The Piranha is one of the most efficient predators on the face of the earth. Granted it is not a large animal, with most only reaching about 5 1/2 to 10 inches (14 – 26 cm), but it is known world wide for its ferocious nature. They have razor sharp teeth and are opportunistic carnivores.

A frenzied attack by a group of Piranha will set the water churning. They will attack and eat all sorts of aquatic animals, insects, lizards and amphibians. They will also devour rodents, carrion (dead meat), and sickly or weakened land animals that venture into the water.

The teeth of the Piranha are triangular in shape with an exact fit in their jaw, comparable to a bear-trap. They are designed to puncture and slice the flesh from their prey. They can strip their prey to the bone in a matter of minutes.

These fish are a great source of fascination. Their natural behaviors have become fodder for the scripts of moviemakers looking for a sensational twist to excite and entice an audience. What could be more intriguing than creating a ‘fear factor’ from the behaviors of these provocative fish found in the “wild”. Yet just like the Great White Shark and the Anaconda constrictor, also popular subjects of thriller movies, the Piranha’s behaviors are over-fantasized.

The Piranha does engage in a feeding frenzy that will “make the water boil” if only because a hungry school of fish are trying to reach the same limited food source. All that activity is bound to create water turbulence. A Piranha school generally only consists of about 20 or so fish, but in a feeding frenzy it can reach up to several hundred..

Piranhas are not always that deadly. Many species live solitary lives once they reach maturity and only four or five species pose any significant danger. Piranhas rarely attack people. Many experts believe they are actually timid fish, and shoal for protection. Even the most aggressive are thought to be not really dangerous until they are trapped and confined, and then attack in self defense. As a pet they are fascinating and beautiful fish, yet you can’t hold or pet them. They are not affectionate and owners must be extremely careful, especially when handling them. They do have sharp teeth and an aggressive/defensive nature. Most Piranha bites are sustained when the fish are being handled, though that’s not to say a hungry fish is never dangerous.

Even when first hatched these tiny little fish have incredibly sharp teeth capable of searing anything they bite into small pieces. At first the young feed on tiny crustaceans found in the water and they also feed on fruits, seeds and aquatic plants. As they grow, so do their dietary requirements. They join schools of piranhas for the more readily available food that comes from hunting as a pack, but they also congregate in groups for protection from those that would prey on them.

Yes, Piranhas are themselves also prey! They are a favorite food for the Payara or Vampire TetraHydrolycus scomberoides, as well as other predatory fish. Herons, Caimans and other critters also prey them upon during the dry season as their pools of water are shrinking. However these fish have no social conscience and the young can become a quick snack for a more tenacious adult Piranha. This is especially true if they look like they don’t fit in with the group. Some Piranha species will practice “mimicry” when young, imitating the adults of another species just to find safe haven in their shoals until they mature enough to venture out on their own.

Also see the Red Belly Piranha profile:
Red-bellied Piranha, Pygocentrus nattereri

Piranha Species

Piranhas are native South America. They are found in Venezuela and south through Brazil inhabiting the Amazon basin and other warm lowland streams and lakes east of the Andes. In Venezuela they are also known as the Caribe.

The Piranhas belong to a sub-family called the Serrasalminae, or the ‘serrated salmon family’. This is derived from the latin terms of ‘serra’ which means ‘saw’, ‘sawed’ or ‘serrated’, and ‘salmus’ which means ‘salmon’. This name is based on the fact that all members of this subfamily have a sharp, serrated keel running over the belly to make the body more streamlined, for faster swimming.

The Serrasalminae sub-family is comprised of about 17 genera, with about sixty species. The smaller members of this sub-family are about palm-sized overall, while the largest Pacus can grow to about 3 feet and weigh about 66 pounds (30 kg). These include not only the Piranha, but also the Pacu and the Silver Dollar.

Piranha fish species are members of 5 genera:

  • Pygocentrus
    The Pygocentrus are known as the “True Piranha’s” or “Caribe”.
    (Described by J. P. Müller and Troschel in 1844)
  • Serrasalmus
    The Serrasalmus are often referred to as “Pirambeba’s”.
    (Described by Lacepède in 1803)
  • Pristobrycon
    The Pristobrycon are often referred to as “Pirambeba’s”.
    (Described by C. H. Eigenmann in 1915)
  • Pygopristis
    The Pristobrycon are often referred to as “Pirambeba’s
    (Described by G. Cuvier in 1819)
  • Catoprion
    The Catoprion genus contains the Wimple Piranha. It was not traditionally considered to be a true piranha, but though molecular analysis, it is now suggested that it is.
    (Described by G. Cuvier in 1819)

There is a lot of confusion concerning the proper scientific classification of the different species across all the genera. One reason is because of the similarity between a numbers of species and so there are frequent shifts in classification. There are also recent discoveries of a number of new species or subspecies. All this makes proper identification and classification an even more difficult enterprise.

