U.S. scientists headed by Dr Chi-Hing Christina Cheng of the University of Illinois at Urbana–Champaign have discovered that the so-called ‘antifreeze’ proteins that bind to crystals of ice inside Antarctic notothenioid fishes to keep their bodies from freezing also prevent the ice from melting when temperatures warm.
The Emerald rockcod (Trematomus bernacchii) is a common notothenioid species. Image credit: Zureks / CC BY-SA 3.0.
Antarctic fishes of the suborder Notothenioidei live at seawater temperatures between minus 1.9 and plus 4 degrees Celsius. Temperatures below the freezing point of pure water (0 degrees Celsius) are possible due to the dissolved salts.
In the 1960s, ichthyologists discovered that these fishes rely on the presence of specific ‘antifreeze’ proteins in their blood and other body fluids to survive in such extreme environment.
In a new study, Dr Cheng and her colleagues investigated whether the antifreeze protein-bound ice crystals inside notothenioid fishes would melt as expected when temperatures warmed.
When they warmed the fishes to temperatures above the expected melting point, some internal ice crystals failed to melt. Ice that doesn’t melt at its normal melting point is referred to as ‘superheated.’
The team also found ice crystals in wild notothenioid fishes swimming in relatively warmer Antarctic summer waters, at temperatures where they would be expected to be free of ice.
By testing the antifreeze proteins in the lab, the scientists found that these proteins also were responsible for preventing the internal ice crystals from melting.
“Our discovery may be the first example of ice superheating in nature,” said Dr Cheng, who is the senior author of the paper published in the Proceedings of the National Academy of Sciences.
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Paul A. Cziko et al. Antifreeze protein-induced superheating of ice inside Antarctic notothenioid fishes inhibits melting during summer warming. PNAS, published online September 22, 2014; doi: 10.1073/pnas.1410256111
