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Why do some fish have colourless blood?

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What they lack in colour, they make up for with a big heart…

Asked by: Lorely Maskell, Buckinghamshire

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Antarctic icefish have colourless blood with no red blood cells and no haemoglobin, the oxygen-carrying pigment. This probably comes down to a genetic mutation, and means their blood carries 90 per cent less oxygen than red blood. They survive partly because frigid Antarctic waters are oxygen-rich. Icefish also have enormous hearts that pump huge volumes of blood around their bodies, making sure they get enough oxygen. Antifreeze in their blood stops them from freezing (the salty Southern Ocean gets down to -2°C) but as they are so well-adapted to the cold, their future in a warming world remains uncertain.


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Authors

Dr Helen Scales is a marine biologist, broadcaster and science writer. She is the author of Spirals in Time and The Brilliant Abyss.

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