female and male red bellied Piranha

How To Tell If Piranhas Are Male Or Female?

While you can own Piranha without any need to know if they are male or female, having an idea as to whether you might see breeding behaviour does seem like owners want to know about.

So, how do you tell if Piranhas are male or female? In short, although there are no external sex differences until they mature, a change can be seen in females when they begin to show a slight egg bulge. Therefore males are generally slightly slimmer if the Piranha are a healthy weight. During breeding the famous red belly of the Red-Bellied Piranha is slightly more pronounced in the male.


The Red-Bellied Piranha is a medium sized omnivore from Latin America, and is spread throughout the Amazon basin. They live in all the waterways and countries, including Brazil, Argentina and Venezuela.

They mature and grow quickly, growing around an inch per month for the first 8 months and then the rate of growth slows. They will eventually grow to around 10 to 12 inches, feeding on a varied diet of fish, insects, worms, fruits and seeds.

They are a robust and hardy fish, with razor sharp teeth and a powerful bite. With a healthy environment, a good food supply they will mature around 1 year into their life.

The Differences Between Male And Female Piranha

Specifically with the Red-Bellied Piranha, a fully grown adult, whether male or female their trademark feature is the crimson chest that fascinates onlookers.

In the male, the red chest, as they sexually mature is much more pronounced than in the female. The female Red-Bellied Piranha has a slightly duller red.

This difference exacerbates during reproduction. The male Red-Bellied Piranha will have their chest get slightly more blushed and red, while the females might get slightly dimmer. So much so in fact, there might be a slightly yellow tinge to the female Red-Bellied Piranha.

The female, as she has to lay around 5000 eggs during breeding will be slightly plumper around the belly, especially around the breeding season. Males are slightly slimmer.

female and male red bellied Piranha

Does Age Make A Difference – What Age Can You Tell?

Typically, when you can tell the difference between the sexes of Red-Bellied Piranha is most easily done when they are in adulthood. The difficulty of doing so is heightened as you move towards the extremes in life, both young and old.

When Piranha are young they tend to have a more silvery color all around. The Red Belly has yet to develop.

Likewise, as the Red-Bellied Piranhas age, the brightness of the crimson chest will fade.

Additional Facts

There’s very little additional ways to tell, as the rest of the Red-Bellied Piranhas body shape is remarkably similar, with silvery flanks and the same fins.

To complicate matters, the precise coloration of the belly can vary slightly from location to location. Red =Bellied Piranha in Venezuela might differ slightly than those from Guyana. So when telling males and females apart they will need to be from the same region to limit error.

4 red bellied piranha in an aquarium


Red-Bellied Piranha will not reach maturity until they are at least 6 inches plus or 1 year, There are many factors that help the growth and maturity of Piranha including a healthy diet, clean water and stress free living.

It’s possible to feed them a good meat based and protein based diet that will naturally accentuate their crimson red bellies. This will help differentiate between the sexes as much as possible. Although, when they are old it becomes less noticeable.

In many circumstances though, it can be very difficult (some might say impossible) to tell the difference, although in others the coloration can be quite pronounced.

As you can’t tell the difference between males and females until later in life, typically around 1 year, if you want to breed Piranha you will need a lot more than 2 Piranha. The idea of buying a lot of them and assuming the probability aggregates seems to be the best solution. Eventually you may be able to tell as female get slightly plumper than the males, given the same diet.

Breeding Piranha is a tricky thing to do. You will need a good deal of Piranhas, which as they grow means a very large aquarium in order to reduce cannibalisation. You will then need all the appropriate paraphernalia that goes with keeping these fish.

At the end of the day, unless you are intending to breed them, it might just be better to buy what you need and just enjoy taking care of this fascinating fish. Breeding happens rather naturally in this species, and you might be able to tell at the appropriate time.


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