It is quite interesting to note that icefish do not have any hemoglobin or red blood cells, meaning they have white or clear blood. They are the only vertebrates to lack both of these. Early research suggested that crocodile icefish blood lacks red blood cells and hemoglobin as they had already absorbed enough oxygen from the extremely low-temperature but oxygen-rich waters of their surroundings. It was thought that this adaptation made their blood thinner which helped the blood in their bodies to circulate faster. This also aided in adapting to an extreme environment. However, new developments in science have revealed that the lack of hemoglobin and red blood cells might be accidental, as the absence of the protein hemoglobin along with red blood cells has reduced the oxygen-carrying capability of their blood.