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Do fish drink water? | Do fishes get thirsty?

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Hello Gnees Army,

Good Morning,

We all know that too much salt is bad not only for humans but also for animals (almost). So consequently, an animal that drinks seawater which is too salty must have a way to get rid of this excess salt.

Don’t ever think that seawater will fulfil your thirst. No matter how thirsty you are, drinking seawater will only make you thirstier. This seawater holds about 3.5% salt by weight. This amount of salt is good enough of dehydrating you because the amount of water needed to flush the excess salt from your body would be more than what you drank.

But luckily, many animals that live in or near the ocean or coastal areas have developed/accommodated the ways to pump out that extra salt keeping water levels of their body in balance.

Before we know this answer we should ask another question, really do fishes get thirsty? The question may look weird, isn’t it? Let’s see an example.

If we live in the world of chocolate should we have to hungry for it as there are chocolate and chocolate everywhere. Likewise, if fishes live in water, do they have to look for drinking that water, as we humans do to fulfil our thirst? Here, then another question comes here …

Do fish drink water
Do fish drink water

Why we feel thirsty? 🙄

The simple answer of this is – The reason we humans have to drink water is that we need a solvent to dilute everything (food) going on inside of us. All the chemical reactions in our bodies need a liquid to make it all happen. In simple words, we as well as mammals drink water as part of the physiological control mechanisms they use to maintain salt and water balance.

That’s why we choose water as solvent as it is most cheaply available solvent all around the world and almost 71% of the Earth’s surface is water-covered.

However, in short, in general, freshwater fish don’t drink water where saltwater fish drinks. But how? Let’s know from the below. So here we go…

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Saltwater fish

Where saltfish live in, there the concentration of salt in the water is higher than the concentration of salt within their bodies. Then the process called Osmosis* comes. As the body of a saltwater fish is less salty than the seawater it swims in – means it has a lower concentration of salt. So these fish actually lose water through osmosis which passes from their body, through their skin and gills, out into the sea. This puts them at a constant risk of dehydration which seems ironic as they live in water.

To protect this, the saltwater fish must actively drink water through their mouths. Thus, mostly saltwater fishes are seen to drink water to hydrate their body. They process the water and then produce small amounts of salty urine as well as secreting salt through specialised cells in their gills.

Most saltwater fishes have kidneys, by this, they process the water and pump excess salt into their small amounts of salty urine. Then they pee this salty into the water and can get it out of their bodies. They also have special cells in their gills that pump excess salt out into the sea. Combining these two systems saltwater fish can stay hydrated by drinking water actually as we do.

*Osmosis: It is the process where molecules move from a solution of high concentration to an area of low concentration. These molecules move through a semi-permeable membrane in a way which does not require to put any external energy. It’s very useful in order to equalize the concentration of the solution on both sides of the membrane.

Freshwater Fish

You might be wondered and interested in knowing that the opposite of this happens in freshwater fish. Water flows into their body through osmosis, instead of out. This means they don’t generally need to drink – but they do have to pee a lot.

If they drink does that mean they get thirsty?

What if they don’t control this?

Both freshwater and saltwater fish have to keep a certain concentration of salt in their bodies. Similarly, both have to take a certain amount of water. They can’t just allow water or salt to flow through their gills constantly. If they did, they would risk over diluting their blood and unbalancing the salt-water balance within their bodies. That is to say, it may cause saltwater fish shrunk and freshwater fish to explode.

To stop this phenomenon, their gills have special cells that selectively pump salt in, or out of their blood.

In freshwater fish, the cells constantly pump salt into their body.

In saltwater fish, they constantly pump salt out. They have kidneys which also help to filter out some of their salt.

Both saltwater and freshwater fish have to control the amount of water and salt in their bodies, to stay healthy and hydrated.

Example of another species who can drink saltwater – MEET THE ALBATROSS!

A wandering albatross spends many weeks during their flying or floating on the open ocean, far from any source of freshwater. As seawater/ocean/marine water is too salty for most birds and land animals, albatrosses have evolved a way to drink that seawater. But how?

Albatross Salt Gland
Albatross Salt Gland (from

To get rid of excess salt from the water and food they ingest, albatrosses have salt glands just behind their eye sockets. The glands discharge a highly concentrated salt solution that drains out from the tip of the beak.

To sum up,

Freshwater Fish VS Saltwater Fish
Freshwater Fish VS Saltwater Fish

Freshwater Fish VS Saltwater Fish

Freshwater fish don’t actively drink water because it dilutes their blood or fluids. The challenge for a freshwater fish is different than a saltwater/marine fish. For freshwater fishes, the blood and tissues are much saltier than the external environment and thus water follows into their body by osmosis process.

To counter this, the kidney of a freshwater fish discharges a lot of water from the blood and creates very dilute urine which always peeing out into the water. Besides, at this same time, their gills are constantly pumping salts back from the water into the body using the specialized salt cells.

On the other hand, saltwater or marine fishes have to drink water through their mouths to keep them hydrated. But here the incident becomes the opposite of freshwater fishes is that instead of discharging water, they discharge salts. Because they lose water for the saltier environment surrounding than them.

Consequently, their kidneys remove these salt and conserve water while the salt cells in their gills pump salt into the water. Using these opposite but useful tricks of passing salt and water, the bodies of marine and freshwater fish are equally hydrated and salty.

So, hope you have clear ideas about Freshwater Fishes and Saltwater Fishes, Do fish drink water?  Do fishes get thirsty? Hope you enjoyed this post. Thanks for reading! See you soon 😉

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