Complex animals, even fish, may be living in a lake under 2 miles of Antarctic ice, say Russian scientists who\'ve collected samples from its waters. Researchers who have analyzed genetic material in ice drilled from close to Lake Vostok\'s ice-covered surface said it yielded signatures for organisms such as bacteria often associated with marine mollusks, crustaceans and even fish, the BBC reported Monday. But writing in the journal PLoS ONE, the scientific team acknowledges the material may also represent past contamination. Scientists have determined the Antarctica ice sheet covers a complex network of rivers beneath it and many of the identified organisms, or their traces, perhaps have been delivered to Vostok from the ocean, the researchers said. The lake is thought to have been isolated from the surface and from the atmosphere for millions of years. The genetic material recovered included some \"associated with annelids, sea anemones, brachiopods, tardigrades and fish,\" the Russian researchers said. Lake Vostok, like numerous other sub-glacial bodies of water under Antarctica\'s ice sheet, is kept in a liquid state by heat rising from the bedrock below and from the pressure of miles of ice pressing down from above. Astrobiologists say conditions in these hidden lakes may be similar to those in the liquid water bodies thought to exist under the surfaces of icy moons in the outer solar system, like Jupiter\'s moon Europa or Saturn\'s Enceladus. Such places may be some of the best places beyond Earth to search for alien organisms, they say.