Can Clownfish Survive In Freshwater?

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The first question that popped into my mind when I started raising clownfish was whether or not they can survive in freshwater. That was because I had already gotten used to freshwater creatures and wanted to use the skills I already had. That got me researching that topic a little deeper.

Clownfish cannot survive in freshwater, primarily because they are accustomed to hypertonic conditions found in saltwater. Introducing hypotonic solutions such as freshwater to clownfish would inflate their body cells and end their lives. That is in opposition to Euryhaline species, who may live both in fresh and salty environments.

As we move forward, I will go into the mechanism that may prevent your clownfish from surviving in freshwater. Also, I will answer whether or not clownfish may get accustomed to freshwater, and what are the main differences between freshwater and saltwater fish tanks.

Also Read: Clownfish Care Guide

Will Clownfish Survive in Freshwater?

No, clownfish cannot survive in freshwater. The misleading thought behind that assumption is that clownfish are quite easy to rear in a tank.

If you can give them a generously sized tank of at least 30 gallons (and plenty of places to hide), they should be fine.[1] Clownfish also eat any fish food you have on hand, including flakes, and live or frozen foods.

While larger fish might prey on them because of their size, they typically get along splendidly with smaller fish. They are also peaceful enough that you don’t have to worry about the creatures attacking their tank mates. This makes them the perfect fish for beginners.

However, because clownfish are sturdy and can survive in conditions that vary from their ideal parameters, some might think that they can force the creatures to live in freshwater tanks.

If you have some experience with fish, beginners have probably approached you about this same issue. Some could be asking, not whether clownfish can survive in freshwater, but rather, how they can force their clownfish to survive in freshwater.

One assumption is that an experienced fish owner can acclimate a clownfish to freshwater slowly, even though it is clearly a saltwater species. Another hypothesis is that clownfish that are introduced to freshwater at a young age could eventually grow accustomed to the conditions of a freshwater tank.

However, none of that is true. You cannot turn a clownfish into a freshwater creature. Introducing a particular species to a tank with the wrong conditions will cause the sort of physical distress that eventually ruins its health.

However, with clownfish, the situation is far worse. A Freshwater tank won’t make your clownfish sick; it will end their lives. It will do so quickly, in mere hours, not days or weeks. As such, if you are tempted to experiment with clownfish in freshwater tanks, you should know that you are condemning them to a painful fate.

There are no two ways about it. Clownfish cannot survive in freshwater tanks. Of course, when I make such blanket statements about clownfish, you are compelled to ask one question; why can’t clownfish survive in freshwater?

The answer to that question is somewhat complicated, and it applies to most saltwater fish. It also requires you to become familiar with a few new terms, as I will define later on.

However, for now, it is essential to note that saltwater fish are not the only creatures that find freshwater anathema. Freshwater fish are no different. They cannot survive in saltwater.

Some may think that fish can live in any kind of water. The assumption is that you can transport a fish from a lake to a pond and from a pond to an ocean, and it won’t make any difference. But that couldn’t be further from the truth. Most fish can only live in water with a particular composition, and taking them out of their comfort zone will probably kill them.

Why Can’t Clownfish Survive in Freshwater Tanks?

Regarding clownfish, there are a few terms you should get familiar with to understand why can’t clownfish survive in freshwater tanks. These would be osmosis, osmotic pressure, tonicity, and osmoregulation. 

1. Osmosis And Osmotic Pressure

To understand the aversion clownfish have for freshwater, you must first understand osmosis. The term refers to a process by which liquid molecules transition through a semipermeable membrane.[2]

To be more specific, osmosis refers to the movement of liquid molecules from an area of low solute concentration to an area of high solute concentration. A semipermeable membrane is basically a wall or barrier. It has holes that can permit liquid molecules to pass through it. 

  • In salty water, as in the ocean or saltwater aquariums, the wall will block the salt. However, water molecules are free to move towards the more concentrated side.

Regarding our case, you should know that the cells in your clownfish have a semipermeable membrane. That barrier permits the passage of smaller molecules while blocking larger ones.

Another variable in the equation is osmotic pressure. This term refers to the pressure that, when applied, counteracts the flow of water molecules across the membrane.

Osmotic pressure increases as liquid molecules transition from a low-concentrated solute to a high-concentrated solute. There is no osmotic pressure when the concentration on both sides of the membrane is equal.

2.  Tonicity

This term is concerned with the measure of osmotic pressure; specifically, it refers to a solution’s ability to exert osmotic pressure. If all of that sounds confusing, merely keep in mind that it has three main classifications:[3]

  • Hypotonicity – This refers to a situation where a solution has a higher concentration of solutes inside the cell than outside.
  • Hypertonicity – Here, there is a higher concentration of solutes outside the cell rather than inside. 
  • Isotonicity – Here, the solute concentration inside and outside the cell is the same. 

With isotonicity, there is no movement of liquid molecules across the membrane. With hypertonicity, on the other hand, liquid molecules are flowing out of the cell to dilute the high content concentration outside.

Hypotonicity draws water into the cell to dilute the high content concentration inside. With hypertonicity, the cell will shrink because it is losing water. With hypotonicity, the cell will burst because it is filled with water.

