When you hear the word “piranha,” you immediately imagine a scene from a horror movie: a school of bloodthirsty fish devouring their prey in seconds. But the reality is much more interesting. Aquarium piranhas, most often of the species “common piranha,” are not monsters, but first and foremost living creatures with their own character and specific needs.
Many aquarists keep them precisely because of this legendary reputation. They are interesting to watch, with their powerful, predatory appearance and unique behavior in a school. But it is important to understand that this is not a fish for beginners. Keeping them is a serious challenge and a big responsibility.
Before deciding on such a step, you need to study the issue thoroughly. They need a very large aquarium, clean water, special food, and the right neighbors (or more often, no neighbors at all). This is not a story for a small jar on the table, but for a full-fledged, well-designed large aquarium where piranhas can live long and without problems for their owner.
Habitat in nature
The red-bellied piranha was first described in 1858. The Latin name was given in honor of the Austrian naturalist Johann Natterer (1787-1843). There is much debate and disagreement about the classification of the species, so it is quite possible that the Latin name may change later.
The habitat of red-bellied piranhas is the Amazon River and the Amazon rainforest, the coastal basins of the Paraguay-Paraná rivers and northwestern Brazil, as well as the Essequibo River basin. The basins of these rivers are located in Argentina, Bolivia, Brazil, Paraguay, Ecuador, Guyana, Peru, and Uruguay.
It inhabits rivers, tributaries, and small streams. Also in large lakes, ponds, flooded forests, and plains. The red-bellied piranha is considered the most ferocious of all representatives of this species found in nature. In nature, it lives in schools of 20 individuals, which makes it easier for them to hunt without becoming victims themselves.
They feed on anything edible: fish, snails, plants, invertebrates, and amphibians. These fish live in huge schools that spend most of their time searching for prey. The fish is quite voracious. Therefore, it can only live in waters rich in fish. Most often, red-bellied piranhas can be found in shoals, in deep and murky waters.
Are piranhas dangerous? Aggression in nature and in aquariums
Based on movies and literature, we know that if we just dip our hand in water with piranhas, they will eat it in a minute. Well, maybe it's not that dramatic, but if there is any injury on the hand and blood gets into the water, piranhas can smell it from many kilometers away, and the whole pack will attack a person and leave only a skeleton behind.
Is this really the case?
First, we must understand whether piranhas are really extremely aggressive creatures that attack everything that moves in the water.
It may sound strange, but piranhas are very cautious fish that pose no threat to humans. There are many known cases of people swimming in water full of piranhas without harming themselves.
Jeremy Wade was the one who demonstrated this to the fullest extent. He put piranhas in a small pool and swam there while several dozen piranhas did not even come close to him. It turns out that piranhas, considered predators thirsty for flesh and blood, are actually quite timid fish.
They are known to prefer living in large schools, so if you see one piranha in the water, there are definitely more. However, they stay in schools not because it is easier for them to kill humans, but because they themselves are part of the food chain for other larger fish species. In a school, the likelihood of being eaten is very low.
Moreover, experiments have shown that when alone, fish do not feel as calm as when surrounded by others. However, despite their peaceful attitude towards humans, piranhas are real killing machines for other fish species that are lower in their food chain. Their powerful jaws are designed to bite and tear apart, while their strong, muscular bodies are capable of moving and jerking incredibly fast underwater.
A piranha's bite ranges from 67 to 320 newtons, which is quite significant for such a small mouth. It is the strongest bite among all fish (relative to their body size) and is three times stronger than that of alligators of the same size.
However, this does not mean that these fish never bite people or animals that fall into the water. Almost always, such behavior is not due to their aggressiveness, but to self-defense or abnormal weather conditions. Due to changes in the latter, their behavior changes dramatically from the usual.
By abnormal weather conditions, we mean the dry season, when rivers become too dry and many fish remain hungry in pools of water cut off from the main stream. These hungry predators gradually begin to devour their own kind and are likely to attack any creature that enters the water. Sometimes piranhas' tendency toward aggressive behavior is observed during spawning, when they attack humans or animals as an act of self-defense. However, such cases are quite rare.
Description
Piranhas grow up to 33 cm in length, but this is in nature, and in an aquarium they are much smaller. Their normal lifespan is about 10 years, but there have been cases where they have lived for more than 20 years.
