Introduction Species Body characteristics
Social behavior Reproduction


The piranha's are members of the Characidae (or Characin) family, a large family of more than 1200 species, including some of the most widespread and popular aquarium fish like the all the common tetra's and hatchetfish. The piranha's belong to a sub-family called the Serrasalmidae (serra means 'saw', 'sawed' or 'serrated', salmus means 'salmon'), a name based on the fact that all members have a sharp, serrated keel running over the belly to make the body more streamlined (for faster swimming). How many members this subfamily consists of is not certain because there is a lot of debate over the proper scientific classification. Besides that, new unidentified species, regional varieties and color forms are discovered, and new and/or updated research data (concerning DNA, parasites, morphology etc.) is published on a fairly regular basis. For what is known, there are at least more than 40 different species (Silver Dollars, Pacu's, Whimple Piranha's etc. included).

The subfamily of Serrasalmidae is divided in separate genera: Pygocentrus, Serrasalmus, Pristobrycon, Pygopristis, Catoprion, Metynnis, Colossoma and a few more. The species belonging to the first family are also known as "True Piranha's", members from the genus Serrasalmus are often referred to as "Pirambeba's". These two are the groups I will discuss mainly here, since most piranha owners keep species from these two genera. Like stated above, there is a lot of confusion concerning the proper scientific classification of the different species of the Pygocentrus and Serrasalmus genera, because of the similarity between a number of species and the frequent shifts in classification: for example, in the past Pygocentrus nattereri (the well-known Redbellied Piranha) was classified as Serrasalmus nattereri and Rooseveltiella nattereri, Pygocentrus cariba as Serrasalmus notatus, and Serrasalmus rhombeus as Serrasalmus niger. And there are many similar cases.
The recent discovery of a number of new species or subspecies makes proper identification and classification an even more difficult enterprise. For example, the species formerly known as Serrasalmus niger is nowadays known as Serrasalmus rhombeus, and there are many indications that this species is in actuality a complex of similar looking, but different fish (depending on the collection point, among other factors), which means the Serrasalmus rhombeus-'complex' eventually may be split up in separate species if scientific research confirms this theory. The same applies to Serrasalmus spilopleura: this species may actually be a complex of similar species with subtle differences in shape, color and locality (for example, in the pet trade, some specimen are sold as Gold Spilopleura, others as Purple Spilopleura, obviously because of their coloration).

Serrasalminae Classification (per Nelson, 1994)
Phylum: CORDATA (animals with brains)
Subphylum: VERTEBRATA (animals with backbones)
Superclass: GNATHOSTOMATA (jawed vertebrates)
Class: ACTINOPTERYGII (ray-finned fishes)
Division: TELEOSTEI (true bony fishes)
Super order: OSTARIOPHYSI (bony fishes)
Order: CHARACIFORMES (characin forms)
Family: CHARACIDAE (characins)
Subfamily: SERRASALMIDAE ('serrated salmon' family)
  • PYGOCENTRUS: Caribe / 'True' Piranha's
  • SERRASALMUS: Pirambeba's
  • PRISTOBRYON: Pirambeba's
  • PYGOPRISTIS: Pirambeba's
  • CATPRION: Wimpel Piranha's
  • COLOSSOMA: Tambaqui / Pacu's
  • ACNODON: Sheep Pacu's
  • OSSUBTUS: Parrot Pacu's
  • METYNNIS: Silver Dollars
  • MYLEUS: Silver Dollars
  • MYLOSSOMA: Silver Dollars

top Go to top of page

Piranha species

(names taken from


Pygocentrus cariba: Cariba Piranha, Cariba, Caribe, Black Shoulder Piranha, Orinoco Piranha, Black Eared Piranha, Venuzuelan Red Belly Piranha
Pygocentrus nattereri: Redbellied Piranha, Red Bellied Piranha, Redbelly Piranha, Red, Red Breasted Piranha, Red Piranha, Piranha, Common Piranha, Pygocentrus nattereri 'Ternetzi', Ternetzi Piranha, Yellow King Emperor Piranha, Gold Dust Piranha, Yellow Nattereri, Golden Redbellied Piranha, Yellow Redbellied Piranha
Pygocentrus piraya: Piraya, Piraya Piranha, Black-Tailed Piranha, Rio São Francisco Piranha, King Emperor Piranha


