Fishes of the Southern Ocean surrounding Antarctica are dominated by species of the suborder Notothenoidei. For approximately 14MY, these highly successful fishes have evolved under stable thermal conditions that result in a body temperature of ca. 0 degrees C throughout their life histories. Evolution in this chronically cold environment has led to unusual physiological and biochemical characteristics. In some cases, these characteristics are essential to survival and normal biological function at cold body temperature (e.g., development of antifreeze glycoproteins, structural modification of enzymes, cold-stable microtubules, and cardiovascular adaptations). In other instances, mutations that probably would have been lethal in warmer, less oxygen-rich environments than the Southern Ocean have been retained in Antarctic fishes (e.g., loss of hemoglobin production and variable expression of myoglobin in one notothenioid family, the Channichthyidae). These unique animals offer opportunities for insight into evolutionary processes leading to physiological and biochemical characteristics that either arise from strong selective pressure or persist through relaxation of selective pressure. After briefly describing the Antarctic marine environment, I discuss several unique aspects of the physiology and biochemistry of Antarctic fishes, specifically emphasizing our laboratory's recent studies of an unusual pattern of myoglobin expression in the Channichthyid icefishes.