Do fish drink water? What is Osmosis and Diffusion?

Fish is one of the most diverse animal life on the planet. It has a wide variety of species living in different bodies of water all over the globe. They are fascinating creatures, and we all know them because of their ability to live underwater. With this said, it might capture our attention on how a fish could live in aquatic places.

For starters, we probably all know that fish have gills that enable them to breathe underwater. However, there is one question that sometimes comes in mind when talking about fish – Do fish drink water?

This question may be quite simple, but it is not as simple as it seems. It is apparent that humans need to drink water to survive, and the same thing goes to most animals. This need is quite reasonable, especially since we live on dry land, along with other animals. But for the fishes, which live underwater, would it be the same thing?

Do fish drink water?

In general, fish doesn’t drink water – unlike humans, in which we drink water to satisfy thirst. They only ingest water as a part of their respiration, wherein it would undergo a particular process and end up releasing it mainly through the gills. Although, this process is only applicable to some fish since it depends on the species and the neighborhood where it lives. The intake of water helps them to separate the oxygen from it and not for any other reasons. When they ingest water, it also goes into the urinary tract the same as humans. After taking in ample amounts of water, they also urinate, in large amounts, to avoid making their body tissues watery.

For a better understanding regarding this process of circulating water in fishes, we will look into one process that fish use to absorb or drink water – Osmosis.

What is Osmosis?

First and foremost, osmosis depends on the species of fish and on what type of water they live. One thing to keep in mind is that osmosis is a process of balancing or equalizing a specific concentration. Highly concentrated water does not contain solutes, like salt or sugar. An example of water with high concentration is freshwater. On the other hand, water with low concentration contains high levels of solutes, like what we have in saltwater. When we place high concentrated and low concentrated water with a semi-permeable membrane in between them, it will show that the high concentrated water or freshwater, will move towards the low concentrated water, filling the gaps to make a balance.

In our case, a fish needs to have a proper balance of salt and water concentration in their body, and osmosis is what they need to maintain the equality between the two.

If a fish lives in freshwater, the concentration of salt in their body is greater than the salt levels in the water – thus, osmosis happens when water naturally flows inside the fish’s body. The reason behind this is that freshwater is an area with a high concentration of water, while the fish that lives in it has a lower concentration of water – which makes it saltier. This process does not require them to drink water purposely since they already have enough water passing through their bodies. However, since freshwater fish are always hydrated due to the constant flow of water into their body, they would need to pee a lot.

On the other hand, a fish that lives in saltwater apparently has fewer salt levels in their body compared to the sea. Because of this, they tend to continually lose water through osmosis – which is the opposite of fish living in freshwater. This process will allow their body water to pass through their skin and gulls, then into the sea. The osmosis of constantly losing water for saltwater fish will result in dehydration, that is why they need to drink water purposely to stay hydrated. However, when they drink water, it flows down into their kidney, just like humans. The kidney and gills are responsible for filtering the saltwater to make it safe for them to drink.

Furthermore, if we put a saltwater fish into freshwater, it would die because of osmosis. As mentioned earlier, the water with high concentration will continuously move towards the water with low concentration. Meaning to say, a saltwater fish has a low concentration since it has more salt in their body. When we put them in fresh water, all the highly concentrated water will flow inside the fish’s skin and gills, making them inflate like a balloon – then eventually die.

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