USE AN ANTIFREEZE
Stopping ice crystals forming is the key
The crocodile icefish, which lives in the freezing waters around the South Pole, has a natural antifreeze in its blood. Saltwater freezes at a lower temperature than freshwater, and the icefish live in seas as cold as -2 degrees
Celsius – conditions that would kill most fish species. As with the wood frog, it’s a protein that protects the crocodile icefish. Known as an ice-structuring protein, it binds to ice crystals as they form in the fish’s blood and prevents them from growing any larger while also inhibiting the growth of new ones. It can do this because ice crystals have flat surfaces it can stick to – something not usually found in blood cells.
Icefish blood also has fewer red blood cells than most other species. This means its blood is less viscous and able to keep flowing in extremely cold temperatures. The crocodile icefish has so little haemoglobin that its blood is yellow. These fish are able to survive because their Southern Ocean home is high in dissolved oxygen, the solubility of which is increased at low temperatures – enough to be carried in blood plasma. The icefish is not the only living thing to fight the cold in this way. The winter flounder, which lives in the cold waters at the opposite end of the planet, also uses the same technique.
Winter rye grass also uses similar icestructuring proteins in its leaves and stems to survive low temperatures and keep growing through the winter. The proteins also occur in at least 23 species of flowering plants, as well as some fungi and bacteria. In 2002 the American Food and Drug Administration (FDA) received an application to use ice-structuring proteins in ice cream, which it approved. These proteins are the same as in fish, but are produced using genetically modified yeast. They prevent ice crystals forming in frozen desserts, spoiling the texture, in the same way they do in icefish blood.