Icefish are a unique group of fish found in Antarctic and sub-Antarctic waters of the Southern Ocean, also called the Antarctic Ocean. The first icefish, later named as the blackfin icefish, Chaenocephalus aceratus, was discovered in 1927 by a Norwegian zoologist, Ditlef Rustad, in Antarctic waters. It belonged to the Channichthyidae family of fishes and is also called as crocodile icefish or white-blooded fish because it resembles a little crocodile and has transparent haemoglobin-free blood. As they lack red blood cells—considered to be the main carrier of Oxygen in the blood—scientists are of the opinion that certain body adaptations like larger hearts, wide blood vessels, large gills, and having no scales on body help them circulate a greater volume of blood and extract sufficient oxygen from the oxygen-rich waters of the Southern Ocean.
Moreover, the absence of haemoglobin makes their blood less viscous, allowing it to flow more easily even in extremely cold temperatures.
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The National Geographic Society recognised the oceanic ring of water around Antarctica as the world’s fifth ocean, known as the Southern Ocean, on June 8, the World Ocean Day.
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Some Salient Features
Icefish have greyish, black or brown bodies with wide pectoral fins and two dorsal fins that are supported by long flexible spines. They grow to a maximum length of about 30 centimetres. Their larvae are 17 mm long when they hatch, and grow by about 2 mm a week. The larval stage lasts for up to 18 months. The eggs of the icefish hatch in about six months’ time. Icefish become sexually mature at about four years of age and they live for about 8 to 12 years. They are able to absorb oxygen from the ocean water through their skin as they do not have scales. The antifreeze proteins that circulate through their bodies protect them from freezing and help them survive in waters with a temperature of around 28 degrees Fahrenheit. About 16 species of crocodile icefish live in the Antarctic region.
Icefish do not possess swim bladders. So, they spend much of their lives on the ocean bed. However, their lighter skeletons allow them to swim up into the water column at night to capture their prey. Icefish eat plankton—the floating plants, small fishes, and Krill—small shrimp-like crustaceans that live in oceans.
Significance for Humans
As icefish, too, has low mineral density in their bones like humans who suffer from osteopenia. Scientists are studying icefish to learn more about osteopenia and osteoporosis in humans. It also provides insights into other conditions such as anaemia in humans. The ability of the icefish to live in freezing water without getting frozen would also help scientists to learn about the formation of ice crystals and storage of frozen foods, and even storage of human organs for transplantation.
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