Bremer, Katharina (2007) Physiologie der Temperaturakklimatisation des Kabeljau (Gadus morhua). (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 78 pp.

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Abstract

Juvenile cod (Gadus morhua) of the southeastern North Sea, that describes its southernmost boundary of distribution, is exposed to drastic seasonal fluctuations in temperature. Typical water temperatures range between 15°C und 20°C in summer and drop to 3-6°C in winter. These extreme conditions limit the oxygen supply of the organism (aerobic capacity) until it is totally restricted by passing the critical temperature (Tc) (Frederich und Portner, 2000). At that point the metabolism becomes anaerobic. The aerobic capacity of an organism is defined as aerobic scope (AS). A diminishing AS will affect all higher functions (growth, reproduction and capacity of activity) of the fishes. For
North Sea cod the optimal temperature for maximum growth are 10°C (= maximal AS) (Portner et al., 2001). In the present study ASs were measured at 5°C and 16°C acclimated juvenile cod (350 g) and did not differ significantly. However, the AS of the l 6°C acclimated animals was more similar to the AS of cod from the 0resund (western Baltic Sea) acclimated to the optimum temperature of 10° C (Schurrnann and Steffensen (1997). Despite the slight (16°C acclimates animals) and relatively strong (5°C acclimated animals) deviations of the ASs of the present study compared to that from Schurrnann and Steffensen ( 1997), the fishes of both acclimation groups showed identical swimming performances to the fishes acclimated at the optimum temperature of 10°C. These adjustments could be explained by the enzyme activities of Citrate-Synthase (CS), Lactate Dehydrogenase (LDH) and L-3-HydroxacylCoA-Dehydrogenase (HADH) measured in white and in heart muscle. In white muscle there was full temperature compensation of both acclimation groups concerning all three enzymes. In heart muscle the l6°C acclimated fishes showed full compensation in their enzyme activity in comparison to the 5°C acclimated fishes. In the 5°C acclimated fishes just CS activity exhibited full compensation. When determining ecological relevant temperature ranges of fishes, duration of acclimation is an important factor. In this study saesonal temperature conditions were simulated with long phases of acclimation (66 days). The results of this work point to a relatively strong influence of temperatures <5° C on the North Sea cod, while temperatures about 16°C can be compensated very well by the animals. A negative temperature influence could be assumed for temperatures above 16°C.

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