Icefish of Antarctica

Bouvet Island is a tiny, desolate, and ice-covered hunk of volcanic rock in the Antarctic Ocean. Around it live sixteen species of fish that are unique among vertebrates: they live without hemoglobin.

As continental drift carried their island into colder waters, red blood cells became a liability, thickening their blood. The fish first dropped the proportion of red blood in their veins, then did away with it altogether. The cold water carries enough oxygen to keep them alive. Their gills have grown large and their skin is filled with capillaries that absorb oxygen directly from the water as does a frog’s.

The two genes for hemoglobin are no longer used. One has deteriorated to a garbled fragment and the other has vanished. In five species, the gene for myoglobin in the muscles has also vanished, leaving them with white instead of pink hearts. In all other vertebrate species, myoglobin binds oxygen in the muscles, close to where it is used.

Over 55 million years, other changes have adapted these fish to living in extra-cold water. But there’s no going back. If the water warms up again, they will go extinct—if we haven’t killed them off with overfishing, first.

–from Skeptical Inquirer magazine

2 Responses to “Icefish of Antarctica”

  1. jack Says:

    what kind of fish are they

  2. monado Says:

    They belong to the suborder Notothenioidei and it seems as if there might be more than sixteen species.

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