hey there!  welcome to the new episode of Curiosity! A series in which we will answer some of the questions that makes us all curious.  

Humans are dependent on very few things for eternity of their lives. In other words, it's likely impossible to survive without some important things. And from those few handful of things, water is one of the most important necessity for the existence of the mankind. It's just not possible to survive without water. Not only humans, in-fact all the land animals need water to survive and all of them get thirsty. But Have you ever wondered , do fish get thirsty? They are in-fact always surrounded by water all the time , so do they get thirsty? Let's find out.

Firstly, What's Thirst? 

The term "Thirst" simply means urge to drink water. There's nothing better than a glass of water when you are thirsty. Our body literally cries for water whenever it gets dehydrated in the form of thirst. This urge is our body's way of maintaining the balance of water and other electrolytes. After all, hydrated people look very healthy and fresh. Not only us, all the land animals have to survive dehydration, therefore each one of them have to look for water. 

Credits

But what about fishes? Is there any urge for them to drink water? do they ever feel thirsty like we do? 

We are talking about a totally different species. The species which spend most of their lives in the water. The fact is if we humans are provided with something for our whole life , then it just loses it's value. Imagine, what if you were supplied with burgers each and every day of your life. You would certainly start hating burgers after sometime. 

Same goes with the fish. If they are surrounded by water for most of their lives, how can they develop a strong urge to drink water or to get thirsty?

Well, to answer this we need to have a look at different types of fish. Fresh water fish and Sea water Fish.

Fresh Water Fish

As we know, fresh water doesn't have high concentration of salt. But the fishes living in the fresh water have higher concentration of salt in their blood than the surrounding water. Due to this reason , they have high risk of diluting their blood if they directly drink fresh water. This is why drink a very little water. This process helps in balancing the concentration of salt and water in their body.

So, these fishes simply absorb most of the water from their gills and through their skins by the process known as osmosis ans then urinate in the form of a dilute mixture to throw away all the excess water.

Fig: Regulation of Water in Fresh Water fish (Credits)

Osmosis is the phenomenon in which the molecules passes through a semi permeable membrane which in this case is gills and skin , from the lower concentrated solution to higher concentrated solution. Here, lower concentrated solution is the fresh water, and higher concentrated solution is the blood of fish. Well, if the water is only absorbed then the fish would swell so to compensate this, the kidney of the fish produces large amount of urine. Large amount of urine means loss of salts, so to compensate this, fish absorbs special cells (chloride cells) in the gills take different ions from the water and transports them directly to the blood stream.

Sea Water Fish

Fig: Water Regulation in Sea Water Fish (Credits)

The environment is exact opposite to the fresh water fish. The slat concentration in blood of the fish is lower than the surrounding water because the sea water is highly saline in nature. Because of lower concentration of salt in their blood , they have fear of getting dehydrated all the time, because  of the above explained phenomenon called "osmosis".So , the sea water fishes have to actively drink water all the time. Since their kidneys are relatively small , they secrete very small amount of urine. The Chloride cells in these fishes works in reverse manner , excreting the excess salts. Helping in regulation the Bodies salt and excess water is lost from skin.

So does that mean they are thirsty?

Probably not , The reason behind this is , unlike humans they don't need to seek for water all the time, they literally live in the water. This is why they sea water fish don't develop urge to get thirsty. Also, the another reason is all this process happens without any conscious action of the fish, it just happen on its own. So , they don't quite need to feel thirsty in order to drink unlike humans.

That's it for this Episode guys. Hope you Enjoyed it. If you did Up-vote and comment your thoughts below. Thank you

Stay Curious.

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References Used:

[1]- What is Thirst?

[2] - Do Fish need to Drink water?

[3] - Salt Regulation in Fish.

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