Do Fish Get Thirsty?

Do Fish Get Thirsty?

Every animal needs some amount of liquid in their body to be hydrated, and fish are no different. They may live in the water, but do fish have the ability to feel thirst or become dehydrated? The answer is yes. Fish can develop dehydration if their body salt content is off, much like humans. They may not feel thirsty like mammals do, but their body does send a signal to their brain that they need to balance the salt content within their body so they will increase or decrease the amount of water they are consuming. 

Do Fish Really Get Thirsty?

This may sound like an unusual question any curious child would ask. It makes sense because we feel thirsty when we do not drink enough water, and fish live in the water. We know that there is water within their body, and the circulatory system is similar to ours because it filters and moves blood throughout a fish’s body. All of these functions require liquid like water in order to function.

But do fish actually experience thirst? They are surrounded by water, so if they ever did, all they would have to do is open up their mouth to drink the water surrounding them, and they would be fine, right? The truth is that scientists aren’t so sure. It is extremely difficult to ascertain the needs of animals, especially if they’re not as expressive as those are cats and dogs. We currently are still discovering new ways our pets communicate with us, and these animals are extremely expressive. So it is so difficult to determine how a fish thinks and feels. There are far more factors that come into play when a fish requires hydration. 

How Fish Know They are Dehydrated

Fish do experience dehydration, and when their body is dehydrating, it sends a signal to their hindbrain, which tells them to drink water. However, the feeling of thirst and the state of dehydration are different. So they can experience dehydration, but they may not be able to experience actual thirst.

Can Fish Drink Too Much Water?

Every time a fish opens up its mouth, it does not mean that they are drinking water. Remember that everything a fish eats and drinks goes to their digestive system, just like land animals. And fish must also regulate their body and the amount of liquid that is in it. Like any animal, their bodies must have a certain amount of minerals, vitamins, percentage of water, and salt. If they are continuously drinking water without preventative measures, they can quickly die within the first day of being born. Obviously, there are preventative measures in place because there are billions of fish all over the world.

A Note about Salmon

Salmon have migratory patterns that cross between saltwater and freshwater. So they are special fish that can answer a few questions about hydration and osmoregulation.

When a salmon crosses from a saltwater body to a freshwater body, they must take in order to adapt to their new environment. The fish must allow their bodies to adjust to the lower salt content in the freshwater source that they will be traveling through. They must also regulate the salt content within their own bodies so they will not die. Scientists believe that it is their thyroid that allows them to make the ship between freshwater and saltwater back again.

Can Fish Drink Seawater?

Yes, saltwater fish can drink seawater. If a freshwater fish tries to drink seawater, they might die. There is far too much salt within the sea, and freshwater fish are not used to such an extreme environment. Because of body regulation, all of the liquid inside a freshwater fish’s body would leak out into the extremely salty water in order to find a balance. This loss of water will cause freshwater fish to dehydrate and die.

Freshwater vs. Saltwater Fish

Many people would suspect that saltwater fish have a higher concentration of salt within their bodies simply because there’s so much salt in their environment. However, this is not true. It is actually freshwater fish that have more salt in their body, and as a result, they have higher blood pressure than saltwater fish. Because they need to maintain the higher salt concentration in their bodies, freshwater fish have been found to urinate quite a lot.

On the other hand, because of their low salt content and low blood pressure, saltwater fish need to retain what little salt they have in their bodies. They also have less salt in their blood than salt outside in the water. They are the opposite of freshwater fish. Saltwater fish do not urinate very much; this helps keep in the salt that they have in their bodies. They do not require as much salt as freshwater fish, so when a fish swallows sea water, the gills on their body do not allow the massive amount of salt in the water to go into their digestive systems. Instead, it is filtered out and then released. 


While scientists do not know if a fish can actually experience thirst, they can certainly experience dehydration. Even though fish live in the water, they cannot simply swallow water in order to be properly hydrated. They must maintain the salt and mineral content within their bodies, or else they could experience in balance. So there is a filtration system in their body that regulates the amount of water they take in. If a freshwater fish accidentally travels into saltwater, they could lose the salt in their body and die. If a saltwater fish travels in freshwater, their bodies will absorb so much water that they can explode.

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