Do fish get thirsty when living in water?

Actually, fish do not really need to feel thirsty to drink water. Drinking water is just a reflex that happens without any decision from their body. So it can be said that fish never feel thirsty.

Whether fish are thirsty or not depends on their species. Because, saltwater fish and freshwater fish have different biological anatomy which leads to different behaviors in drinking water.

Saltwater fish and freshwater fish drink water differently.

Do freshwater fish drink water?

The salt concentration in the blood of freshwater fish is much higher than that of the surrounding water. Therefore, if freshwater fish drink water, they will face a high risk of thinning their blood. That is why freshwater fish do not drink water.

Instead, they use a mechanism called osmosis. Freshwater fish absorb water through their gills and skin. They also excrete much more diluted urine to get rid of excess water in their bodies.

How do saltwater fish drink water?

Compared to the surrounding water, saltwater fish have much thinner blood. Therefore, to avoid dehydration, saltwater fish must actively drink water. With the advantage of having special gills, saltwater fish can drink seawater, process and excrete all excess salt.

Saltwater fish always actively drink water in any situation.

What about fish that live in salt water and fresh water?

There are not many fish species that can live in both saltwater and freshwater environments. A typical example is salmon, which can migrate from saltwater to freshwater.

Salmon fry are born in freshwater, and they go through three major changes before they leave their birthplace and return home to saltwater. First, they drink a lot of water. Next, their kidneys reduce the amount of urine they produce. And most importantly, the mechanisms in their gills start working in reverse, removing instead of absorbing salt from the water.

When adult salmon need to return to freshwater to spawn, they spend a few days in an intermediate environment, called the tidal flats (shore waters or areas where the seabed is exposed at low tide). Here, their bodies reverse all of their juvenile transformations so they can survive in freshwater. So the answer is that biphasic fish drink water.

No matter what environment they live in, fish need to drink water.

Do other creatures that live underwater drink water?

Fish drink actively, but not because they are thirsty. There are two reasons for this seemingly reluctant drinking. First, fish basically live in water, so their bodies have no urgent need to drink water.

For fish, thirst is a reflex that occurs without any brain-controlled urge. It is just an instinct. They do not necessarily feel thirsty to drink water. We all know that these creatures, like all other creatures, need water. The question that needs to be clarified here is whether they drink water from their surroundings or not.

Tuyet Anh (Source: Synthesis)

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