Antarctic Fishes and the Physiological Significance of Blood Viscosity

Abstract

Viscosity increases with decreased temperature. The author argues that loss of hemoglobin is a “disaptation” or evolutionary loss of function which confers a competitive advantage in Antarctic waters because of decreased blood viscosity. Because the likelihood of developing turbulent flow is inversely related to viscosity, a minimum degree of blood viscosity is necessary. Also, pathologically high shear caused by insufficient viscosity will activate or damage the formed elements of blood such as leukocytes and platelets. The necessary viscosity in icefish is provided by antifreeze glycoproteins. Blood viscosity increases markedly with decreasing temperature. The viscosity of human blood at a normal hematocrit, 40%, at 0⁰ C was 16.7 cP at the high shear rate of 125/s in one study [1]. This is incompatible with life. Normal human blood viscosity at high shear rates is