Some Pathways of Energy Metabolism Are Cold Adapted in Antarctic Fishes

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Abstract
Biochemical indices of metabolic cold adaptation were studied in muscular tissues of ecotypically similar Antarctic and Temperate Zone marine fishes. Pairwise comparisons were made between sluggish bottom-dwelling (polar: Notothenia gibberifrons; temperate: Myoxocephalus octodecimspinosus) and more active pelagic (polar: Trematomus newnesi; temperate: Tautoga onitis) species to ensure that results reflect differences in thermal habitats rather than life histories. Maximal activities of enzymes from central pathways of aerobic energy metabolism (citrate synthase, cytochrome oxidase) were 1.5-5-fold higher in oxidative muscles from polar species than from Temperate Zone counterparts when assayed at 1° C. Under similar conditions, enzyme markers for fatty acid oxidation (carnitine palmitoyltransferase, 3-hydroxyacyl-CoA dehydrogenase) were 1.3-27-fold higher in tissues from polar species, while those for both aerobic (hexokinase) and anaerobic (6-phosphofructokinase, pyruvate kinase, and lactate dehydrogenase) metabolism of carbohydrate were generally lower in tissues of polar than of Temperate Zone fishes. These data suggest significant metabolic cold adaptation of aerobic energy metabolism reliant upon fatty fuels inpolar species, but a lack of such adaptation in pathways of carbohydrate metabolism. In the Temperate Zone species, acute thermal sensitivities between 1° and 10° C of most catalysts from central pathways of aerobic energy metabolism were lower ( generally 2). If these patterns of thermal sensitivities are widespread, they may help explain selective expansion of aerobic metabolism to support activity at low body temperatures.