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‘Superheated ice’ found in Antarctic fishes

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‘Superheated ice’ found in Antarctic fishes

A new study from a multinational research team at the Universities of Auckland, Oregon and Illinois, working out of Scott Base and McMurdo Station, set out to understand how Antarctic fishes cope with ice build-up in their bodies.

The study describes a bizarre twist in the protective function of Antarctic fish antifreeze proteins, which comes at the cost of actually increasing their internal ice burden.

“What we have found is that antifreeze proteins not only stop ice from growing inside Antarctic fishes, but they also stop it from melting”, says Dr Clive Evans, a research scientist in the School of Biological Sciences at the University of Auckland.

“The ice inside the fish is actually ‘superheated’, that is it remains stable above its expected melting point, and this is a direct consequence of the binding of antifreeze proteins to the ice crystal surface.

“This is the first demonstration of the existence of ‘superheated ice’ inside living organisms, but it presents a significant problem for the fishes since the only known way for them to melt internal ice is through warming of the freezing seawater they inhabit.”

But using data going back more than a decade, the research team found seawater in Antarctica’s McMurdo Sound never reached temperatures that would melt all the ‘superheated ice’ in the resident fishes.

“Internal ice, protected by antifreeze proteins, seems a permanent burden for most fish in this area and is likely to prove lethal”, says Dr Evans.

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“What we have here is an evolutionary paradox. The adaptive evolution of fish antifreeze proteins has enabled Antarctic fishes to survive in freezing seawater by stopping internal ice from growing, but at they same time by inducing a “superheating” capacity these proteins have reduced the opportunity for melting the ice burden, thus increasing the risk of dying.”

This study may contribute more than just an improved understanding of the challenges Antarctic fishes face in their harsh environment. The long-term temperature record from McMurdo Sound will help scientists study the responses of a wide range of diverse Antarctic organisms as the waters warm in response to climate change.


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