Shoal of piranha swimming

The Social Behavior of Piranhas

With their reputation as a bloodthirsty and aggressive fish it’s easy to think of Piranhas as pack hunting predators constantly scouring the water for a meal. The truth, it turns out, is a little different.

In short the Piranha is far from a bloodthirsty monster portrayed in the films. They are scavengers, and swim in schools for security against their natural predators. They are very protective of their young, and will bite humans in the water to protect them, should you tray near a nest during mating season. The Black Piranha is a solo animal but many of the species, such as the Red-Bellied Piranha are school fish and swim throughout their lives in their own community.

The Social Behaviour of Piranhas

Piranha fish are very social fish that show signs of communication amongst themselves and other fish.  Some of the species, like the Black Piranha live as solo fish but many, like the Red-Bellied Piranha live in large shoals in the Amazon basin.

In captivity they will show similar schooling signs as they would in the wild as long as they are kept under the right conditions. They will be a little shy, as they are suspicious of their environment and other fish that live in the water space.

With their strong jaws and a ferocious nature painted by the Hollywood movies, the Piranha is surprisingly one of the most social fish and timid fish that fall prey to other large animals in the Amazon region.

They, however, are good at fighting back and have secured their place within the Amazon ecosystem as an essential part of the species that live in the basin.

a single red bellied piranha

Characteristics of a Piranha Shoal

A shoal typically has about 20 fish roaming together in a group. With Piranha there is the likelihood one or several fish will dominate the shoal. It was believed that Piranha fish schools were meant for hunting, but researchers and fish experts have recently disputed this claim.

Most of the Piranha species will swim together as a protective instinct against predators found in the Amazon region. There will be a definite leader or a dominant fish which is seen as an alpha animal, that might be larger than the rest, bold and more aggressive.

The dominant fish will take the best spot in the school, will be the first to feed and is seen as a powerhead in the shoal. The alpha Piranha fish will command the whole school, and any fish that do not corporate will be corrected through aggression, chasing and sometimes wounding.

Piranha Live in a State of Fear

Even when the fish are calm and in a peaceful environmental situation, they will constantly live in a state of predator awareness, as they have mutual mistrust for fellow Piranha fish. Piranha are known to be capable of wounding and possibly killing each other at the slightest provocation, usually driven by hunger.

Survival instincts call for the constant checking on each other. Knowing where others are within the school is essential. Not being aware could be fatal if they lose concentration on this issue.

In addition to mutual mistrust against their own species of Piranha, the fish  is prey to several predators in the Amazon, and their lives are in a tight balance of survival. This explains why Piranha that are captive are panicky and nervous despite being ferocious and aggressive in the wild.

How the Piranha Respond to Attacks in the Wild

One moment of carelessness in the wild for the Piranha would lead to loss of life as they are prey to jaguars, caimans, river dolphins, and alligators. The young Piranha falls prey to larger Piranha fish, especially when there is a drought in the Amazon basin leading to a scarcity of food.

A large animal, such as a dolphin, is much bigger than the Piranha, and it’s thought that Piranha swim in schools in order to provide security. The fish living on the outer edges of the school will scare the predator away, although they could be wounded, they know they have the support of the fish that live in the middle part of the school.

Those that are found in the middle part of the shoal will stay calm and give a strong comeback that will scare the predator away.

Piranha are also capable of ‘barking’, that is making sounds that warn a predator that they are prepared to fight back.

piranha swimming - man in background

How Piranha Catch their Prey.

Most Piranha are omnivores, and mainly eat fruits and plants. They will however, sometimes require a meat based meal.

Hunting food involves chasing and ambushing of their prey.  They will feed on smaller fish, amphibians, insects, crustaceans and smaller land animals in the water. The fish will rest under trees, where they catch falling fruits, bird eggs and insects.

They know when the young birds have hatched. They will, therefore, hang below the trees hoping that they might fall. If they fail to get their prey, they will feed on plants as they are well suited to adapt in these environments.

