Antarctic Fish Have Ice in Their Veins

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.)