustive Exercise
During recovery from exhaustive exercise the restoration of pre-exercise
conditions must be achieved within reasonable time to enable successive
bouts of activity which may be crucial during predator-prey interactions.
Despite only partial cold compensation of locomotory performance in
fish, recovery processes seem to be largely independent of temperature
[38,48]. Metabolic recovery from escape swimming occurred at identical
rates in herring larvae reared at 5 and 12°C [48]. In trout
rephosphorylation of phosphocreatine and lactate clearance from blood
and muscle occurred at the same rates in fish acclimated to 5 and 18°C
[38]. This shows that although resting levels of oxygen consumption are
reduced in cold acclimated trout [49] the capacities for high power output
during exercise and for postexercise recovery metabolism are largely
compensated in cold acclimated animals. Again, the roach Rutilus ruti/us
231
glycolytic capacity has been interpreted as a special adaptation to cold
environment [43]. However, since absence of lactate formation has only
been shown in notothenioids the question arises if indeed the low
glycolytic capacity has an adaptional value or if it is rather a special
phylogenetic trait of this fish family [9,44]. To shed light on this question
we investigated the effect of exhaustive exercise on an Antarctic
nonnotothenioid fish, the zoarcid Pachycara brachycephalum [45]. In this
benthic sluggish fish we found relatively high amounts of lactate
(11.5±O.7 J.lmol g-l muscle tissue), which is in the range found in flounder
acclimated to 11°C [46]. Based on these data, it may be concluded that a
low glycolytic capacity is not a general phenomenon in Antarctic fish.
Interestingly, we did not find significant amounts of lactate in the
plasma of P. brachycephalum after exhaustive exercise. In contrast to
mammals, the bulk of lactate is retained in the white musculature of fish
for glyconeogenesis in situ [47]. Nevertheless, significant increases in
lactate concentrations are found in the plasma after severe exercise in
temperate species. However, the muscle-to-blood gradient of lactate is
dependent on the acclimation temperature [38]. Cold acclimated trout had
lower blood lactate levels although intracellular concentrations were the
same in both groups. The authors explain this phenomenon by a reduction
of lactate diffusion from the intracellular space at low temperatures. It
should be noted, therefore, that in cold adapted fish the onset of anaerobic
metabolism must be established by the analysis of lactate levels in the
muscle tissue rather than in the plasma, as is frequently done in temperate
speCles.
Recovery from Exhaustive Exercise
During recovery from exhaustive exercise the restoration of pre-exercise
conditions must be achieved within reasonable time to enable successive
bouts of activity which may be crucial during predator-prey interactions.
Despite only partial cold compensation of locomotory performance in
fish, recovery processes seem to be largely independent of temperature
[38,48]. Metabolic recovery from escape swimming occurred at identical
rates in herring larvae reared at 5 and 12°C [48]. In trout
rephosphorylation of phosphocreatine and lactate clearance from blood
and muscle occurred at the same rates in fish acclimated to 5 and 18°C
[38]. This shows that although resting levels of oxygen consumption are
reduced in cold acclimated trout [49] the capacities for high power output
during exercise and for postexercise recovery metabolism are largely
compensated in cold acclimated animals. Again, the roach Rutilus ruti/us