The impossible claim

This fish has no red blood cells and no hemoglobin — its blood is nearly clear. It’s the only vertebrate on Earth like this.

The verified facts

The Antarctic icefish (Chaenocephalus aceratus and relatives, family Channichthyidae) are the only vertebrates that lack hemoglobin and red blood cells. Their blood is nearly transparent — essentially clear plasma. In −1.8 °C Antarctic water, oxygen dissolves so well that the icefish survives on oxygen simply diffusing into its blood plasma (~10% the capacity of red-blooded fish).

  • Norwegian biologist Ditlef Rustad noted ‘Blod farveløst’ (colorless blood) in his 1927 notebook; Johan T. Ruud proved it in Nature (1954)
  • Compensations: a markedly enlarged heart, high blood volume, and wide vessels pump plasma fast enough to deliver oxygen
  • Antifreeze glycoproteins circulate in their blood, binding ice crystals so they can’t grow — the fish never freezes solid
  • Hemoglobin genes were deleted outright — genomic ‘fossils’ of globin genes remain in their DNA (Nature Ecology & Evolution 2019)

Watch

🎬 See the Short on YouTube — The Fish With Clear Blood

Sources

  • Ruud, J. T. (1954). Vertebrates without erythrocytes and blood pigment: a new family of fish from Antarctica. Nature.
  • Rustad, D. (1927, publ. 1930s). First report of colorless blood in Chaenocephalus aceratus (field observation).
  • Near, T. J. et al. (2019). Genomic basis of hemoglobin loss in Antarctic icefish. Nature Ecology & Evolution.
  • Sidell, B. D. & O’Brien, K. M. (2006). When bad things happen to good fish: the loss of hemoglobin and myoglobin expression in Antarctic icefishes. Journal of Experimental Biology.

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