"Chaenocephalus aceratus" by Ambiederman / CC BY-SA 4.0

How the Icefish Got Its Transparent Blood and See-Through Skull

Mar 1, 2019

By JoAnna Klein

The Southern Ocean around Antarctica was once warmer. Then about 30 million years ago, the temperature dropped. Few fish could survive temperatures that were just above seawater’s freezing point, and they either migrated to warmer waters or went extinct.

One bottom-dweller held on. Through the power of natural selection, its descendants developed traits that let them survive these unlikely conditions. Today, the Antarctic blackfin icefish, or Chaenocephalus aceratus, thrives in these frigid waters with no scales, blood as clear as water and bones so thin, you can see its brain through its skull.

How this creature — no longer a bottom-dweller — can live in such a hostile environment has long fascinated scientists, who have mapped its genome and continued exploring its unusual traits. In a paper published Monday in Nature Ecology and Evolution, a team of scientists compared the genome of the Antarctic blackfin icefish to those of its close relatives. They found that, across these genomic maps, and tens of millions of years of evolution, gene families had shrunken or expanded, giving rise to some of the icefish’s most unusual features. In addition to revealing how the icefish managed to adapt to extreme Antarctic conditions, the team’s findings provide a new way to look at the genetics behind human diseases such as anemia and osteoporosis.

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