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C. Zimmermann and G. Hubold
representative for the benthic life style of the adult specimens [26]. In
addition to the general ordination, intraspecific effects of body mass or age
can be derived from Fig. 4. For Myoxocephalus and Pagothenia there are
indications for a correlation between activity and size - surprisingly in
opposite directions: younger Pagothenia are more active than older ones,
the opposite is true for Myoxocephalus. A reduction of activity with
increasing age is also known for Boreogadus [29], Pagothenia 's ecological
equivalent in the Arctic [30], and for a number of species from lower
Aritarctic latitudes [13]. This ontogenetic activity shift should also be
considered for the comparison of metabolic rates between species.
Conclusions
The results of this study show that within the limited range of polar ocean
temperatures, the standard oxygen consumption is mostly dependent on the
fish's potential activity (as a measure for its "mode of life"). In contrast,
differences are much less related to the direct effects of the environmental
temperature. Temperature effects on fish metabolism can only be
determined when the predominant influence of the mode of life, includjng
differences in ontogenetic activity, is identified and eliminated in the
experimental set-up, or if a wide temperature range is used. The still
unresolved question of different metabolic performance of tropical,
temperate and polar fishes can be only answered when truly comparable
fishes of the same ecological profile are compared in carefully designed,
low-stress experiments.
Therefore, the knowledge of a fish's ecotype and activity pattern is
essential for a reasonable comparison of metabolic rates. This was not
always taken into account in previous investigations, resulting in
contradictions about the adaptations of polar fish.
The determination of a fish's life style is hardly possible without a
careful recording of its spontaneous activity. On the other hand, the
evaluation of a fish's activity might even provide us with a parametric
measure for "mode of life," which was so far not quantifiable. For this
purpose we propose to use the quotient of maximum and mean movement
rate, which is easy to determine and avoids - as a ratio - difficulties due to
different set-ups used for a movement detection.
Acknowledgments
The critical comments ofD. Piepenburg, C. Krembs, W Hagen and an anonymous
referee improved the manuscript significantly. Thanks are due to A. L. DeVries,
who made the stay of C.Z. at the US McMurdo Station possible. Part of this work
was supported by the Deutsche Forschungsgemeinschaft (DFG Hu 46112-1 to
G.H.) and the National Science Foundation (S-005 to A.L. DeVries).
C. Zimmermann and G. Hubold
representative for the benthic life style of the adult specimens [26]. In
addition to the general ordination, intraspecific effects of body mass or age
can be derived from Fig. 4. For Myoxocephalus and Pagothenia there are
indications for a correlation between activity and size - surprisingly in
opposite directions: younger Pagothenia are more active than older ones,
the opposite is true for Myoxocephalus. A reduction of activity with
increasing age is also known for Boreogadus [29], Pagothenia 's ecological
equivalent in the Arctic [30], and for a number of species from lower
Aritarctic latitudes [13]. This ontogenetic activity shift should also be
considered for the comparison of metabolic rates between species.
Conclusions
The results of this study show that within the limited range of polar ocean
temperatures, the standard oxygen consumption is mostly dependent on the
fish's potential activity (as a measure for its "mode of life"). In contrast,
differences are much less related to the direct effects of the environmental
temperature. Temperature effects on fish metabolism can only be
determined when the predominant influence of the mode of life, includjng
differences in ontogenetic activity, is identified and eliminated in the
experimental set-up, or if a wide temperature range is used. The still
unresolved question of different metabolic performance of tropical,
temperate and polar fishes can be only answered when truly comparable
fishes of the same ecological profile are compared in carefully designed,
low-stress experiments.
Therefore, the knowledge of a fish's ecotype and activity pattern is
essential for a reasonable comparison of metabolic rates. This was not
always taken into account in previous investigations, resulting in
contradictions about the adaptations of polar fish.
The determination of a fish's life style is hardly possible without a
careful recording of its spontaneous activity. On the other hand, the
evaluation of a fish's activity might even provide us with a parametric
measure for "mode of life," which was so far not quantifiable. For this
purpose we propose to use the quotient of maximum and mean movement
rate, which is easy to determine and avoids - as a ratio - difficulties due to
different set-ups used for a movement detection.
Acknowledgments
The critical comments ofD. Piepenburg, C. Krembs, W Hagen and an anonymous
referee improved the manuscript significantly. Thanks are due to A. L. DeVries,
who made the stay of C.Z. at the US McMurdo Station possible. Part of this work
was supported by the Deutsche Forschungsgemeinschaft (DFG Hu 46112-1 to
G.H.) and the National Science Foundation (S-005 to A.L. DeVries).