Serrasalmus altispinis: ???
Serrasalmus altuvei: Altuvei Piranha, "Caribe Azul"
Serrasalmus brandtii: Brandtii Piranha, Green Piranha, "Cavaca"
Serrasalmus compressus: Compressus Piranha
Serrasalmus eigenmanni: Eigenmann's Piranha
Serrasalmus elongatus: Elongated Piranha, Pike Piranha, Pingke Piranha, Serrasalmus pinke, "Caribe Pinche"
Serrasalmus geryi: Geryi's Piranha, Violet Line Piranha
Serrasalmus gibbus: Gibbus Piranha, Castelnau's Piranha, "Caribe Dorado"
Serrasalmus gouldingi: Goulding's Piranha
Serrasalmus hastatus: ???
Serrasalmus hollandi: Holland's Piranha
Serrasalmus humeralis: Humeralis Piranha,
Serrasalmus irritans: Iredescent Piranha, "Caribe Pinche"
Serrasalmus maculatus: Maculatus Piranha, Mac
Serrasalmus manueli: Manuel's Piranha, Green Tiger Piranha, "Caribe Parguasero"
Serrasalmus marginatus: "Caribe"
Serrasalmus medinai: Medinai Piranha, Red Throat Piranha, "Caribe"
Serrasalmus nalseni: "Caribe Pintado"
Serrasalmus neveriensis: Rio Neveri Piranha, "Caribe de Rio"
Serrasalmus rhombeus: Rhombeus Piranha, Rhom, Black Piranha, White Piranha, Peruvian Black Piranha, Brazilian Black Piranha, Spotted Piranha, S. Niger Piranha, "Caribe Amarillo", "Caribe Ojo Rojo"
Serrasalmus sanchezi: Ruby-Red Piranha, Ruby-Throated Diamond Piranha
Serrasalmus serrulatus: "Caribe Cortador"
Serrasalmus spilopleura: Spilopleura Piranha, Spilo, Gold Piranha, Gold Spilopleura, Ruby Red Piranha, Purple Spilopleura, Black Piranha, Black Diamond Piranha, Speckled Piranha, Black-Banded Piranha, "Caribe Dorado"


Pristobrycon aureus: Gold Piranha, "Palometa", "Palometa de Rio", Yellow Palometa
Pristobrycon calmoni: Dusky Piranha
Pristobrycon careospinus: ???
Pristobrycon maculipinnis: Gemarmerde Piranha
Pristobrycon striolatus: Spotted Piranha, Scapularis Piranha, "Caribito", "Palometa Caribe"


Pygopristis denticulata: Five-Cusped Piranha, Denticulata Piranha, Big-Toothed Piranha, Gold Piranha, "Caribe Palometa", "Caribito"

GENUS CATOPRION (Wimpel Piranha's)

Catoprion mento: Wimpel Piranha


Colossoma bidens: Black Pacu, Silver Pacu
Colossoma brachypomus: Pacu, Common Pacu, Red Pacu
Colossoma macropomum: ???
Colossoma oculus: ???
Colossoma orbignyanum: ???

Acnodon normani: Sheep Pacu
Acnodon oligacanthus: ???

Ossubtus xinguensi: Parrot Pacu


Metynnis altidorsalis: ???
Metynnis argenteus: Silver Dollar
Metynnis fasciatus: Striped Silver Dollar
Metynnis guaporensis: ???
Metynnis hypsauchen: Schreitmüller's Silver Dollar, Striped Silver Dollar
Metynnis lippincottianus: Spotted Silver Dollar
Metynnis luna: Red-Spot Silver Dollar
Metynnis maculatus: Speckled Silver Dollar
Metynnis mola: ???
Metynnis otuquensis: ???

Myleus rubripinnis: Red Hook Silver Dollar
Myleus schomburgki: Black-Barred Silver Dollar

Mylossoma duriventre: Silver Mylossoma, Hard-Bellied Silver Dollar

top Go to top of page

Body characteristics

Piranha anatomy

Piranha anatomy
Special thanks to Frank Magallanes (OPEFE) for helping me out with this image

As mentioned, piranha's can be divided into a number of different genera, all with different visual traits. Members from the genus Pygocentrus are all recognizable by the convex shape of their head and massive bulldog-like lower jaw (more powerful and muscular than most Serrasalmus-species). This reflects their diet: besides being scavengers, if necessary all Pygocentrus-species are full blown predators as well, that actively give chase to their prey.
Serrasalmus-piranha's have a more concave head shape, and less powerful lower jaws. 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: Serrasalmus rhombeus, manueli and elongatus, to name a few, are true predators when adult, and do have very massive and powerful jaws as well. But regardless of their diet, all Serrasalmus-species share the piranha's unmistakable trademark feature, 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.

