Water is utterly essential for all animals and most get it by drinking, but what about fish? Well a lot depends on the type of fish, says Stuart Blackman
Do fish drink water?
The body fluids of freshwater fish are more concentrated than their surroundings, so they take on water continuously through their skin, gills and mouth lining by the process of osmosis.
Not only do they not need to drink, they must get rid of the excess by producing large volumes of very dilute urine.
Seawater, though, is more concentrated than a fish’s body fluids, so marine fish lose water to their surroundings and must drink to replace it.
This means taking in large quantities of salt, which is removed from the blood by the kidneys and expelled from the body in highly concentrated urine. The rest is secreted by specialised glands in the gills.
Discover more fascinating fish facts
