Red-Bellied Piranha (Pygocentrus nattereri): Facts and Bite

What does a red-bellied piranha look like?

The red-bellied piranha has a deep, flattened body, a blunt head and a heavy lower jaw that juts forward past the upper jaw. Adults are silvery gray to olive on the back and sides, often with glittering, silver-flecked scales. The throat, belly and lower fins are orange to bright red, which gives the species its name. The anal fin is usually black at the base, and a dark shoulder spot may show behind the gills.

Young piranhas look quite different. They are silvery with many small dark spots, and the red belly only develops as they grow. Color varies between river systems and with breeding condition, and some breeding adults turn darker overall. Males and females look alike, although females are sometimes slightly redder on the belly.

The species is named after Johann Natterer, an Austrian naturalist who collected animals in Brazil in the early 19th century. In Brazil and other countries it is often known simply as piranha, or as piranha-caju or red piranha.

How big do red-bellied piranhas get?

Most adult red-bellied piranhas are 20–35 cm (8–14 in) long. The largest recorded fish reached about 50 cm (20 in) in standard length, which excludes the tail fin, and about 3.9 kg (8.6 lb), but such giants are rare. Fish mature at about 15 cm (6 in), often around one year old.

Teeth and bite

The piranha’s teeth are its most famous feature. Each jaw holds a single row of flat, triangular teeth with sharp points and edges. Small cusps lock neighboring teeth together, so the whole row works like one serrated blade. When the jaws close, upper and lower teeth slice past each other like scissors, letting the fish cut a neat, crescent-shaped bite out of prey.

Piranhas lose and regrow their teeth throughout life. Instead of replacing teeth one at a time, they replace them in sets, on alternating sides of the jaws, so one side always has working teeth while the other side regrows.

Short, powerful jaw muscles attached close to the tip of the jaw give piranhas an unusually strong bite for their size. The record among bony fish belongs to a relative, the black piranha (Serrasalmus rhombeus), which was measured biting with more than 320 newtons, roughly 30 times its own body weight. You can compare it with other champions in our list of the strongest bite forces.

Where do red-bellied piranhas live?

Red-bellied piranhas live east of the Andes in the Amazon basin, the Paraguay–Paraná basin, the Essequibo basin in Guyana and coastal rivers of northeastern Brazil. Their range includes parts of Argentina, Bolivia, Brazil, Colombia, Ecuador, Guyana, Paraguay, Peru, Uruguay and Venezuela. The Pantanal wetlands of Brazil, Bolivia and Paraguay are one of the best places to see them.

They are found mainly in whitewater rivers, which carry muddy, nutrient-rich water from the Andes, but also live in clearwater and blackwater habitats. They use main rivers, streams, oxbow and floodplain lakes, flooded forests and reservoirs behind dams. During the rainy season they spread into newly flooded land, and in the dry season many become trapped in shrinking lakes and pools.

Outside South America, the red-bellied piranha is a popular aquarium fish. Released fish are occasionally caught in North America and elsewhere, but there are no known established wild populations in the United States.

What do red-bellied piranhas eat?

The red-bellied piranha is an omnivore and an opportunist. It eats whole fish and pieces of fish, fins and scales bitten from living fish, insects, worms, crustaceans and snails, and carrion such as dead fish and animals. It also takes seeds, fruit, leaves and other plant matter, especially in the rainy season when the forest floods.

Young piranhas forage mainly by day and eat many small crustaceans and insects, and they often nip fins and scales from other fish. Larger fish feed mostly at dawn, in the late afternoon and early in the night. They often lurk among water plants and dash out at passing prey, but they also chase prey and scavenge. For a closer look at the menu and how it changes with age and season, see What do piranhas eat?

Shoaling, sounds and behavior

Red-bellied piranhas usually live in shoals, often of about 20–30 fish, and larger groups gather where food is plentiful or water is low. For a long time these shoals were thought to be hunting packs. Field and aquarium studies tell a different story: the fish gather mainly for safety. In one experiment, piranhas kept in groups of eight calmed down faster after a simulated predator attack than fish kept in pairs, as shown by their breathing rate.

