Fish shift salt pump, as reported in Science, vol. 308, p1715, 17 June 2005 and Journal of Experimental Biology, vol. 208, p2023. Some fish such as the Mozambique tilapia are able to live in salty water and fresh water because they can off load excess salt when they are in sea water and take in salt when they are in freshwater. The salt is moved in the appropriate direction by specialised cells that have ion pumps in their gill membranes. Ion pumps are large proteins that move charged particles such as sodium, potassium and chloride ions in or out of cells. Salt absorbing cells have sodium and chloride pumps on their outer surfaces which move these ions from the water into the cell and then into the fishes body fluids. Salt exporting cells have sodium and chloride pumps on their inner surface so they take salts from the body fluids into the cell. They then pump the ions out of the outer surface of the cells into the surrounding water. A group of Japanese and American scientists have studied developing tilapia embryos to see how the ion pumping cells change when they are moved from salt to fresh water. They found that when the embryos were moved from fresh water to salt they replaced salt absorbing cells with salt exporting cells. Furthermore, they had a pool of dormant cells in reserve that could be converted from one type of cell to another by shifting the ion channels from one side of the cell to the other when the surrounding environment changed.
Editorial Comment: Sceptics claim fish could not have survived outside the ark during Noah’s flood because they need to live in the water with the right level of salt. This built-in mechanism for adapting to changes in salt levels explains how fish could have survived the changes in salt levels that undoubtedly occurred during Noah’s flood. Today there are fish that are incapable of adapting from fresh or salt water. We suspect these fish lost the ability to change their ion pumping cells. These fish are less complex than those that can change and therefore are no help to the theory of evolution, but they do fit Biblical history of complex creation followed by degeneration. (Ref. adaptation, environment, homeostasis)