Piranhas have powerful, dense bodies that are compressed on the sides. They are easily recognizable by their heads with massive lower jaws. Add to that a powerful tail and a body covered with scales, and you have the perfect portrait of a fast, active killer.
Sexually mature individuals are magnificent in their coloration. The body color can vary, but it is mainly steel or gray, with silvery sides and a bright red belly, throat, and anal fin.
Some also have a golden sheen on their sides. The young are more faded, with a silvery color and black spots scattered across their silvery bodies. Their gill covers, pectoral and anal fins, including the abdomen, are bright red.
Their predatory lifestyle has influenced the size of their eyes and nostrils. Piranhas have a keen sense of smell and can find their potential prey even in complete darkness among dense vegetation.
Piranhas are not the bloodthirsty monsters they are often portrayed as. They can live peacefully in an aquarium, especially if the right conditions are created for them: a spacious tank, clean water, a balanced diet, and a shoaling lifestyle. The main thing is not to tease them, not to keep them with small fish, and not to forget that they are still predators. With the right approach, piranhas transform from a scary legend into interesting and even non-aggressive inhabitants of a home aquarium.
Difficulty in keeping
Due to numerous myths about the bloodthirstiness of these fish, piranhas are rarely kept in amateur aquariums, although they require moderate care. At the same time, the fish is not demanding in terms of food and is fairly easy to keep in an aquarium.
However, I cannot recommend this fish to inexperienced aquarists. The fish is large and predatory, and even servicing the aquarium should be done with caution. There have been cases where piranhas have injured their owners, for example, during transfer. This is a truly predatory fish with very sharp teeth.
Most bites to aquarists have occurred due to carelessness, but it is still better not to put your hands in the aquarium unnecessarily. In addition, it is very demanding on water quality.
Keeping in an aquarium
Despite their reputation as bloodthirsty predators, red-bellied piranhas are very susceptible to stress and very skittish in captivity. At the slightest sign of danger, the entire school quickly disappears into dense vegetation. Young piranhas simply lie on their side and pretend to be dead.
Piranhas will always stay away from unknown objects in the aquarium. If the fish is not hungry, its first reaction to any object placed in the aquarium will be fear.
However, do not forget that you are dealing with a predator that is quite capable of injuring you if it tries to catch you. In addition, if you do not feed the piranhas for a month, by the end of that time they will be eating each other, and any object that falls into the aquarium will provoke them to attack.
Aquarium volume
Piranhas stay in all layers of water. Adult piranhas are quite large; even in an aquarium, they grow up to 20 cm. Considering that it is recommended to keep piranhas in schools of 4 or more individuals, the volume for such a school should be 400 liters or more. Keep in mind that as the fish grow, this volume may become insufficient.
Water parameters
The optimal water parameters for the aquarium are as follows: T 23-28°C, pH 5.5-7.5, GH 4-15.
Aquarium decor
As already mentioned, they are quite skittish, and to make them feel more comfortable, the aquarium needs places where they can hide. Various elements can be used to decorate the aquarium: stones, driftwood, live and artificial plants.
The main thing is that they do not have sharp edges. When fish are frightened, they often start darting around the aquarium and can easily injure themselves.
Ideally, you should create an aquarium for piranhas that resembles their natural habitat. This is a densely planted (with live plants) aquarium with several open areas for swimming, with dim lighting necessary for plants. In these conditions, piranhas feel more comfortable, become more active, and tend to exhibit their natural behavior.
Filtration
The most important thing in keeping piranhas is to always have clean water. Check the ammonia and nitrate levels weekly with tests and change the water weekly as well.
It is advisable to have a powerful external filter in the aquarium and to change the water regularly. This is because they actively litter while eating and eat protein foods that rot quickly.
The filter needs to be cleaned regularly, and more often than in other aquariums. The best way to know when it's time is, again, to test it. Don't forget that when cleaning the filter materials, you need to use water from the aquarium!
The way these fish feed puts a significant strain on the aquarium's biosystem. That is why powerful filters and a weekly water change of 25-30% are necessary. Other necessary equipment you will need is an aerator, a heater, and a lighting system. You can choose the lighting you like, as piranhas tolerate both dim and bright lighting.
The most important thing about keeping them (and the most interesting!) is observing them. Watch your pets, study them, understand them, and after a while you will no longer need to worry about them. You will see any problems as soon as they arise.
