The Antarctic Ocean-dwelling ocellated icefish is an anomaly in the natural world, as the only vertebrate with transparent blood.
Icefish have "no hemoglobin that carries oxygen into the blood," said Naoaki Kawahara, a fish keeper at Tokyo Sea Life Park, the only aquarium in the world to exhibit the unusual creature.
Hemoglobin is the protein that normally gives blood its red color, but its absence in the icefish also means the species has white muscles, liver and even gills, which are normally bright red.