Fish regulate their water balance through a process called osmoregulation. Osmoregulation involves maintaining the proper balance of water and electrolytes in the fish's body relative to the water surrounding the fish. Fish have specialized cells in their gills and kidneys that help them regulate their water and electrolyte balance. They also have specialized organs, such as the swim bladder and kidneys, that help them adjust to changes in water pressure and salinity. Fish can also regulate their water balance by drinking or excreting water, depending on the needs of their body.