Piranha Description

Piranha’s mostly average between 5 1/2 to 10 inches (14 – 26 cm) long, with a maximum length of up to 17 Inches (43 cm). They have deep, flattened bodies that may be silvery blue, green, brown, or black in color.

Characteristics of all Piranha fish include:

    • Body Shape
      All piranha-species have a powerful, high, thick but laterally compressed body shape, with keel-like edges running over the upper part of the body from head to dorsal fin, and on the lower body running over the belly. Together with a powerful large tail and a body covered with very small scales, their streamlined bodies make them very fast and agile swimmers.
      The oddball in the group, body shape wise is Serrasalmus elongatus, the Elongated or Pike Piranha. This species has a salmon-like, elongated and slender body, but with the same powerful, well developed tail. It is said to be the fastest swimmer of all piranha species.
      Unlike many fish-species, piranhas have a small adipose fin between tail and dorsal fin. This feature is characteristic for the Characin-family, although members from some other families, like catfish, have an adipose fin as well.

    • Eyes and Nose
      The large eyes and a large nose with big nostrils to maximize the water inflow reflect the predatory lifestyle of piranhas. They have a very acute sense of smell. In their natural habitat, the murky rivers in South-America even more darkened by overhanging vegetation; scent is their main way of tracking down their prey.

  • Teeth
    The piranha’s unmistakable trademark features are the triangular, razor sharp teeth; large ones in the lower jaw and smaller ones in the upper jaw. When the mouth is closed, the teeth from both jaws fit exactly, comparable to a bear-trap. This enables them to slice off pieces of meat or fins or scales, literally taking apart their prey piece by piece. Their teeth are replaceable, when a tooth is broken off a new one grows to replace it.
  • Visual Traits by Genus
    Beyond the basic characteristics of all Piranha fish species, there are different visual traits depending on the genera. Traits of Pygocentrus and Serrasalmus genera are:
    • Pygocentrus
      Members from the genus Pygocentrus are all recognizable by the convex shape of their head and massive bulldog-like lower jaw. It is more powerful and muscular than most Serrasalmus species.
      Besides being scavengers, if necessary all Pygocentrus species are full blown predators as well, that actively give chase to their prey.
    • Serrasalmus
      Serrasalmus piranha’s have a more concave head shape, and a less powerful lower jaw than the Pygocentrus species.
      A number of species feed themselves mainly on fins and scales of other fish, and even nuts and fruits, and therefore they do not need the same muscle packed lower jaw to rip through skin, muscle and bone. This does not apply every species of this group, however. A few, are true predators when adults, and do have very massive and powerful jaws as well.

Piranha Social Behaviors

The social behaviors of the Pygocentrus and the Serrasalmus are quite different from one another in the wild. The Pygocentrus tend to be schooling fish as while the Serrasalmus adult is very solitary. Yet the young of the Serrasalmus look identical to the adult Pygocentrus, and a juvenile will find refuge in a Pygocentrus group until it begins to mature.

Social traits of these two genera individually and in a mixed school:

  • Pygocentrus
    In the wild, piranha’s from the genus Pygocentrus live in large shoals, roaming the South American rivers. Most shoals will have one or more dominant animals, depending on the size of the shoal. These are the leader(s) of the pack. Even though the fish will often hang out together, in crucial moments the dominant fish will show its might.
  • Serrasalmus
    The behavior of the Serrasalmus genus in the wild is, due to lack of research, is largely unknown. What we know is that the Black Piranha Serrasalmus rhombeus sometimes travels and feeds in loose shoals in the wild, but prefers a solitary lifestyle. This may be due to environmental factors such as the drying up of rivers during the dry season, forcing the fish to share their constantly decreasing living space, and/or during the mating season.
    A known is the fact that juveniles from many Serrasalmus species look very different from their parents, and this has a specific reason, cannibalism. Cannibalism is very common amongst piranha’s, and the younger they are, the more species that prey on them.
  • Mixed Schools of Pygocentrus and Serrasalmus Piranhas
    Many juveniles of the Serrasalmus genus look like adult Pygocentrus piranhas. In particular is a red coloration of the lower body species like the Red Throat Piranha Serrasalmus medinai and the Sharp-Snouted Piranha Serrasalmus sanchezi. These juveniles will live in the shoals of the Pygocentrus. This behavior is called mimicry.
    Living in the middle of a shoal of larger, similar fish has certain advantages for the juveniles. Not only does a large shoal provide protection against predators, it also offers a steady supply of food to the growing up piranhas.
    Young piranha’s are also parasitic fin nippers, and will not hesitate to eat the fins of the fish in their “host” shoal to supplement their diet. When they get older, they usually leave the shoal and start living solitarily.

