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How Many Clownfish Can You Put In A Tank?

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As I was preparing my aquarium, the one question I had to know the answer to was how many clownfish you could put in one tank. I knew about their aggressive temper and hierarchy tendencies. Naturally, I wanted to stick to the ideal number without causing unnecessary stress. 

The ideal number of clownfish in a tank is two, regardless of its dimensions. Introducing more fish than that may result in aggressive behavior originating from the mating pair. On the contrary, keeping a single clownfish may result in a weary, depressed fish.

As we move forward, I will go into the details of why you should keep merely two clownfish in a tank. More than that, I will present to you a few useful techniques to mitigate the aggression in your aquarium. That may allow you to keep the peace even between a group of clownfish.

Also Read: Clownfish Care Guide

How Many Clownfish in a Tank? 

Most people believe that clownfish should be kept in groups. Some may even call you cruel for keeping individual fish alone in a tank. They are convinced that the fish will suffer from boredom and loneliness, just like humans.

Others argue that the fewer clownfish you have in a tank, the fewer incidents of aggression you will encounter. That, in turn, will make it easier to manage your aquarium. These owners are more than happy to keep a single fish on their own in a tank, and they see no point in saddling them with a partner. 

None of these opinions are technically wrong. But it all depends on the species of fish in your tank. Clownfish are one of the more complicated groups of fish. That is mainly due to their ability to change genders and establish a hierarchy.

As was mentioned above, clownfish can live alone. They can also live in pairs if that is what you want. However, you are discouraged from keeping more than two clownfish in a tank. Don’t even think about trying to introduce multiple breeding pairs of clownfish.

First of all, the average clownfish school consists of one female and multiple males; this assumes that you have numerous clownfish in the same tank. While there are rare exceptions, in most cases, you can only have one female in an aquarium.

Once that female chooses a mating partner, that pair will exert their dominance over the other males in the tank. This is why it is challenging to keep multiple clownfish. The mating pair will bully every other male in the vicinity.[1]

This aggression works in the pair’s favor. It keeps the subordinate fish small, preventing them from ever growing more substantial and dominant. This, in turn, eliminates the possibility of a subordinate male becoming a female. 

Male clownfish are not likely to show hostility towards a female. But if you introduce a female clownfish to a tank that has a mating pair, the two females will fight. You shouldn’t be surprised if one of them even dies. This is why you have to be careful about the number of clownfish you keep in your aquarium.

If you must have multiple clownfish, get a reasonable number like five. Anything less or more is going to lead to disaster. But even if you have the right amount of fish, be prepared to see your mating pair antagonize and bully their subordinates.

Admittedly, situations have occurred where a mating pair has existed in relative peace with the subordinate males. But the chances for hostility and aggression are far too high. Do clownfish need to be in pairs? No, they don’t. But it is the best way for them to live, short of keeping individual clownfish in a tank. 

Do Clownfish Need to be in Pairs?

Clownfish don’t have to be in pairs. There are circumstances when they will do just fine in groups (particularly in relatively large tanks).[2] That being said, clownfish thrive when you keep them in pairs. This way, they can pair, while holding back their aggression.

You can even keep clownfish on their own. However, I witnessed a few cases where the clownfish grew weary due to loneliness. Some also argue that their colors start to fade in response to the stress emanating from their isolated conditions.

However, there is no substantial evidence to support these claims. Barring some mitigating circumstances, clownfish can live alone. You don’t have to pair them if your situation doesn’t allow you. Merely experiment and see how your fish behave. 

What Happens When a Clownfish is Alone?

As you now know, all clownfish are gender-neutral at the start. It is only at a certain point in their lives when they become males or females. At first, if you place two clownfish in a tank, they will fight. Then, the dominant clownfish will become the female, and the submissive one will turn into a male. 

However, if you have just one clownfish in a tank, it will start leaning towards becoming a female. Since there is no companion to suppress it, there is no reason for the clownfish to turn into a male. However, as the sole fish in the tank, its gender doesn’t play any significant role. 

When you have a school of clownfish, the aggression of the mating pair keeps the subordinate males from becoming female. With a single clownfish, this suppressing force is absent. Therefore, nothing is stopping the single male fish from becoming the alpha female.

The Biology Behind Keeping Clownfish in Pairs

Clownfish are unique, at least as far as their gender is concerned. That is because they are hermaphrodites. People may tell you that they are born male. But they are actually gender-neutral at the beginning, neither male nor female.[3] 

Over time, they develop male gonads.[4] This happens to every single clownfish. There are no exceptions. If you have two or more clownfish in a tank, they will fight for dominance. The largest and strongest of them all will eventually develop female gonads. She will become the unquestionable ruler of her school in the tank. 

Blessed with the only body that can breed, she will choose a male, the second most dominant clownfish. After some semi-aggressive courting, they will produce eggs that the male will care for until they hatch. At this point, he will leave them to their own devices.

If the female clownfish dies, her partner, the most dominant male, will become the next female. He will develop female gonads, and take on a male partner (the second most dominant clownfish), and the cycle will continue. 

