Here’s today’s kgb fact of the day:
Do fish urinate?
Fish have to rid their bodies of excess water by constantly excreting a weak urine. Freshwater fish can urinate 30 percent of their body mass/day.
More details:
In saltwater solutions, salt diffuses from areas of high concentration to areas of low concentration. Conversely, if a membrane blocks the salt from moving (but not the water) the water will diffuse from the low salt areas to the high salt areas. This is osmosis.
All creatures living in water are adapted to their surroundings. This includes adapting to the effects of osmosis. Seawater has a higher salt concentration than the body fluids of fish. Therefore, fish in saltwater constantly lose to the sea. These fish have to drink continually, urinate very little, and push the salt out through their gills.
Freshwater has a lower salt concentration than the body fluids of fish. Fish living in freshwater never drink. Freshwater tends to flow into their bodies. If freshwater fish drank even a little, they would swell up.
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Sources used:
http://www.fishdoc.co.uk/water/osmoregulation.htm
