Their blood contains substances that act as antifreeze.
Fish are cold-blooded creatures, which means that their body temperature matches the temperature of the surrounding environment. In particular, in McMurdo Sound, located near the South Pole, water temperatures sometimes drop below -2 °C. However, polar fish species do not freeze because they produce glycoproteins—special proteins that were discovered in their blood in the mid-20th century.
These glycoproteins are very effective cryoprotectants: they slow down the freezing process of liquids 200–300 times better than regular salt, which is added to water to prevent freezing. It was initially thought that glycoproteins bind to one of the facets of ice crystals forming in cells and slow their growth.
However, research has shown that they act on water molecules at a distance. In the presence of glycoproteins, the movement of molecules in the aqueous solution becomes less chaotic, and they are less likely to bond with each other into a crystalline lattice. In terms of effectiveness, glycoproteins surpass traditional antifreezes.