As you might have inferred from the information detailed above, clownfish are naturally aggressive. Their hostile mannerisms can be attributed to their hierarchical structure. Every school of clownfish has a single figurehead at the top, the female. 

She wins that position by proving her dominance over every other fish in the school. The same goes for her partner. When the female dies and her partner becomes the new female, every other fish below moves one step up in the ranking.

There is a particular order to the lives that clownfish live. But that order is brought about through violence. Besides their hierarchical nature, clownfish are also territorial. In the wild, they live in anemones that they have been trained to protect.

In an aquarium, clownfish are not the most territorial creatures you will ever encounter. But they will protect what they consider to be their domain. On a more positive note, their aggression is typically targeted towards their own kind. In fact, in many cases, their territorial behavior is most pronounced when you introduce new clownfish to the tank.

They are particularly aggressive towards clownfish of different species. They are less likely to aim their aggression towards other types of fish. They are technically peaceful animals that can live in harmony with other friendly creatures.

How to Control the Aggression Within Your Clownfish Tank

Some of you understand the importance of keeping clownfish in pairs. But even females in a mating couple have been known to bully their male partners. There is also the chance that some of you have multiple clownfish in your tank, and you wish to bring their violence under control. 

Regardless of your situation, the following tips are bound to prove useful:

1. Get the Right Tank

One way of quelling the violence is to get a bigger tank. A large aquarium reduces the probability of your fish fighting over territory. You should also add plants and decorations to give subordinate males places to hide. This will allow them to co-exist with more violent clownfish.

When it comes to sizes, you should aim for at least 25 gallons. That size may also allow you to introduce anemone to your aquarium. Due to the beneficial symbiosis between the two, your clownfish are likely to remain stress-free and less aggressive.

The one tank I wish I had and will probably purchase soon is the NUVO Fusion Lagoon 25 Pro (link to Marine Depot). I’ve been consistently hearing excellent reviews on that bundle, including its well-planned construction and amazingly quiet filter. This one should be large enough to place plenty of anemones, making your clownfish feel as in their natural habitat. 

2. Consider the Type of Aggression

First of all, you need to ensure that you are not overreacting. Clownfish are naturally aggressive towards one another. That is how they exert their dominance and create their pecking order. Don’t assume that things are going wrong merely because your clownfish are chasing one another around.

You should only worry when some of your clownfish start manifesting severe injuries such as ripped fins. You should also look for signs of stress. For instance, fish that are cracking under the strain of bullying will spend a lot of time hiding. These won’t eat as much, and their health will suffer in the long run.

3. Captive vs. Wild Fish

You should know that wild clownfish (that were captured in the wild and transplanted to an aquarium) are more aggressive than clownfish that were bred in captivity.[5] Wild fish are accustomed to fighting for their lives. Also, they do not stray from their anemone. 

However, their captive counterparts have spent their lives swimming freely in a tank. As a result, they are less likely to react aggressively towards other fish of the same or different species.[6] If you have a choice, endeavor to prioritize clownfish that were bred in captivity whenever you go clownfish shopping.

4. Feed Your Clownfish Right

Food is a common source of aggression among clownfish. Dominant males have been known to horde all the best nutrients for themselves. They do this to inhibit the development of subordinate males. Make sure you add enough food to the tank to satisfy all the clownfish. 

You should also scatter the food throughout the tank to allow the clownfish to feed without interacting with one another. Also, tanks with young fish need more food. This is because young clownfish consume more nutrients than their adult counterparts. 

If you feel unsure regarding that topic, I highly recommend that you read my article regarding how much and often should clownfish eat. I also mentioned the right type of food you should get for your clownfish to make sure they live long. 

5. Tank Conditions

Try to keep the parameters of the water within the appropriate range. The wrong pH, temperature, salinity, and hardness will exert stress on your clownfish. Stress can lead to aggression and fighting.[7] Keep your clownfish happy by maintaining a pristine tank. 

From my experience, one of the essential factors is water temperature. For your convenience, here is an article I’ve written regarding that topic. I mentioned there what steps you should take to make sure that the water temperature doesn’t fluctuate.

6. Choose the Companions Wisely

If you wish to keep multiple clownfish, avoid even numbers. For instance, it is better to keep five clownfish than four. When you have four fish, it is much easier for the majority to single out one fish to bully. You can dilute the aggression by adding more clownfish.

I also suggest that you put an anemone in your aquarium. There is a reason why these two creatures live in symbiosis. In nature, clownfish are being protected by the anemone tentacles from predators. That also includes clownfish that feature an aggressive attitude towards one another. 

On that matter, here is a useful article I wrote on how to make clownfish to be hosted by anemones. If you are new to this field, reading that would practically make you an expert. There are a few simple steps that you can take without any background to create a symbiosis much more likely to occur. 


The ideal number of clownfish per tank is two. The best way to balance between aggression and partnership life is by growing them in pairs. If you wish to keep more clownfish than that, you should get yourself a relatively large tank. Then, the ideal number would be a school of five. 

I hope my article has shed some light on your question. If you have any hesitation regarding your fish, feel free to contact me in person. I will do my best to get back to you as soon as I can.