piranha hiding in foliage

Why Do Piranhas Hide? – Troubleshooting Guide

In the wild, Piranha, whether a solo black Piranha or a schooling pygocentrus, have 360 degrees freedom of movement. They can choose to move or remain hiding and feel secure.

So, why do Piranha hide? In short, Piranha are a naturally shy and retiring fish. While they will swim, they are not domesticated animals and behave like they are in the wild. They have many predators, and too much noise, people passing by, inadequate room or lack of sanitation makes them skittish and timid. Getting the basics right of a proper sized tank with low level lighting, filtered water with plenty of decoration to help replicate their natural environment goes a long way to Piranha behaving more normally.

piranha hiding in plants


Hollywood and the media over the course of the last few decades have given some great misconceptions about Piranha. The portrayal of them as a bloodthirsty and mindless killer, that ferociously attacks anything in their presence is a complete myth.

The truth is that they are naturally a shy and timid fish, prone to skittishness. They will spend the day amongst the plants and taking refuge if they fear a predator may be about. They will not aggressively attack large animals in the water as a pack.

So, with an aquarium most layman or amateur enthusiasts might assume that the moment you place your hand in the tank, within seconds you will be missing a finger tip. There is a natural, but irrational fear that they cause injuries to owners.

Whilst it is important to be ever mindful when dealing with the fish, and not outright startle or frighten them into a defense attack, the common myth that they will mindlessly attack you is not true.

In a tank, they will be naturally shy, retiring and even timid. It is almost as if they are nervous and are immediately wary of anything unnatural that they cannot define as small prey that they can overpower. In the wild, the Red-Bellied Piranhas, despite being the most ferocious, will stay in schools for defense, not to hunt as a pack.

Almost all known human attacks come from humans wading in their nesting territory, or being injured or dead before the Piranha arrive. Many drowning victims become a feast for Piranha, but swimmers will not.

Additionally, Piranhas tend to nip. There have been rare cases where digits are missing, but mostly it is just flesh injuries by a single bite, not a school. In the most deadly attack of the last decade, when 70 injuries took place, there were no fatalities and everyone walked out the water.

So, if you get piranhas are a pet, be prepared to get asked ‘what happens if you put your hand in the water? A lot?’.

Everybody tends to think the tank would just turn red within seconds. However, the reality is rather different. They often just swim to where they feel most secure, and hide. They really are cautious fish.

The fact is that Piranha hide quite often, for a multitude of reasons. It could be because they are new to the tank, are still wary and are not eating. However, there are some more common and easily diagnosed reasons why your Piranha might be trying to hide, and it’s not because they have become bashful.

3 piranhas face on

Troubleshooting Why Piranha Hide

If you have just put Piranha in your tank, it may be because they are just getting used to it. Everything is new and they are working out what is going on. They are doing so from a safety point of view.

Assuming you have the basics right, like appropriate tank size, clean water, correct temperature with adequate cover and decoration for the Piranha, here is a small list of what might be happening.

Stress: When a Piranha is introduced to a tank, the whole environment is new. While it’s natural for them to hide away initially, they should eventually come out as they get to trust their new home, especially for feeding. Although it’s common for newly homed Piranha to not eat. Persistent and pervasive hiding though and something could be wrong. Do the basic checks of adequate tank size (20 gallons per fish), clean water, water temperature and varied diet feeding. Make sure you don’t have too many fish.

Lights: Piranha normally exist in low light conditions, and Piranha on display, want to be, well, displayed. Thus a common problem (and you see this on youtube a lot) is inappropriate lighting. People have very bright bulbs illuminating the whole tank. Piranha have large eyes with no eyelids so cannot shut out light. They may be hiding from painful light exposure. Try lowering the illumination to a more acceptable level and see if this coaxes them out.

piranha square on looking at you

Constant interruption: Piranha rest as well as having active periods. The temptation is to keep putting things in the water, especially as you try to get the tank setup right. This constant moving around in the water causes an already skittish fish to remain in hiding. Give them a period of acclimatization. Constant hands in the tank naturally unnerves the water which the Piranha interprets as a predator.

Sociability: Some Piranha are schooling fish and require more than one fish to be comfortable. Others, like the black Piranha are solo fish and other fish in the tank aer therefore unnerving. Make sure you have the appropriate fish for the tank. Red-Bellies require company to form schools for defense. Without it, they may hide. Two fish can sometimes fight for dominance. 3 Red-Bellied Piranha is the minimum. When there is a school, they may become more active. Remember, with Red-Bellied Piranha hiding is normal behaviour, especially when there isn’t enough of them.

Dominant fish: Like any animals a ‘pecking order’ may be being established. Once this has been worked out then things may calm down.

Tank location: Often overlooked as a cause of problems is where the tank is located. Firstly, is it in direct sunlight and the fish are getting too much light. Is it too noisy, bright, or is there no day or night routine because of strange lighting. Again, most people want to display their Piranha but the Piranha needs to live. If the tank location is somewhere where everybody passes it every minute or two, then this can cause issues of safety for them. Is a door being slammed to often that shakes the tank. If the environment is not peaceful for them, don’t expect normal behavior.

piranha face on close up


The thing to bear in mind with Piranha is that they are naturally skittish, timid and shy. Hiding is a natural part of their existence. In the wild they are food for humans, caimans, birds, turtles, and the ever present river dolphin.

Piranha in their modern variety have been around for just under 2 million years, and that is 2 million years of evolutionary history trying to evade predators. Their nature has served them well.

You can try a few different things and it always good to experiment and find out what works. Some people have had success putting tannins in the water to murky it a bit. Some people try a lot of foliage and plant matter and overhead cover. Trying to replicate their natural habitat is never a bad idea. Given time, this strategy should work.

Always make sure it is not a normal fear based reaction. Too much outside noise or light, or a tank with little or no decoration for hiding will produce skittish and fearful fish. Some people remove their decoration to force them out into the open and this is never a good idea, as you now have stressed fish.

Ironically then, provide adequate cover and break up sight lines with foliage so that it looks natural. With plenty of places they can move to should they feel it necessary, the more likely they are to come out, knowing there’s somewhere safe to retreat to.

Finally, Piranhas are not domesticated animals, they live as if they are in the wild throughout their lives. Give them adequate room, plenty of clean water with filtration, keep them well fed and you should see happy Piranha.


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