piranha aquarium

How Many Piranhas Should I Put In My Aquarium?

When setting up a tank, getting the balance of the aquarium is paramount. Whether it’s water temperature or pH, getting it right, including how many fish should

So, how many Piranhas should I put in my aquarium? In short, the general rule is 3 or 4 Red-Bellied Piranha minimum in a 60 gallon tank and then 20 gallons per extra fish. There are exceptions, but this helps avoid territorial and dominance fights amongst the school.


With many different species of Piranha it’s obviously difficult to apply generalities that work in all situations.

Firstly, it depends on the species. If you want to own black Piranha, then it’s crucial you understand this is a solo fish. The black Piranha does not school and is one of the biggest Piranhas available to own. It will need a 60 to 75 gallon tank on it’s own. Putting a second fish in their will end in disputes and confrontations.

The Red-Bellied Piranha is by far the most commonly owned Piranha in the world. It’s the most aggressive, the most common, and thus what tends to be the Piranha that everybody wants to own. It also doesn’t grow seriously big, and is quite manageable in an aquarium. It’s an omnivore and will eat meat as well as fruits and vegetables.

As it is the most common Piranha to own, it is the fish that this post will center around.

There are also many different ways of aggravating the situation. Piranhas prefer low light, so if they are in direct sunlight and there is minimum cover then, without eyelids, this produces stress.

The object of how many Piranhas to put in a tank is to keep stress to a minimum, but there are additional factors to consider, not just tank size.

piranha swimming in an aquarium

Is There A Minimum Number For A Tank

Whilst the black Piranha is a solo fish, the Red-Bellied Piranha is not. It naturally schools in the wild in numbers around 20 or more. A schooling fish should have a small school in a tank.

So, yes, there is a minimum recommended for Red-Bellied Piranha in a tank.

The minimum tank you should consider for Piranhas is around 60 gallons. In a 60 gallon tank there should be around 3 or 4 Red-Bellied Piranha.

Red-Bellied Piranha should NOT be kept alone, and two fish seem to fight for dominance rather than swim together. At least anecdotally.

General Rule

Perusing online there is a lot of advice, and a pet store may offer more, and there will be a lot of different opinions out there. Many different strategies out there, but the general consensus is the bigger the better.

The figures given are guidelines for minimums. If you have a 200 gallon tank and want to put 4 Red-Bellied Piranha in it, then that’s fine. Despite the fact that you could put more in without conflict, at least generally.

The general rule is to put 3 or 4 Red-Bellied Piranha into a 60 gallon tank as a minimum and then at least 20 gallons per extra fish.

Thus, if you want to own 7 Red Bellied Piranha, 4 of them will go into a 60 gallon tank. The three extra fish will require another 60 gallons (60 gallon minimum +20 +20 +20).

Thus the minimum tank size for 7 Red-Bellied Piranha should be 120 gallons. If you can get a 150 gallon tank for the 7 fish, then that is even better.

piranha swimming in an aquarium

The 60 Gallon Tank

This is a typical beginner aquarium and is the minimum size for Piranha you should consider. Yes, if you only want 3 Red-Bellied Piranha, you could probably just get away with a 55 gallon tank, but remember the bigger, the better.

With a 60 gallon tank, you should only put 3 or 4 Red-Bellied Piranha in it.

The 75 Gallon Tank

Slightly bigger than the typical beginners tank, you should probably think about somewhere between 3 and 5 Red-Bellied Piranhas in a tank of this size.

The 125 Gallon Tank

This is quite a bit of a bigger tank and requires more thinking about, in terms of location, lighting and decoration.

However, in terms of the number of Red-Bellied Piranha to place in the tank it should be between 3 to 7 fish.

Overcrowding Piranha – What Will Happen

The above requirements are recommendations only. They are a guideline to help you avoid stressing problems amongst the Piranha. Sometimes Piranha keeping can feel a bit more like an art than a science, but there are no scenarios that can avoid unpleasantries.

One problem though is overcrowding, which you can control with careful planning. When you place little tiny fry into a 60 gallon tank, it can sometimes look a bit silly, especially when you compare them to guppies or tetras in a same sized tank.

But these are Piranha, and they will, or can grow quite quickly. It’s not unknown for them to add an inch per month and within 10 months you could have several 10 inch fish in your tank. If you overcrowd from the beginning, this could become a serious problem as they grow.

Piranha are a territorial and schooling fish. As their space diminishes, they will get more and more stressed. They will start to swim in circles to defend their space and confrontations and fights for dominance will ensue.

The recommendations above are to reduce this occurrence as they grow. If you see Red-Bellied Piranha swimming in circles, and gnashing their teeth then you may have put too many Piranha into the tank.

3 piranha swimming in an aquarium


Keeping Piranhas can be tricky at the best of times. There are a whole host of problems that can arise with these fascinating fish.

Adding to your problems by creating a scenario whereby your fish are stressed is something you can do without, especially when these fish have teeth.

There are no hard and fast rules, and there are always exceptions. If you look hard enough online, you will find people who have kept 7 Piranha in a 45 gallon tank and says it’s fine. Which may be true. For them.

These guidelines, are just that, guidelines. The general rule of the bigger the better when it comes to a tank applies especially to Piranha. They can be an aggressive fish if you give them the wrong conditions. A low tank volume is just scenario.

Getting as big a tank as you can manage will definitely be best. It reduces stress in your fish, and territorial disputes, as well as fights for dominance. It would be a shame to lose fish as they grow because of poor planning.

The health of the Piranha should remain a primary goal. If you have 55 gallon then you should put 3 fish in it, not 4.

There are plenty of examples of people putting in more Piranha than are recommended, but there are more likely to be problems as well. Get it right from the start.


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