Fish, like other animals and plants, are affected by osmosis. Osmosis is a process that occurs when water passes through a semi-permeable membrane from an area of high concentration to an area of low concentration. In the case of fish, this means that if the water in their environment becomes too salty (high salt concentrations), freshwater will pass into the fish’s cells and tissues to dilute it; conversely, if there is not enough salt in their environment (low salt concentrations), then sea water will pass out of their cells and tissues to increase its salinity. This can lead to dehydration or even death for some species of fish as they become unable to maintain the proper balance between salts and liquids inside them. To help prevent this from happening, many aquarium owners use special products such as reverse osmosis filters or chemical additives that remove excess salts from their tanks so that the amount of sodium chloride remains below lethal levels.