Piranha Social Behaviors
The social behaviors of the Pygocentrus and the Serrasalmus are quite different from one another in the wild. ThePygocentrus tend to be schooling fish as while the Serrasalmus adult is very solitary. Yet the young of theSerrasalmus 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 PiranhaSerrasalmus 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 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.
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.
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