Why do Antarctic icefishes appear to have bloodless bodies?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Bluefin tuna swimming underwater in a group, with silvery bodies and streamlined shapes, near Japan. — perciform Bluefin tuna (*Thunnus thynnus orientalis*) in the waters near Japan.

Antarctic icefishes, specifically members of the family Channichthyidae (order Perciformes), appear to have bloodless bodies because they lack hemoglobin and red blood cells, which typically give blood its red color.1

Rather than relying on hemoglobin to transport oxygen, these fish have adapted to the oxygen-rich waters of the Southern Ocean by evolving larger hearts and expanded gill blood vessels. These physiological features allow them to circulate a significantly greater volume of blood, which is sufficient to extract the necessary oxygen directly from the water despite the absence of oxygen-carrying pigments.1