text: why are saltwater fish not salty tasting? what is the chemical/biological process of saltwater fish that makes them unsalty?  what's the chemistry that makes this synthesis happen?  i'm guessing part of it starts with plankton and algae down the food chain.  but there still must be some processes that fish have that makes them not be salty. most vertebrates have their own internal milieu, that is, we maintain constant concentrations of ions and water that are different from those of the environment. this is achieved by means of the osmoregulatory system, which includes the kidneys but also, in the case of fishes, special excretory tissues in the gill area. some fishes (cartilaginous ones) do indeed maintain a high internal concentration of salts as part of their osmoregulatory mechanism:  it's not sodium chloride, however, but urea, and therefore their meat is stronger-tasting and has a salty smell.