Antarctic icefish-Only known vertebrate in the world that doesn’t have red blood cells

Antarctic icefish belong to the Channichthyidae family and are found in the freezing Southern Ocean around Antarctica.

They are the only known vertebrates that lose haemoglobin as adults, resulting in colourless blood with no red blood cells.

In some species, myoglobin, the oxygen-storing protein in muscles, is also absent.

According to a study published in the Journal of Experimental Biology (2006), the loss of haemoglobin occurred due to a genetic mutation.

Without haemoglobin, the blood of icefish carries less than 10% of the oxygen transported by the blood of closely related red-blooded fish.

To compensate for this, icefish have evolved several adaptations:

• A heart four to five times larger (relative to body size) than that of related fish.
• Up to four times more blood volume.
• Wider blood vessels to circulate oxygen-poor blood more efficiently.

These adaptations are energy-intensive, requiring the fish to use about twice as much energy to pump blood.

Icefish survive because the Southern Ocean’s extremely cold water contains high levels of dissolved oxygen.

They can absorb oxygen directly through their blood plasma and scaleless skin, reducing their dependence on haemoglobin for oxygen transport.

The unique physiology of Antarctic icefish makes them an important model for studying evolution, adaptation to extreme environments, and cardiovascular biology.

Source: ToI

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