A cold fish

摘要

Some fish have special proteins in their blood to stop them from freezing to death-a remarkable evolutionary trait made no less so by the fact that biologists have known about it for some time. How this trait spread, though, turns out to be even more remarkable. If Peter Davies of Queen's University in Ontario and his colleagues are right, it demonstrates in fish an evolutionary mechanism hitherto seen mainly in bacteria, viruses and genetic-engineering laboratories.rnAs sea-ice develops, the briny water beneath it cools to -2℃. Whales, seals and penguins cope with the consequent danger of freezing up by burning vast amounts of food to keep their bodies warm and by insulating themselves with thick layers of fat. Fish, however, are not warm blooded, and are usually too small to support substantial fat layers, so they have found a different way round the problem. Many species that live in cold waters have special proteins in their blood which attach themselves to small crystals of ice and prevent these from growing to a size at which they would be dangerous.