Convex head, typical for the Pygocentrus group Concave head, typical for the Serrasalmus group
Convex headshape, typical for the Pygocentrus group Concave headshape, typical for the Serrasalmus group

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 large and 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 family, 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, piranha's 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.
Their predatory lifestyle is reflected by large eyes and a large nose with big nostrils to maximize the water inflow. They have a very acute sense of smell: in their natural habitat, murky rivers in South-America, even more darkened by overhanging vegetation, scent is their main way of tracking down their prey.

Determining the gender of piranha's is considered almost or all together impossible by most piranha experts, because there are no visible differences between the genders (in other words, piranha's are not sexually dimorphic). The general consensus is that the only more or less fool-proof method to sex piranha's is to observe them during spawning. It is true that adult female specimen tend to be thicker due to the eggs they carry, it nonetheless 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 the Wimpel Piranha (Catoprion mento), of which males and females are easy to tell apart, and possibly the Five-Cusped Piranha (Pygopristis denticulata).

top Go to top of page

Social behavior

In the wild, piranha's from the genus Pygocentrus live in large shoals, roaming the South American rivers. 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.
First of all, most shoals will have one or more dominant animals, depending on the size of the shoal: 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. In most cases, the alpha-animal will be the largest, most aggressive and bold specimen, first at feeding sessions and owning and guarding the best spots in the tank (the spot with the best view, the best place during feeding time, in the current from a powerhead). Any unwilling 'servants' will be corrected instantly by aggressive behavior, chasing or even inflicting wounds.
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.
This behavior may be a partial explanation why many captive pirana's are relatively skittish and nervous, despite their fiercesome reputation. One moment of carelessness may mean the end of your life, even more in the wild, where piranha's 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. And piranha's are even preyed upon by their own relatives, especially amongst the young and during the dry season, 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. Most captive piranha's 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.
In the wild, the staple diet of the carnivorous Pygocentrus 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. It is observed that shoals of Pygocentrus cariba 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. And in times when prey animals are hard to find, piranha's will even supplement their diet with fruits, nuts and seeds when prey animals are hard to find, highlighting that these fish are very well adapted to cope with whatever circumstances their natural habitat throws at them.
Most larger animals that are attacked, are weakened, sick or injured: even a large shoal of piranha's will only attack a healthy animal on very rare occasions: during the dry season, when moving around freely is as good as impossible and food is scarce. Cannibalism amongst piranha's is not unusual during this period, and many others fall victim to predators looking for an easy meal. 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's are attracted by splashing or the erratic movement of an animal in distress. 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.

With the exception of a few species (like Serrasalmus spilopleura, Serrasalmus maculatus en Serrasalmus geryi), piranha's from the genus Serrasalmus are solitary fish. In general, they will not tolerate other fish in their tank, and are very aggressive and territorial. Their behavior in the wild is, due to lack of research, largely unknown. What we know is that Serrasalmus rhombeus sometimes travels and feeds in loose shoals in the wild, but prefer 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.
Also known is the fact that juveniles from many Serrasalmus-species look very different from their parents, and this has a specific reason: cannibalism is very common amongst piranha's, and the younger they are, the more species prey on them. Many juveniles look like adult Pygocentrus piranha's (in particular: a red coloration of the lower body, ie. Serrasalmus medinai en Serrasalmus sanchezi), and live in their shoals. 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 piranha's. 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.

