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Antarctic fish have antifreeze in their veins

"We discovered what appears to be an undesirable consequence of the evolution of antifreeze proteins in Antarctic notothenioid fishes," said Paul Cziko.

By Brooks Hays
A notothenioid fish species which can withstand the cold of the Antarctic thanks to antifreeze proteins in their blood. (University of Illinois)
A notothenioid fish species which can withstand the cold of the Antarctic thanks to antifreeze proteins in their blood. (University of Illinois)

EUGENE, Ore., Sept. 23 (UPI) -- Fish species that make their home in the frigid waters of Antarctica have developed special antifreeze proteins that keep their blood from icing over. But evolution is a strange game in which seemingly every adaptive trait comes with a trade-off, and for the fish of Antarctica that trade-off is quite the paradox.

For the benefit of avoiding frozen blood, Antarctic notothenioid fish species must tolerate ice in their veins. That's right, the same antifreeze proteins that latch onto ice crystals and prevent them from growing also inhibit them from melting.

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A team of marine biologists discovered the odd trade-off while studying the coping mechanisms of notothenioid species living in supremely cold conditions. They discovered the antifreeze proteins' anti-melting properties after raising water temperatures slightly above the freezing point and still finding some ice in the blood of the fish specimens.

"We discovered what appears to be an undesirable consequence of the evolution of antifreeze proteins in Antarctic notothenioid fishes," study author Paul Cziko, a doctoral student the University of Oregon's Institute of Ecology and Evolution, said in a press release.

If water temperature rises more than two or three degrees above the freezing point, these ice crystals are likely to melt. But Cziko and his colleagues at the University of Illinois found that ocean temperatures in the Antarctic rarely ever rose high enough to help clean the species icy veins. That means these fish carry ice crystals around with them for most of their lives -- a risky proposition that could help them stay cool under pressure but could also cause a life-threatening traffic jam inside small capillaries.

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"Since much of the ice accumulates in the fishes' spleens, we think there may be a mechanism to clear the ice from the circulation," Cziko added. "This is just one more piece in the puzzle of how notothenioids came to dominate the ocean around Antarctica."

The study was published in the Proceedings of the National Academy of Sciences on Monday.

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