For researchers trying to understand the physiology of blood and vascular systems, certain animals hold a special allure as a probe of their theories. Antarctic icefishes are such an animal.
All other animals with backbones have red blood. This color is due to the iron containing protein hemoglobin. Hemoglobin performs the vital function of ferrying oxygen through the bloodstream from respiratory organs like lungs or gills to all parts of the body. Most of the blood’s hemoglobin is packed into red blood cells, the most abundant cell type in blood.
In 1928 biologist Ditlef Rustad caught an unusual, eerily pale fish in waters near Antarctica. Rustad discovered, to his astonishment, that the fishes’ blood was transparent, lacking mature red blood cells and hemoglobin. Such Antarctic icefishes are now known to be abundant in the waters surrounding Antarctica; occupying the subfreezing waters of the coldest environment on Earth. All sixteen species of icefishes lack hemoglobin.
How could icefish survive without hemoglobin?
When water is very cold, its ability to carry oxygen is enhanced, and hemoglobin’s effectiveness is reduced. Oxygen diffuses through the icefishes’ enlarged gills, and maybe through its smooth skin, directly into its blood plasma, where it is carried through the body. Icefish blood can only carry about ten percent as much oxygen as in other fish, but this is good enough for the sluggish icefish to survive.
Why do icefish lack hemoglobin? We actually don’t know. Some think it was a helpful adaptation to the cold. Extreme cold causes red blood to thicken, making it more difficult to circulate. Others think it was, overall, a harmful mutation, but that the icefish evolved in other ways to cope.
Reviewer: Thomas Desvignes, the University of Oregon
Read more
- How red is "blood red" really?
- The evolution of diving in mammals and myoglobin
- How does the body make blood?
Sources
- Scientific American - How the Antarctic icefish lost its red blood cells but survived anyway
- Quanta Magazine - Icefish study adds another color to the story of blood
- The New York Times - How the icefish got its transparent blood and see-through skull
- Northeastern University College of Science - Icefish have antifreeze in their blood, anemia, and osteoperosis. And they feel just fine
- Nature Ecology & Evolution - Antarctic blackfin icefish genome reveals adaptations to extreme environments
- Journal of Experimental Biology - When bad things happen to good fish: the loss of hemoglobin and myoglobin expression in Antarctic icefishes
For researchers trying to understand the physiology of blood and vascular systems, certain animals hold a special allure as a probe of their theories. Antarctic icefishes are such an animal. All other animals with backbones have red blood. This color is due to the iron containing protein hemoglobin. Hemoglobin performs the vital function of ferrying oxygen through the bloodstream from respiratory organs like lungs or gills to all parts of the body. Most of the blood’s hemoglobin is packed into red blood cells, the most abundant cell type in blood.
In 1928 biologist Ditlef Rustad caught an unusual, eerily pale fish in waters near Antarctica. Rustad discovered, to his astonishment, that the fishes’ blood was transparent, lacking mature red blood cells and hemoglobin. Such Antarctic icefishes are now known to be abundant in the waters surrounding Antarctica; occupying the subfreezing waters of the coldest environment on Earth. All sixteen species of icefishes lack hemoglobin.
How could icefish survive without hemoglobin? When water is very cold, its ability to carry oxygen is enhanced, and hemoglobin’s effectiveness is reduced. Oxygen diffuses through the icefishes’ enlarged gills, and maybe through its smooth skin, directly into its blood plasma, where it is carried through the body. Icefish blood can only carry about ten percent as much oxygen as in other fish, but this is good enough for the sluggish icefish to survive.
Why do icefish lack hemoglobin? We actually don’t know. Some think it was a helpful adaptation to the cold. Extreme cold causes red blood to thicken, making it more difficult to circulate. Others think it was, overall, a harmful mutation, but that the icefish evolved in other ways to cope.