The Oxidative Metabolism of Antarctic Fish: Some Peculiar Aspects of Cold Adaptation

Environmental factors are key determinants in the process of adaptation and evolution of living organisms. In this respect, analysis of biological systems from Antarctic fish may provide valuable insights on the molecular and cellular strategies which have been adopted in response to the very low environmental temperature which characterizes Antarctica. Hence, the temperature of the Antarctic Ocean varies from −1.86 °C at high latitudes to +5 °C towards the Antarctic Convergence. Moreover, seasonal variations in temperature are less than 0.2 °C close to the permanent ice shelf [1] and only 2.5 °C in the northern Antarctic [2]. Very likely these conditions have existed relatively unchanged for several million years [3]. Antarctic fish have therefore been forced to become highly specialized to cold conditions [4]. This extreme specialization is outlined by the fact that a water temperature of −1.8 °C, near the freezing point of sea water, is a condition which would be lethal for virtually all other fish. Among antarctic fishes the strong challenge of this extreme environmental condition has been overcome by a number of physiological and biochemical adaptation mechanisms, the most striking of which is the synthesis of freezing-point depressing molecules (antifreeze molecules), either peptides or glycopeptides, which protect the organism from ice crystal formation in a noncolligative way [5]. In addition, hematocrit of the blood is either substantially reduced or erythrocytes and hemoglobin are absent as in Channichthyidae [6, 7, 8].