The Icefish (or White-blooded fishes) are a family (Channichthyidae) of perciform fish found in the cold waters around Antarctica and southern South America.
Their blood is transparent because they have no hemoglobin and only defunct red blood cells. Their metabolism relies only on the oxygen dissolved in the liquid blood, which is believed to be absorbed directly through the skin from the water. This works because water can dissolve the most oxygen when it is coldest. Also, their muscles (except the heart muscle) lack the protein necessary for oxygen transport. These extraordinary properties seem to be an adaptation to the extreme cold of their habitat. (Note that water temperature can drop below 32Â°F (0 Â°C) (the freezing point of freshwater) in the Antarctic sea, but, on the other hand, stays rather constant.)
Channichthyidae are the only known vertebrates without hemoglobin. Icefish feed on krill, copepods, and other fish. There are fifteen known species of Icefish.