Why can a salt-water fish live in a normal water tank?
Salt-water fish do not have the same adaptations to fresh water that fish used to living in these environments have, and the ion concentration in their cells, which is high, will tend to become more balanced with that of the fresh water. This will occur through the process of osmosis, in which water moves across the semi-permeable membranes of the fish’s cells to the area of high ion concentration, the inside of the cells. This will cause the fish’s cells to become over-filled with water and to burst or lyse like a balloon that is over-inflated.