3. Osmoregulation 

This term is concerned with the steps that fish take to maintain the right amount of water in their bodies. They can’t have too much water or too little. Either extreme condition is dangerous. One way clownfish osmoregulate is by peeing. This might come as a surprise to some of you who had no idea that fish urinate.

Clownfish’ Case

If you are wondering how all these terms relate to a clownfish’s ability to live in freshwater, it all comes down to the fact that the creatures live in hypertonic water. Seawater is hypertonic. The concentration of salt is higher outside the cell (in the water) than it is inside the cell.

As such, water is always being drawn from the bodies of the clownfish. Fortunately, saltwater fish can osmoregulate by drinking more water than the quantities being sucked out of them. This ensures that they always have enough water in their bodies.

However, seawater has a high salt content, and there is a limit to the amount of salt that most living creatures can absorb. Fortunately, the gills and kidneys of saltwater fish are designed to filter the excess salt out of the water they drink via urination.

With freshwater, the reverse is true. Freshwater fish live in hypotonic environments where the salt concentration in their bodies is higher than the salt concentration in their water. As such, water is continuously drawn into their bodies.

Saltwater fish have to keep drinking water to maintain a balance in their cells. Freshwater fish, on the other hand, have to keep urinating to prevent their cells from bursting with water. 

If you are following this line of reasoning, you are probably confused. If freshwater fish prevent their cells from bursting with water by urinating frequently, why can’t clownfish do the same?

The answer is simple; clownfish are accustomed to hypertonic conditions. If you placed them in freshwater, their cells would take in the water at a faster rate than their bodies can eject it through urination. They would die all the same. 

Can Saltwater Fish Adapt to Freshwater?

Most fish can only live in either saltwater or freshwater. That is the case of clownfish. However, some species, called Euryhaline species, can survive in both environments.[4] You will see them migrating back and forth between freshwater and saltwater bodies.

Among the Euryhaline species, you have anadromous fish like smelt, salmon, and sturgeon, which are born in freshwater bodies.[5] However, they only come back to freshwater when they need to spawn. Otherwise, they spend most of their time in saltwater. 

Catadromous fish like eels do the opposite. They spend most of their time in freshwater, but they will invade saltwater whenever they need to spawn. 

However, if you have euryhaline fish on your hands, you cannot only move them from a saltwater tank to a freshwater tank and vice versa at a moment’s notice. They need time to acclimate to the salinity levels in each new tank. 

Are Saltwater Tanks Different From Freshwater Tanks?

Some people want to make the switch from freshwater to saltwater fish, but they don’t know if their experience with freshwater tanks matters when it comes to saltwater tanks. In truth, the differences are minimal:

  • First of all, metal screws that are exposed to the saltwater are going to present a problem because the salted water will destroy them.[6]
  • If your light fittings are not waterproof, the saltwater could also ruin them in the long run.
  • You are going to require a substrate consisting of sand or crushed coral. This is what your clownfish prefer. Sand is also encouraged because it maintains high levels of alkalinity.
  • Freshwater filtration systems will work in your saltwater tank. Though, it is worth noting that saltwater aquariums require more filtration than their freshwater counterparts. 
  • The lighting doesn’t have to change. While lights with a higher kelvin might increase the survival rates of your coral, you can still get by with your old lightning. 
  • You can keep your old pumps; the same goes for your aquarium heaters and decorations. The only significant difference will come in the form of the instruments you were using to measure the parameters in your freshwater tank.

Clownfish have different parameters that must be tracked. That being said, for the most part, with some effort, if you successfully maintain a freshwater tank, you shouldn’t have a problem creating and maintaining a habitat for clownfish.

What Does a Clownfish Need to Survive?

As was mentioned earlier, clownfish are quite easy to keep. They are likely to consume the typical fish food like pellets, and will also do just fine with algae, zooplankton, worms, and small crustaceans.[7] Therefore, food isn’t a big issue.

However, clownfish require both saltwater and hiding spots to survive. High salt concentrations prevent their cells from swelling while hiding places keep them safe from predators, such as relatively larger fish. 

That is particularly true in the wild, where danger is consistently nearby. Luckily, they do share a beautiful symbiosis with anemones. While they are likely to consume predatory fish, anemones ignore clownfish and even benefit from their presence. 

I have elaborated on that phenomenon in a different article, where I discussed whether or not can clownfish survive without anemones. To your surprise, in fish tanks, that symbiosis isn’t entirely necessary.

Still, for your convenience, I mentioned there what kinds of clownfish are likely to host which anemones. That will undoubtedly make your fish tank much more appealing. 


Clownfish cannot live in freshwater; there is no way around it. Introducing them to saltless tanks will end their lives almost instantly. That is because of osmosis and their natural living habitat in the wild. Do not experiment with this. 

That is in opposition to fish like smelt or salmon, which are Euryhaline. These kinds of fish may adapt to a different environment, although they require a gradual adaptation. 

However, that shouldn’t scare you. Saltwater tanks are pretty similar to freshwater ones, with merely several changes required. Either way, I wish you the best of luck in raising your clownfish. I’m sure you will do just fine and be able to enjoy these beautiful creatures.