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How fish conquered the ocean

Scientists at the University of Bergen, Norway have deduced how bony fishes conquered the oceans by duplicating their yolk-producing genes and filling their eggs with the water of life ?the degradation of yolk proteins from one of the duplicated genes causes the eggs to fill with vital water and float. This is the major solution realized by extant marine teleosts that showed an unprecedented radiation during the late Cretaceous and early Paleogene Periods. The work is a unique hypothesis that integrates the cellular and molecular physiology of teleost reproduction with their evolutionary and environmental history.

"The oceans have not always been filled with fishes as nowadays" says researcher Dr. Roderick Nigel Finn at the Department of Biology, University of Bergen, Norway. "To the contrary", Dr Finn says, "the fossil record shows that the ancestors of the bony fishes (teleosts) inhabited fresh water environments for at least 150 million years before they entered the oceans".

"Apparently, it was not until the Eocene epoch (about 55 million years ago) that an unparalleled and rapid burst of thousands of new marine teleost species took place as evidenced by their sudden appearance in the fossil records of marine sediments. The basis for this successful radiation is unexplained and has intrigued biologists for many years", says Dr. Finn and adds, "Our paper in PLoS ONE relates to the molecular solutions evolved among the teleost ancestors and provides a compelling hypothesis of when, how and why the teleosts succeeded in the oceanic environment. It is common knowledge that water is essential for life," continues Dr. Finn, "so it seems a surprising paradox that fishes that live in water should have a problem acquiring it. Yet it was this paradox that provided the trail of clues for us to follow".

"The physiological problems of reverting from a fresh water environment to the saline seawater is demanding for the water balance of fishes", says
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Source:Public Library of Science


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