Natural 'Antifreeze' Found in Antarctic Fish Also Prevents Melting

Researchers have determined that the "antifreeze" proteins that are naturally produced in the bodies of many Antarctic fish also suffer from an unexpected side effect. According to a new study, these same anti-freezing properties make it harder for these fish to thaw in warm water.

Paul Cziko, who led this study of Antarctic fish with the University of Illinois, calls the anti-melting side of the protein "an undesirable consequence of evolution."

"What we found is that the antifreeze proteins also stop internal ice crystals from melting... in Antarctic notothenioid fishes," he explained in a recent statement. "That is, they are anti-melt proteins as well."

According to the study, which was recently published in the journal Proceedings of the National Academy of Sciences, five families of notothenioid fishes inhabit the Southern Ocean, the frigid sea that encircles Antarctica. The fish are incredibly prevalent there, making up 90 percent of the entire fish biomass in the region simply because their incredible freeze resistance allows them to live where most fish would be turned into popsicles in a matter of minutes.

According to earlier studies, the specialized proteins in these fish bind ice crystals in the blood, preventing them from locking together and freezing the fish. But as a consequence, these same crystals stick around even when the fish enter warmer waters - causing them to exist beyond their natural melting point.

"Our discovery may be the first example of ice superheating in nature," added co-author Chi-Hing Cheng.

After tracking the fish and recording temperature for 11 years, researchers say, not once were they found to be completely rid of the ice in their veins, even in comfortably warm water. Yet somehow, despite constantly accumulating ice every cold season, these fish live on.

"Since much of the ice accumulates in the fishes' spleens, we think there may be a mechanism to clear the ice from the circulation," explained Cziko. "[This study] also tells us something about evolution. That is, adaptation is a story of trade-offs and compromise. Every good evolutionary innovation probably comes with some bad, unintended effects."