top Go to top of page


Not a whole lot is known about piranha reproduction, as observations made in the wild are few in numbers. Almost everything we know about reproduction is based on observations made in aquariums, and only of a few species that so far have successfully reproduced in captivity. Pygocentrus nattereri (including the "Ternetzi" variant), Serrasalmus maculatus and Serrasalmus spilopleura, and more recently (2002) Pygocentrus cariba, have reproduced in home aquariums. Additionally, some other species, like Serrasalmus rhombeus, have been observed to reproduce in large public aquariums and zoo's.
The description below is based on the breeding of Pygocentrus nattereri, the species that has been bred most extensively in captivity. But this can also be applied to the other Pygocentrus species, and perhaps to other species as well, although Serrasalmus courtship and spawning might differ, since most of the species are living solitarily and are very aggressive, even towards their own species. It is suspected that (certain?) Serrasalmus species release a certain kind of hormone into the water, thus signaling that the fish is ready to spawn and thus lowering aggression levels.
To trigger breeding, all circumstances must be right. First of all, the tank must be in a quiet environment. Besides that, the fish must be compatible (that means: a group that has been together for a long time, with a developed social hierarchy). Furthermore, the water quality must be perfect (zero ammonia and nitrates, excellent pH and a temperature of about 82 degrees), and the tank must be large enough for the fish to be able to pair off and form a territory of their own, without too much disturbance. And last but not least you just need a large dose of good luck...

When a pair is ready to spawn, they form a little territory from which other fish are aggressively chased away. Both fish become much darker in color, and their behavior becomes more territorial and aggressive. In their territory, the fish start to build a nest by on the bottom, by clearing all plants and removing stones etc. with their tails and by blowing it away. When the nest is ready, the male tries to lure the female over the nest. Here she will lay here eggs, which will be fertilized quickly by the male. After the spawning, the male guards the nest, and chases off every fish that comes too close. Sometimes the female will be expelled, but sometimes she helps with the guarding.
The orange-colored, fertilized eggs will hatch in 2-3 days. The fry's yoke sack provides nutrients the first couple of day. A few days later they will start swimming around freely. This may be the best moment to remove the fry, to raise it in a breeder tank. At this moment, the parents may still aggressively guard their offspring, so be careful when syphoning off the fry.

A Red Piranha's life in a nutshell
Fertilized Redbellied Piranha eggs Redbellied Piranha fry (1 week old)
Fertilized Redbellied Piranha eggs Redbellied Piranha fry (1 week old)
Juvenile Redbellied Piranha's (1 month old) Sexually mature Redbellied Piranha (4,5 years old)
Juvenile Redbellied Piranha's (1 month old) Sexually mature Redbellied Piranha (4,5 years old)

Young Redbellied Piranha's are silver in color, their body covered with small black spots. The shape of the head is much more concave than adults and they have very large eyes. Juvenile Pygocentrus piranha's can be pretty hard to tell apart from baby Serrasalmus species, because they very much look the same, making proper identification a difficult task.
Even at young age, piranha's are very greedy eaters. They should be fed newly hatched brine shrimp the first days, and their diet can be complemented with flakes, blood worms, mosquito larvae and other small foods when older. And they should be fed often, at least 2-3 times per day, to keep them healthy and properly developing. Juveniles grow fast: in their first months the growth speed can increase to half an inch to an inch per month, and soon their diet can be complemented with small feeders (I used Neon Tetras), pieces of fish, shrimp etc. Beef heart should not be fed until the young fish have reached an age of at least 9 months, because of their high contents of fat and fibres. This puts a lot of strain on their not yet fully developed digestive system, and constipation may eventually turn out fatal for the young fish. The same is true for adult piranha's as well, although an occasional treat of beef heart (once per month) is unlikely to cause any problems.
In a few months, they start to develop red coloration in their fins and belly, the black spots start to fade, and the silvery color of their body is gradually replaced by the more (bluish or greenish) steel grey which is so characteristic for adult specimen. The growth rate remains high until the fish reach a length of about 4-6 inches: by then, the fish are about 12 to 14 months old, depending on the circumstances they live in: tank space, diet, water quality, the stress factor, the presence of water current from a powerhead. After that, a Red Bellied Piranha's growth slows down to about 1" per year (and even less once they hit the 9-10" marker) and reach sexual maturity when then are between 18 and 24 months old, once again depending on the factors mentioned above. The older the fish, the darker it will get. Some specimen will almost completely loose their red belly and turn completely pitch black (see picture above), sometimes because of old age, sometimes because of stress, and sometimes to signal they are ready to spawn.

Redbellied Piranha development
Ed, about two months after I bought him The same fish, 6 months later The same fish, another 6 months later
Over the course of 12 months, Red Bellied Piranha's undergo an impressive transformation, size- and colorwise.
After approximately 18-24 months they are sexually mature. In all pictures you see the same fish

Valid XHTML Strict 1.0