 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 according to a new study published in the journal Proceedings of the National Academy of Sciences, researchers have revealed that these proteins may not be as helpful as they were once thought to be. That's right, the same antifreeze proteins that latch onto ice crystals and prevent them from growing also inhibit them from melting. To investigate if ice inside high-latitude Antarctic notothenioid fishes could melt seasonally, we measured its melting point and obtained a decadal temperature record from a shallow benthic fish habitat in McMurdo Sound, Antarctica. The research group found that the ice crystals didn't melt at their expected melting point of about 30 degrees Fahrenheit, but instead remained intact. Rather than acting like a salt and lowering the freezing point, the notothenioids' antifreeze proteins bind themselves to the ice crystals in their bodies and alter the surface of the crystals so that they have a hard time growing any larger. Field experiments confirmed that superheated ice occurs naturally inside wild fishes. Whether and how fishes eliminate internal ice is unknown; one hypothesis is that it melts during summer warming episodes. "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.
– How do the fish that thrive in the waters around Antarctica prevent their blood from turning to ice? Turns out at least some of them don't. Scientists have long known that the group of fish species known as notothenioids have an antifreeze protein in their blood that prevents them from being frozen to death, but new research has revealed that the same protein keeps ice crystals in their veins, apparently permanently, UPI reports. The crystals melted at a few degrees above freezing, but the fish may spend their whole lives without encountering temperatures that warm, according to research published in the Proceedings of the National Academy of Sciences. The antifreeze proteins that prevented the blood from completely freezing also bound itself to the ice crystals, keeping them from getting smaller, the scientists say. Lead researcher Paul Cziko tells the Christian Science Monitor that it's not clear whether the fish have evolved some way of dealing with the ice crystals in their bodies, or if the ice ends up killing them in the long term. "This shows that with every good evolutionary innovation, some potentially bad or unintended consequences come along with that," he says. "Evolution is a stepwise process. You take two steps forward, and take one step back." (Researchers recently solved the decades-old mystery of a quacking noise detected in Antarctic waters.)