Wednesday, May 02, 2007

Icefish With Anti-Freeze

The Antarctic blizzard rages and howls, blanketing the landscape in lifeless snow. Offshore, below the ice, in the dark of the bitterly cold water, a fish moves slowly across the seabed. The icefish is long and scaleless, with a snout like a duck's bill and strange white gills that give it its name.
Life in the freezing waters around Antarctica demands very unusual adaptations. Only about 120 species of fish manage to survive there, out of a world total of around 20,000 fish species. Of the 17 species of icefish known to man, most are between 450 and 600 mm (1.5 and 2 ft) long. and are bottom-dwellers that prey on smaller fish and crustaceans.
The icefish is unique. It is the only vertebrate in the world that has no haemoglobin, the red oxygen-carrying pigment that gives our blood its colour. Although the amount of oxygen it can dissolve in its blood plasma is very small, the absorption of oxygen by its tissues is unusually efficient. And since the icefish has no red blood cells, its translucent, yellowish blood is thin, and is easily pumped round the body. Its heart is large, as are its blood vessels, so the icefish maintains good circulation, despite expending less energy than a red-blooded fish.
Scientists think that Antarctic fish, including the icefish, have another important weapon against the freezing waters - natural antifreeze. Chemicals called glycopeptides that circulate in their blood seem to prevent the formation of ice crystals in their body fluids.

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