Within a shoal, piranhas form a pecking order, and larger fish often get the first bites at food. Disputes are common and fins are frequently nipped, but injured fins regrow quickly.

Piranhas are also surprisingly noisy. Using special muscles that vibrate the swim bladder, they make low bark-like sounds during face-offs, drumming sounds while circling each other in fights over food, and short snapping sounds when chasing or biting another piranha. Most of these sounds are heard during social encounters rather than hunting.

Reproduction and nest guarding

Red-bellied piranhas breed during the rainy season, when rising water floods grassy margins and vegetation. Breeding pairs choose a site among submerged plants, often in lakes and backwaters, and clear a shallow, bowl-shaped nest about 4–5 cm (1.5–2 in) deep and around 15 cm (6 in) across.

The female lays several thousand sticky eggs, which cling to plant stems and roots in and around the nest, and the male fertilizes them. Adults then stay near the nest, swimming in tight circles around it and driving away egg-eating fish. This nest guarding is a real form of parental care. After hatching, the tiny young hide among the vegetation and feed on zooplankton until they are large enough to eat insects and small fish.

Piranha relatives and look-alikes

The red-bellied piranha belongs to the family Serrasalmidae, which also includes the pacus and the silver dollars. Scientists disagree about how many piranha species exist, and estimates range from fewer than 30 to more than 60. The genus Pygocentrus has three species: the red-bellied piranha, Pygocentrus cariba of the Orinoco basin in Venezuela and Colombia, and the São Francisco piranha (Pygocentrus piraya) of eastern Brazil.

Pacus look much like piranhas but have blunt, rounded teeth for crushing seeds, nuts and fruit. In North America, a red-bellied pacu released from an aquarium is often mistaken for a red-bellied piranha, which explains many “piranha” reports in lakes and rivers. Piranhas also have a giant fossil relative, Megapiranha paranensis, which lived in Argentina about 8–10 million years ago and is thought to have reached roughly 70 cm (28 in) in length.

Lifespan, predators and conservation

Little is known about how long red-bellied piranhas live in the wild. In captivity they commonly live about 10 years, and some live longer.

Despite their teeth, piranhas are prey for many animals. Their predators include caimans, river dolphins, giant otters, large predatory fish and birds such as cormorants, herons, storks and anhingas. People also catch them for food in many parts of South America.

The red-bellied piranha is listed as Least Concern on the IUCN Red List. It is widespread and locally abundant, and in some areas it is among the most common fish. Collection for the aquarium trade is considered a low risk to the species, and some piranhas do well in the reservoirs created by dams.

Are red-bellied piranhas dangerous? Myths and facts

Piranhas owe much of their fearsome image to former US president Theodore Roosevelt. During his 1913–1914 expedition in Brazil he heard dramatic piranha stories, including one of a cow stripped to the bone within minutes, and in his book Through the Brazilian Wilderness he described piranhas as the most ferocious fish in the world. According to later accounts, the famous cow scene was staged: local fishers had blocked off a stretch of river and left the fish without food for days before driving the animal into the water.

In reality, attacks on people are uncommon and usually consist of a single bite to a foot or hand, often in crowded dry-season pools, near fishing activity or close to nests. Deaths are very rare, and in several reported cases the person had already drowned. Read more in Are piranhas dangerous?

Piranhas and people

For people living along South American rivers, piranhas are mainly a food fish, eaten fried or in soups and sold at local markets. Fishers often see them as a nuisance because they steal bait, damage nets and bite through lines. Several Indigenous peoples have used piranha teeth and jaws as cutting tools.

The word “piranha” comes from the Tupi language of Brazil and was recorded in the 16th century with the meaning “scissors”. Red-bellied piranhas share these rivers with other famous South American animals, including the capybara, the world’s largest rodent.