Certain Antarctic fish species can create proteins that allow their bodies to remain unfrozen in the sub-freezing temperatures around Antarctica's Southern Ocean. As amazing as this process is inside the anatomy of these fish, there is a downside to it. Scientists studying these fish recently published their findings in the Proceedings of the National Academy of Sciences detailing how the 'anti-freeze' proteins that keep the fish from freezing don't melt, even when in warmer water. 

Paul Cziko is a doctoral student at the University of Oregon and led the research examining the fishes' special proteins. "We discovered what appears to be an undesirable consequence of the evolution of antifreeze proteins in Antarctic notothenioid fishes," explained Cziko. "What we found is that the antifreeze proteins also stop internal ice crystals from melting. That is, they are anti-melt proteins as well." 

According to the University of Illinois, five "families" of these notothenioid fish live in the Southern Ocean, and this ability to adapt to the sub-freezing waters surrounding Antarctica is so rare among fish, that the notothenioid species make up 90% of the fish "biomass" in that region.

While the special properties of these fish and their proteins have been known since the 1960's, researchers in this most recent study set out to understand if the anti-freeze protein crystals would melt when the fish they reside in encounter warmer temperatures. 

"Our discovery may be the first example of ice superheating in nature," University of Illinois researcher Chi-Hing Cheng said. Superheating refers to when a crystal (like ice), for whatever reason, doesn't melt at its usual melting point. 

Researchers also suspect that since these crystals don't melt inside the fish and they are accumulated over its lifespan, they could cause certain health problems. However, at this point, no harmful effects have been identified. 

"This is just one more piece in the puzzle of how notothenioids came to dominate the ocean around Antarctica," Cziko explained. "It 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."