Evol Ecol Res 6: 1123-1144 (2004) Full PDF if your library subscribes.
Colonization of the freshwater environment by a marine invader: how to cope with warm summer temperatures?
Franz Hölker,* Sven Volkmann, Christian Wolter, Peter L.M. van Dijk and Iris Hardewig
Leibniz-Institute of Freshwater Ecology and Inland Fisheries, PO Box 850119, 12561 Berlin, Germany
Author to whom all correspondence should be addressed.
The burbot Lota lota (L.) is the only member of the cold-stenothermal marine family Gadidae that invaded freshwater. To evaluate the evolutionary strategy allowing the invasion of freshwater habitats with high temperature amplitudes, we determined seasonal variations of the energy budget for juvenile burbot from the River Oder, Germany. Food consumption during summer was not sufficient to meet the animal’s energetic requirements. During winter and spring, energy uptake surpassed the metabolic energy flux and left surplus energy for growth. Burbot growth is maintained throughout the year by two mechanisms: (1) growth that is reflected predominantly in length throughout the summer, when energy-rich liver tissue must be metabolized to provide energy, and (2) a synthesis of liver reserves during winter, when energy uptake exceeds energy dissipation. In contrast to most freshwater fish, which reduce growth rates during the winter months, the evolutionary burden of being cold-adapted, inherited from its marine ancestors, enables L. lota to maintain somatic growth throughout the year.
Keywords: bioenergetics, cold-stenotherm, Gadidae, growth, Lota lota, temperature tolerance.
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