Piranha Diet

Piranha species are primarily carnivorous omnivores. In the wild, the staple diet of the piranha species consists of fish. They catch their prey by active chasing, or by ambushing. Besides fish, they also eat insects, crustaceans, birds that have fallen into the water, and sometimes even mammals, reptiles or amphibians. Basically anything that has attracted the attention of a hungry shoal, and is unable to leave the water in time.

Beyond using prey animals as food, these fish are very well adapted to cope with whatever circumstances their natural habitat throws at them. In times when prey animals are hard to find, piranhas will even supplement their diet with fruits, nuts and seeds.

Piranha as Predator

The splashing or erratic movements of an animal in distress attracts piranhas. Once they start feasting on their prey, other piranha’s rush to the scene. Drawn by the splashing of the victim, the blood and the noises and disturbance caused by the frenzied piranha’s that are already feasting.

Larger animals that are attacked are weakened, sick or they are injured. Even a large shoal of piranhas will only attack a healthy animal on very rare occasions. This is during the dry season, when moving around freely is as good as impossible and food is scarce.

An interesting behavior is observed with shoals of Black Spot Piranha Pygocentrus cariba. They will congregate under trees where groups of birds are nesting. Somehow, the fish know when the young birds have hatched. They patiently wait under the trees for chicks falling in the water, behavior that is remarkably similar to what Alligators do in the Everglades.

Piranha as Prey

Many piranhas fall victim to predators looking for an easy meal. Despite their fierce reputation piranhas are relatively skittish and nervous. One moment of carelessness may mean the end of your life. In the wild they are part of the diet of many predators, like jaguars, caimans, boto’s (freshwater dolphins) and other, larger predatory fish, which live there in abundance.

Piranhas are even preyed upon by their own relatives, especially among the young and during the dry season. This is when the amount of food is increasingly limited and the fish are frequently trapped in increasingly small puddles. Juvenile piranha’s have to face even more natural predators, and are even targeted by large insects and crustaceans.

A group of Pygocentrus piranha’s lives in a state of constant fear and mutual mistrust, even when all seems calm: the animals are all capable of severely wounding or even killing each other. To survive, the fish must always know where the others are, in what their states of mind they are, and how they might act the next moment. Letting your guard down may turn out fatal.

Cannibalism amongst piranhas is not unusual during the dry period, especially among the young. And perhaps also during the mating season, when aggression levels are at their highest. By weeding out the weaker animals, piranha’s have the same task as the vultures or hyena’s of the savannah. They are the health police of their habitat.

Piranha Fish Aquarium

The Pygocentrus and Serrasalmus genera contain the species that most piranha owners keep. Most captive piranhas are less skittish and shy when they live in a tank with enough places to hide and dimmed lights. It makes them feel more at ease and secure, which will be reflected in their behavior. The fish will be more active, swim around more freely, and behaving in a more ‘natural’ way.

Pygocentrus species live in large schools in the wild and this situation is impossible to imitate in captivity. But even in a tank they will show some traits of their wild behavior, provided they are kept under proper conditions. In most cases, the alpha-animal will be the largest, most aggressive and bold specimen. It will be first at feeding sessions. It will own and guard the best spots in the tank, like the spot with the best view and the best place during feeding time, or in the current from a powerhead. Any unwilling ‘servants’ will be corrected instantly by aggressive behavior, chasing or even inflicting wounds.

Piranha’s from the genus Serrasalmus are solitary fish, with the exception of a few species like the Gold Piranha or Gold Spilopleura Serrasalmus spilopleura, Ruby Red Piranha Serrasalmus maculatus, and Violet Line Piranha
Serrasalmus geryi. In general, they will not tolerate other fish in their tank, and are very aggressive and territorial.

Piranha Sexual differences

Determining the gender of piranhas is considered almost or all together impossible by most piranha experts. There are no visible differences between the genders, in other words piranhas are not sexually dimorphic.

The general consensus is that the only more or less foolproof method to sex piranha’s is to observe them during spawning. It is true that adult female specimens tend to be thicker due to the eggs they carry. Nonetheless that is an unreliable method to tell both genders apart, as well-fed males are often just as thick.

The only known exceptions to this sexual dimorphism are possibly the Five-Cusped Piranha Pygopristis denticulate, and the Wimpel Piranha Catoprion mento. For the Wimpel Piranha, males and females are easy to tell apart.

Piranha Breeding

The first challenge to breeding piranhas is finding a suitable breeding pair. Sexing is unreliable, although the thickness of the fish has been suggested to indicate gender. Frequent, large water changes should induce breeding, as these fish believe the rainy season has begun.

The fish will dig a pit and will then spawn. Do not disturb them during spawning. After the eggs have been deposited, the female will then swim away and the male will guard the nest. The eggs should be raised in a separate tank and the fry should be given baby brine shrimp once they are free swimming. It should be noted that breeding this fish is difficult and an optimal process for doing so is not well established.


Featured Photo © Animal-World: Courtesy Jonas Hansel