Weird Gramma
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Mackerel icefish, a clear-blooded cod-icefish.
Photo by Pablo Ricardo Reyes Lobalo-Tello, Universidad Austral de Chile.
Patagonian toothfish, also called Chilean sea bass.
Photo by Monterey Bay Aquarium Seafood Watch.

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Weird Gramma here with “WeirdFins,” all about strange stuff in the sea, and brought to you by the National Oceanic and Atmospheric Administration. Did you know there are fish whose bodies contain antifreeze, like the stuff that keeps a car’s cooling water from freezing? Yep, it’s true! Many kinds of cod-icefishes, which live near the South Pole, make a kind of antifreeze so that the icy water doesn’t kill them. Here’s how it works.

Water turns into ice at what’s called the freezing point, and if you’re in water at that point for more than a few minutes, ice crystals will begin to form in your flesh and innards, and then destroy your body cells. This happens to most fish and other animals, too. But the cod-icefish’s antifreeze particles attach to ice crystals and make it hard for the crystals to grow.

Now, this is a pretty nifty trick, and some crafty humans have figured out that this cod-icefish antifreeze could be useful to us, too. So the stuff is now being used to help improve the quality of frozen foods, and protect blood cells, transplant organs, and other tissues that are frozen for later medical use.

Here’s another weird thing about one group of these critters: They’re the only known vertebrates—animals with backbones—that lack hemoglobin. Hemoglobin is that stuff in blood that carries oxygen to all the cells. But because icy Antarctic waters are loaded with so much oxygen, these cod-icefishes can absorb all the oxygen they need directly through their skin. And with no hemoglobin, which is what makes blood bright red, these fish have blood that’s completely transparent! The clear-blooded icefishes aren’t fished for food, but a cousin, the Chilean sea bass, is popular. . . .and delicious!

You can see pictures of cod-icefishes on the National Marine Fisheries Service WeirdFins link at

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