Nature’s Antifreeze

Life in the extreme environment of a polar ocean certainly is a survival challenge, but some Antarctic fish manage with ice water in their veins — literally.

In Antarctica’s coastal waters, a group of perch-like fish called icefish dominates. The water column in these frigid seas is filled with tiny ice crystals, and fish are constantly exposed to ice through their gills and skin. They even ingest ice crystals when they eat and drink.

All of this ice exposure would be enough to chill the fish down to the point of freezing to death — if not for a remarkable adaptation that stops the ice from doing damage.

Icefish don’t freeze thanks to glycoproteins in their blood that act as antifreeze. These specialized molecules bind to ice crystals that form in the fish’s body and stop the crystals from growing. Antifreeze glycoproteins work by covering the surface of ice crystals and blocking new water molecules from attaching to the crystal,
thus preventing the ice from expanding. Produced in the pancreas, the glycoproteins circulate in the fish’s blood, gut, and other bodily fluids, including the fluid surrounding the brain.

Scientists believe icefish developed these antifreeze proteins between 5 million and 14 million years ago, at a time when Antarctic waters cooled dramatically and fish that did not adapt died out. And what a successful adaptation it was! Icefish now account for 55 percent of the fish species found off Antarctica’s coast, enjoying a comfy living in an inhospitable environment.