Why don’t saltwater fish absorb the salinity of the oceans and taste salty?


Just curious as to why fish and other sea creatures that live in salt water are not overly salty when ingested? I would think they would absorb most of the salt they live and breathe in.

Edit: added the word overly

In: Biology

Water concentration inside a fish is higher than in the ocean itself because the ocean is so salty. As a result, most saltwater fish constantly lose water through their gills and skin. To get rid of excess salt, the fish’s kidneys pump lots of salt into its urine.

tldr; they piss it out

Homeostasis is required in all living cells between salt and water. This allows the cells to perform many functions. Too much salt and all the water will be pulled out of the cells to try to maintain this balance and the cells will die of dehydration.

Saltwater fish are able to expel excess salt in their urine and secrete it through their gills in order to maintain this balance.


Sharks and rays (cartilaginous fishes) actually do this. The body of the shark is normally isotonic to the seawater around it. This is known as osmoconformation, as opposed to osmoregulation as seen in other bony fish. Most marine invertebrates (i.e. most other sea creatures) are osmoconformers as well, although their ionic composition may be different from that of seawater.

In sharks and rays, they maintain their isotonic relationship to the seawater using urea and trimethylamine oxide (TMAO). The shark’s blood electrolyte composition is not similar to that of seawater, but maintains isotonicity with seawater by storing urea at high concentrations. Sharks are “ureotelic” animals that secrete urea to maintain osmotic balance. TMAO stabilizes proteins in the presence of high urea levels, preventing the disruption of peptide bonds that would otherwise occur at such high levels of urea.

Additional reading:

[Pang, 1977. Osmoregulation in Elasmobranchs](https://academic.oup.com/icb/article-pdf/17/2/365/6065335/17-2-365.pdf) (pdf link)

Uhm… They do taste salty?