In addition to having antifreeze proteins, icefish do not produce red blood cells or hemoglobin. As a result, their blood is less viscous and can flow easily even at very cold temperatures. However, having no hemoglobin greatly reduces the amount of oxygen that a given volume of blood can carry.

Did icefish ancestors have hemoglobin?

Among the hundreds of red-blooded Notothenioid species, only the icefishes lack hemoglobin.

Does the icefish have blood?

Blood As White As Snow

All vertebrates have red blood cells—that is, except for a small family of fish from the notothenoid family known collectively as “icefish.” These Antarctic-dwelling fish have translucent blood, white hearts, and have somehow adapted to live without red blood cells or hemoglobin.