This fish's blood is colourless because it has no red blood cells at all

Antarctic icefish are the only known vertebrates that survive without haemoglobin, the protein that makes blood red and carries oxygen in nearly every other animal. In the oxygen-rich, near-freezing Southern Ocean they get by on oxygen dissolved directly in blood plasma, antifreeze proteins that stop them freezing solid, and an oversized heart pumping thin, colourless blood through unusually wide vessels.

— Standard ichthyological accounts, Channichthyidae (crocodile icefish) — Family first described 1861; hemoglobin loss confirmed by later genetic study