How Many Piranhas Can You Have In a Tank? {Do They Like To Be In Groups?}

Are you looking to keep a group of piranhas in your tank? How many can you fit in there before things get out of hand and aggression turns into carnage? In this article, we’ll discuss the topic of keeping a certain number of piranhas depending on your tank size.

How Many Piranhas Can You Have In a Tank? One piranha can be kept in a 20-30 gallon tank, but they thrive in groups of 4 or more. You will need a tank over 60 gallons and preferably larger than 80-100 gallons for 4-5 of them. If you wish to keep many more piranhas, you will need a spacious tank or use multiple tanks. 

How Many Piranhas Can You Keep Together?

Piranhas are popular freshwater fish to keep in captivity if your country or state allows it. They are known to be ferocious or aggressive in popular media coverage or in pop culture, but they are actually a lot more docile in reality.

Piranhas will act shy, timid and slightly skittish in a spacious tank with plenty of hiding spaces and room to maneuver. They will get more aggressive and stressed if you try to cram too many piranhas in one tank together.

If one gets hurt or injured, the others may attack it. Tankmates who instigate aggression such as a cichlid my incite a riot or frenzy of aggression. Follow these tank guidelines for keeping piranhas:

  • 1 piranha: 20-30 gallon tank
  • 2 piranhas: 40-50 gallon tank
  • 3-4 piranhas: 60-80 gallon tank 
  • 5-6 piranhas: 100 gallon tank

Increase your tank size if you wish to keep more than 6 piranhas who tend to enjoy shoaling in schools. Most species (excluding the Black piranha) will be less aggressive in a group as long as there is enough room.

How Many Piranhas in a 75 Gallon Tank?

75 gallon tanks are a great size and very popular for many aquarists who have the room. More often than not, the red-bellied piranha turns out to be the most popular species of piranha to keep in captivity.

They prefer to be in groups of 4-6 to reduce aggression and make them feel safe. You will be able to stock 4 piranhas in a 75 gallon tank, but you will have to monitor their behavior.

If you notice aggression, excessive hiding, sulking, lethargy or lack of appetite, then you may need a larger tank.

3 piranhas are not as docile as 4. Since you should have at least 20 gallons of water for one piranha, fitting 4 into a 75 gallon tank could get slightly tight once they reach their full body size. Red-bellied piranhas can reach 15 inches at full maturity.

Can Piranhas Live Alone?

A single piranha may feel stress or lonely in a solitary existence. It may decide to:

  • refuse eating
  • become sluggish
  • succumb to poor health 
  • hide or sulk in a corner
  • become aggressive to other tankmates

If you would like to keep only one piranha, we recommend the Black Piranha which is also known as the Redeye Piranha. This species prefers to be solitary, but may also lash out at any tankmate you wish to keep with it.

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Can You Keep Different Piranha Species Together?

It is not recommended to keep piranhas of different species together. This is not going to mimic their natural environment and may lead to aggression.

They may not be able to school with each other. Keeping piranhas in a species specific tank is your best bet to limit aggression and stress.

You will enjoy watching your piranhas of the same species coexisting together and feeding naturally without competition or confusion when faced with other species in the same tank.

What Happens If Piranhas Are Overcrowded?

An overcrowded tank of piranhas means that you have more than one piranha per 20 gallons of water. Your piranhas could become:

  • increasingly shy
  • refuse to eat
  • territorial 
  • aggressive 
  • cannibalistic
  • erratic and swimming in circles

Add 4-5 piranhas to reduce the tendency to attack each other, but make sure you have a tank over 75 gallons to keep the peace. We offer suggested guidelines, but if you wish to give it a try with a 55 gallon tank, be warned that aggression may ensue.

Can Piranhas Live Together?

Piranhas can live together depending on their species. It’s generally a smart move to reduce aggression, timid behavior or even cannibalism by keeping them in groups of 4-6.

A Black Piranha would rather live alone. If you wish to keep a school of piranhas together, the most popular option is the Red-Bellied Piranha.

If you notice your piranhas doing nothing all day and acting skittish, increase the tank size or add more hiding spaces. They could be increasingly frustrated if you are unable to allow 20 gallons of water per piranha.


When you start to get into the hobby of keeping piranhas and you begin with juveniles, you can keep 5-6 of them in a 55 gallon tank.

They will soon outgrow this tank after starting out around 3 inches and quickly reaching 12-17 inches in length. At this point, you will move from 10-15 gallons of water per juvenile to 20-30 gallons for each mature adult.

We recommend keeping happy piranhas together in comfort when they are able to shoal in numbers of at least 4 or more. We welcome your feedback and experiences. Feel free to email us anytime!


Thank you for visiting for another article on Piranhas that we greatly enjoy taking care of in our aquariums. Check out more of our articles on the variety of aquatic life we research and keep. Good-bye for now!

Brian Arial

Brian Arial has kept fish for leisure and worked with fish stores for most of his life. He enjoys writing and caring for aquariums and ponds.

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