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Why Don't Antarctic Fish Freeze?
An iceberg drifts in the Southern Ocean, where water temperatures would be colder than the freezing point of fish blood, were it not for special antifreeze proteins.
Credit: Lieutenant Philip Hall, NOAA Corps

The frigid waters of the Antarctic Ocean should be cold enough to freeze fish blood. A natural antifreeze however, keeps the fish blood flowing.

The Antarctic Ocean's freezing temperatures of 28.8 degrees Fahrenheit (minus 1.8 degrees Celsius) are lower than the freezing point of fish blood, which is about 30.4 degrees F (minus 0.9 degrees C), which would seem to suggest that all those fish should be frozen in their tracks.

How fish are able to keep moving at these temperatures puzzled researchers for more than 50 years, until special frost protection proteins were found in the blood of the cold-water fish. These so-called antifreeze proteins work better than any household antifreeze at keeping the fish from becoming fish-cicles. How they work, however, has been unclear.

To get to the bottom of this chemical question, scientists studied the antifreeze proteins of the Antarctic toothfish (Dissostichus mawsoni), which one of researchers caught while on an Antarctic expedition.

Scientists used a special technique to record the motion of water molecules mixed with antifreeze proteins from the fish. In the presence of these antifreeze proteins, the water molecules danced a more ordered dance than they otherwise would have. In other words, the antifreeze proteins disturbed the water molecules in such a way that they could not bond together and form ice crystals.

"The disco dance becomes a minuet," said study team member Martina Havenith of the Ruhr University Bochum in Germany.

The study was detailed in the Aug. 16 edition of the Journal of the American Chemical Society.

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