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?

Sodium is one of the main ions used in sending signals through the body. If they absorbed all the salt, they whould experience spontaneous generation of signals all over the place. This includes the heart and other organs. If your heart is doing its own thing and not beating in order, it is not pushing blood very effectively so cells are not receiving the needed nutrients in a timely fashion. Cardiac arrest is likely.

More importantly it fucks up their water balance. Water follows salt. If there is more salt in the fish’s blood, the water from their cells comes out and the animal dehydrates. Most marine animals either have reniculated kidneys or salt glands that are specifically suited for excessive ion environments. Sea birds have salt glands near their eye that empties brine out their beak, sharks have rectal glands that does that same thing but out with their feces. Marine animals spend a lot of energy of getting ions out of their body (freshwater spend a lot getting them in), and maintaining proper water balance

They actually do. If you taste a sea fish and then a freshwater fish immediately after eachother it is very easy to tell which one grew in a salty environment and which grew in a muddy environment. Honestly – try it!

All animals on Earth need salt to live. For example, animals with brains like humans use salt to keep their brains healthy and for controlling their body. But animals need the right amount of salt: too much or too little will hurt them.

Fish that live in saltwater are in a funny situation: saltwater has too much salt in it for their brains! So fish bodies have to take the salt out of the water they absorb, and put that salt back out into the ocean. If they absorbed the salt and kept it, their brains would have bad problems.

Everyone is saying that the salt get filtered out but I’m not so sure about that. I had shark once and it was too salty for me

There is a great “It’s ok to be smart” that asks if fish pee that answers this. https://youtu.be/ocl04cmGPSM

Saltwater fish are salty in my opinion. As other people have said though, they do expel some of the salinity through their pores.

Countercurrent flow. It’s been a while since I learned it but it’s a similar way to how the Nephrons in the kidney can concentrate solutes.

One of the foundations of life is pumping salt out of cells. We are all walking amalgamations of tiny regulated portable oceans.