Antifreeze: Why don’t Antarctic fish freeze to death?

It sounds like the superpower possessed by a lower level Marvel Comics superhero.

And while having antifreeze in your blood might be useful in those cases where one might say, be fighting crime in Moscow in December or uncovering crimes related to ice-cream trafficking, it’s an absolutely vital adaptation for fish living in the frigid waters of the Antarctic, where the water temperatures average minus 1.9 Celsius.

A video series called Reactions, produced by The American Chemical Society and PBS Digital Studios tackles the question of why fish in this area are not fish-cicles (Video below).

These special fish, called notothenioids, are a group that has evolved to sport a defense best described as a “biochemical antifreeze”. The fish have antifreeze proteins in their bodies that attach to the surface of ice crystals. These antifreeze glycoproteins, or AFGPs, are a more powerful defense against extreme cold than a Canada Goose parka fighting the cold winds on Toronto’s Front Street.

“This antifeeze action is so powerful it effectively creates a gap in the freezing point of the fish’s body fluid between where they should freeze and where they actually do,” says Alexa Billow, who wrote and narrated the video. They lower the fish’s internal freezing point by more than a degree Celsius, to as low as -2.7. Since the sea water can’t get much colder than it’s freezing point of -1.9, the fish literally can’t freeze.

This antifreeze super power is not exactly unique to the creatures of the Antarctic. Fish such as herring and scuplin and even insects such as certain beetles have the antifreeze adaptation, to varying degrees.

Billow notes that the type of antifreeze proteins are being explored for consumer applications such as preventing large ice crystals from forming on frozen ice cream and for improving the transport of live organs. Presumably, an array of applications lies between these oddly paired examples.

So does this clever adaptation mean notothenioids will be chilling out millions of years after mankind is gone? Maybe not, says a study published in the Journal of Experimental Biology by Jody M. Beers and Nishad Jayasundara, which concluded that warming conditions in the area may turn the feat into a mere parlour trick

“How notothenioids will fare in the rapidly changing Southern Ocean remains an open question,” the authors says. “It is interesting to speculate what will become of the biochemical adaptations to low, near-freezing temperatures, such as the AFGPs, which may no longer be needed in a warmer ocean. Indeed, production and maintenance of these proteins are likely to be energetically costly and may be selected against over time. Reduction and loss of AFGPs has already been documented in notothenioids that have migrated to warmer latitudes from endemic waters with seemingly no negative repercussions.

Below: How Not to Freeze a Fish