The Thirsty Fish Myth: Debunked.
Fish do get thirsty, but they mostly absorb water through their skin and gills via osmosis. Saltwater fish are always thirsty and drink all the time, but they have specialized cells in their gills called chloride cells that actively push salt out of their bodies. Freshwater fish spend all their time trying to keep water out of their bodies and never drink it, but they have chloride cells that work by pulling salt into their bodies. Sharks maintain high concentrations of urea in their body to balance the incoming of water.