Every animal living in the Antarctic faces a unique challenge: how to survive in sub-zero weather.
A research team recently discovered that several species of Antarctic notothenioid fish manage to live in the cold waters by producing proteins similar to antifreeze, which keep pieces of ice inside the fish from getting larger. However, these same proteins have an unintended consequence which may be harmful to the fish: they also keep the ice from melting.
The team found that when the antifreeze proteins attach to a piece of ice, either inside of the fish or in a larger solution of water, the protein keeps the ice from melting even when the ice is heated beyond its normal melting point. Ice that remains solid beyond its normal melting point is called "superheated" ice. This may be the first-ever discovered case of superheated ice found in nature, according to the researchers.
The study is a collaboration between researchers from the University of Oregon and the University of Illinois. Paul Cziko and the rest of the team spent most of the past two years studying Antarctic ice fish, such as the Antarctic toothfish, to learn everything possible about how the fish survive in freezing waters. Not all fish that live in Antarctica have this feature; it is mostly studied in Notothenioid fish.
Right now the team is trying to learn how having tiny pieces of ice that won't melt inside of them affects the fish. Professor Chi-Hing "Christina" Cheng, one of the team's leaders, said that the ice may be harming the fish in some way.
Cziko said that the pieces of ice might be similar to blood clots in humans.
"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 said.
Cziko said that the team's research is not intended to have any practical application at this point. The team is just learning what they can about evolution. The Antarctic fish are an interesting case of an evolutionary advantage that comes coupled with a downside: the protein keeps ice inside the fish from freezing, preventing it from growing inside of the fish, but it also prevents the ice from melting, meaning there might be a harmful buildup of ice shards inside the fish.
The antifreeze protein first developed approximately 20 million years ago, Cheng's team discovered last year. The fish developed the ability to survive sometime after the Antarctic froze over. The team analyzed the Antarctic toothfish's DNA and compared it to a genetically similar fish that does not live in the Antarctic, Eleginops maclovinus, to glean what it could about the fish's adaptation.