They rarely attack large animals as they fear that animals bigger than themselves would be predators. Humans are not a part of the Piranha diet unless the person appears weak or has drowned in the water.

Feeding Frenzy

Piranha show signs of coordinated communication during feeding frenzies. The fish on the outer part of the shoal will give way for those in the inner part of the shoal to have a bite. When they spot an animal that looks sick and weak, or even dead, one fish in the shoal will move swiftly have a bite and see how the animal reacts.

If it fails to react to the first bite, the rest of the shoal will swim and bite it and could strip the flesh off the prey especially if the shoal is very large and has been starving. During feeding frenzies, the water tunes red as the flesh from the weak or dead animal is stripped off by the fish.

Piranha will rarely attack large animals unless they think they are dead or very weak.

packed school of piranha

Cannibalism in Piranha

During the dry season when the Amazon region experiences scarcity in food for the fish, it is likely that the Piranha will show signs of cannibalism. They will bite off fins of fellow fish, and if the fish is severely wounded and very sick, they will kill it and eat in a shoal attack.

During mating season, which occurs at the onset of the rainy season in Amazon, these fish show signs of cannibalism as they are protecting their eggs and young ones from damage. When other fish pass near the nest, they will be injured and wounded which could lead to their death and cannibal behavior in the long run.

Finely Tuned Senses

A drop of blood will attract a shoal of Piranha from a good distance away. Piranha can smell a drop of blood in 200 liters of water. The Red-Bellied Piranha specifically, are meat-loving fish, and the smell of blood is an indication of meal time. When a shoal kills an animal, all the Piranha around the area will rush to the scene for a bite causing the much fabled feeding frenzies.

Their hearing is also heightened the sound of falling fruits will attract the piranha for feeding, piranha diet is known to be composed mostly of plant parts, unlike the belief that these fish are ferrous meat eaters.

Their lateral line is highly sensitive to waves and splashing of water which could be caused by animals that are drowning and could make a kill for the fish.

Parental Instincts

Unlike most fish, Piranha show signs of parental protection instincts. When they lay their eggs during the mating season in the breeding nest, they take an active role in protecting their young ones. During this time they are most aggressive and will fight any animal, even other Piranha fish that come close to their eggs or their young ones.

The male fish take a huge role in protecting the young ones. Once the females lay their eggs the males will fertilize them and stay guarding them against harm from the predators that live in their natural environment.

Once they are old enough, the juvenile fish will be hiding behind river plantation until they are strong enough to fight back and feel secure. Once they have grown into adults, some Piranha species like the Red-Bellied piranha will live in groups for protection against predators.

two piranha mating

Piranha Behavior in Captivity

Provided they get enough space with places to hide and dimmed lights Piranha can thrive in tanks. They will appear less shy and behave just like they would in the wild. Except for a few species, they are solitary animals that will prefer to live alone in their tanks.

They will show signs of aggression and are likely to be very territorial just like they are in the wild. The juvenile fish might look very different from the parents, and this could promote incidents of cannibalism in your tank.

Some, however, have coloration on the belly causing mimicry which prevents them from falling prey to their cannibal parents. To prevent the incidents of cannibalism, or to stop them attacking other fish that might be hosted in the tank,  Piranha owners should feed their fish frequently to prevent them from attacking the other fish that live in the tank.

If you put other species in there at all.

piranha swimming in a school

Protection of the Young Ones by Incorporation into the Shoal

Juvenile Piranha might find a spot in the middle of a school as a means of protection against predators. This is one of the ways that this species will survive, as they are many predators that could wipe out the young juvenile Piranha quickly.

Once they are old enough, the fish will leave the shoal to live in solitude or to form their own shoal. This behavior in Piranha ensures that there is continuity of species as the juveniles are groomed to grow into independent adults that procreate and ensure the continued survival of the Piranha fish.


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