Saltwater Aquarium Guide -- Fast Facts

Fast Facts (page 17)

What happens if you place a saltwater fish in freshwater, will it die? All creatures living in water are adapted to their surroundings and environment. This includes adapting to the effects of *osmosis. Seawater has a higher salt concentration than the body fluids of fish. Therefore, marine fish continuously lose water to the sea. The marine fish have to drink constantly, urinate very little, and push the salt out through their gills. Freshwater on the other hand has a lower salt concentration than the body fluids of fish. Freshwater fish never drink, the water tends to flow into their bodies. If freshwater fish drank even a little, they would swell up.

Fish in freshwater (water flows in)... Fish in saltwater (water flows out).

In both cases death tends to be from a few seconds to hours based on how permiable the skin is; marine fish tend to do better in freshwater because their skin is less permiable. But to find the answer to the question, you would need to kill alot of fish.

*Osmosis is the net movement of water across a selectively permeable membrane driven by a difference in solute concentrations on the two sides of the membrane.

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