Antarctic fish that survive in harsh temperatures thanks to special antifreeze proteins have presented an "evolutionary paradox" to scientists.

A team of researchers from the U.S. and New Zealand has discovered that these unique proteins not only keep ice from growing inside the fish's body but also prevent the ice from melting, and they detailed the findings in a study published Monday, the New York Times reported.

"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," Dr. Clive Evans, a research scientist in the School of Biological Sciences at the University of Auckland, said in a statement.

"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."

Lead researcher Paul A. Cziko spent several seasons in Antarctica studying the fish, which weren't particularly choosy when it came to bait.

 "They bite pretty much anything," Cziko told the Times.

Collecting the Antarctic fish meant diving beneath the ice to capture them as well as drilling holes 10 inches wide in ice sheets that could be as much as 20 feet thick.

While the proteins protect the fish in below freezing temperatures, they also allow ice to build up dangerously inside the creature.

"Internal ice, protected by antifreeze proteins, seems a permanent burden for most fish in this area and is likely to prove lethal," Evans said. "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 the same time by inducing a 'superheating' capacity these proteins have reduced the opportunity for melting the ice burden, thus increasing the risk of dying."

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