Behavior in the aquarium
In aquariums, piranhas do not attract much attention. They do not have bright colors (the general tone of an adult fish's body is silvery with black shades, with a reddish belly and glitter scattered across the body) or an unusual body shape.
Except for their teeth, which are extremely sharp blades, it is unlikely that these fish will attract the interest of aquarists. In addition, the behavior of piranhas in an aquarium is not particularly remarkable. Due to this specificity, they are not often kept in species aquariums without the company of other fish.
Cannibalism is common among piranhas, as it is among many other fish. Cannibalism is usually caused by an aquarium that is not spacious enough or a lack of food. If there are too many fish in the aquarium, they will inevitably bite each other. In this case, some of the fish die, while others survive thanks to their high immunity. In addition, their wounds heal fairly quickly. After just a few days, the bite is almost invisible.
Aggressive behavior is usually caused by the victim's inappropriate behavior from the perspective of its pack. This could be a sick or injured fish, and it does not matter whether it is a member of their species or another inhabitant of the aquarium.
Feeding
In nature, piranhas feed primarily on fish; in addition, they attack any mammals that swim or drink water, as well as birds that fly close to the water. In addition to fish, their diet includes insects, crustaceans, mammals, reptiles, and amphibians. Some schools of piranhas live under trees where birds build their nests at certain times of the year. They patiently wait for the moment when a chick falls out of the nest. However, when they gather in schools of more than a hundred, they can attack large animals such as herons or capybaras.
When hunting its prey, the red-bellied piranha relies on speed and surprise attacks. The entire school attacks the prey and eats it, with each fish acting independently of the other members of the school.
In an aquarium, red-bellied piranhas feed on protein foods – fish, fish fillets, frozen shrimp, squid meat, earthworms, and live mice. The daily diet should contain foods high in protein (fish, shrimp, worms) with some added plant components.
It is not recommended to feed them mammalian meat, as it is poorly digested by fish and leads to obesity.
Teenagers should be fed every day, and adults every other day or every day, but in moderation. However, to prevent obesity, they should have one or two fasting days per week.
When feeding on its prey, the piranha cuts through all soft tissue with its razor-sharp teeth and usually leaves the skeleton intact.
They eat quickly and chaotically, trying to eat as much as possible for future use. Small pieces of food that fall to the bottom of the aquarium are usually ignored. Therefore, it is recommended to feed them small pieces of food so that they can swallow it whole without tearing it apart. To maintain the red color of the fish, their diet should include shrimp or artificial feed containing ingredients that enhance the red color.
Compatibility
The question of whether piranhas can live with other species of fish is perhaps the most controversial. Some say it is impossible, while others successfully keep them with very small fish. Most likely, it all depends on a variety of factors: the size of the aquarium, the amount of plants, water parameters, the number of individuals, their character, how densely they feed, and others.
It is easiest to keep them with larger species: black paku, singing catfish, plecostomus, and pterygoplichthys. The latter two get along well with them, as they live in the lower layers and are protected by bony plates.
You can try other fish, but it depends on your luck. Some piranhas don't touch anyone for years, while others…
This fish is predatory and definitely not suitable for a community aquarium. They can live alone in an aquarium, but it is better to keep them in a school.
However, even in an established group, cases of aggression and cannibalism are not uncommon. As a rule, the largest and most dominant fish rules the pack. It occupies the best places and eats first. Any attempts to challenge the current state of affairs end in a fight or even injury to the rival.
Sexual differences
It is extremely difficult to distinguish females from males. Visually, this can only be done by prolonged observation of behavior, especially before spawning. During this time, males take on the most vivid colors, and the female's abdomen becomes rounded from the eggs.
So, keeping piranhas in a home aquarium is a serious and responsible decision. This is not a simple goldfish, but a large, active predator that requires special conditions. It needs a very spacious aquarium, powerful filtration, a special diet, and constant attention to water quality.
If you are ready for all the difficulties, observing piranhas can be a real source of fascination. Their shoaling behavior, refined movements, and even their peculiar character are interesting to watch. However, it is important to always remember their nature and never treat them as ordinary decorative fish.
Ultimately, piranhas are only suitable for experienced and knowledgeable aquarists who appreciate not only their striking appearance but also their unique behavior. They will become the centerpiece of your aquarium world, but they will also require your full commitment. Carefully weigh your strengths and resources before acquiring these amazing but demanding inhabitants of the Amazon.
