Osmoregulation is the process of maintaining an internal balance of salt and water in a fish’s body. A fish is, after all, a collection of fluids floating in a fluid environment, with only a thin skin to separate the two.


There is always a difference between the salinity of a fish’s environment and the inside of its body, whether the fish is freshwater or marine. Since the fish’s skin is so thin, especially around places like the gills, external water constantly tries to invade the fish’s body by osmosis and diffusion.

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