The changing decrease in temperature of the southern ocean in geological history has lead to the extensive radiation of a group of fish, the suborder Notothenioidei. These fish have evolved an adaptive characteristic, antifreeze proteins, to help them survive the —1.8 •C freezing waters of the southern ocean. These antifreeze proteins are large repeating units of glycotripeptide structures with a linked disaccharide unit that adsorbs to an ice crystal lattice and lowers the freezing point Of the water so as to prevent the ice from growing inside the animals tissues, which is potentially lethal. It is the presence of these antifreeze proteins that allow these fish to dominate the fish fauna in the freezing waters of the southern ocean today. The changing decrease in temperature of the southern ocean in geological history has lead to the extensive radiation of a group of fish, the suborder Notothenioidei. These fish have evolved an adaptive characteristic, antifreeze proteins, to help them survive the —1.8 •C freezing waters of the southern ocean. These antifreeze proteins are large repeating units of glycotripeptide structures with a linked disaccharide unit that adsorbs to an ice crystal lattice and lowers the freezing point Of the water so as to prevent the ice from growing inside the animals tissues, which is potentially lethal. It is the presence of these antifreeze proteins that allow these fish to dominate the fish fauna in the freezing waters of the southern ocean today.