Red-bellied Piranha

The red-bellied piranha is a freshwater fish of South America, found in the Amazon, Paraguay, Paraná and Essequibo basins and in coastal rivers of northeastern Brazil, where it is locally abundant. Adults have a reddish belly, while juveniles are silver with darker spots. It can reach 50 cm and 3.9 kg but rarely surpasses 35 cm. Despite its ferocious reputation it is primarily a scavenger and an omnivore, eating insects, worms, crustaceans, fish, aquatic plants, fruits, nuts and seeds. It travels in shoals as a defence against predators but rarely hunts as a group, and it communicates with sounds, sometimes alongside aggressive behaviour.

About the red-bellied piranha

The red-bellied piranha (Pygocentrus nattereri), also called the red piranha, is a freshwater ray-finned fish of South America in the family Serrasalmidae, which also includes the pacus. It lives in the Amazon, Paraguay, Paraná and Essequibo river basins, and despite its fierce reputation it is mainly an omnivorous scavenger and forager.

The species is named after Johann Natterer. Members of its family have deep bodies flattened from side to side and long dorsal fins. The genus Pygocentrus is set apart by its unusual teeth and the width of its head. Red-bellied piranhas cover a larger geographic area than any other piranha species.

Adults are gray to silver-gray on the back and sides, with silver-flecked scales, and reddish-orange on the belly, which gives the fish its name. Females have a slightly deeper red belly than males. The pectoral and pelvic fins range from red to orange, the dorsal fin is black, and the anal fin is usually black at the base. Some fish have blackish spots behind the gills.

Juveniles are silver with darker spots. As they grow, the number of body spots increases and a black line in the anal fin fades. Color and body size also vary by region. Most adults stay under 35 cm (14 in) long, though the species can reach 50 cm (20 in) in standard length and 3.9 kg (8 lb 10 oz).

Behavior and diet

The red-bellied piranha eats a broad mix of foods: fruit, leaves, seeds, nuts, insects, worms, crustaceans, snails, carrion and fish, including fins and scales bitten from other fish. In the rainy season, when food is plentiful, it eats mainly plants and insects. In the wild it tends to target weak, injured, dying or dead animals. It is described as a timid scavenger that fills a role similar to vultures on land.

Feeding habits change with size. Small fish of 80–110 mm (3–4 in) forage during the day, while larger fish of 150–240 mm (6–9 in) feed at dawn, in the late afternoon and early evening, a crepuscular pattern. Groups of 20 to 30 wait in vegetation and ambush prey that swims past, or chase it down after lying in wait.

Piranhas swim in shoals, but studies have found no evidence that they hunt as a pack. Shoaling instead protects them from predators such as dolphins, large predatory fish, caimans, and birds such as storks, herons and anhingas. In experiments, piranhas in shoals of eight calmed down faster after a simulated attack than those in shoals of two. Rare feeding frenzies, in which a shoal strips a large animal within minutes, are usually linked to provocation or starvation. Packs of hundreds have been known to feed on animals as large as egrets or capybaras.

Piranhas also make sounds, produced by fast contractions of muscles attached to the swim bladder. Researchers have identified three call types. A harmonic sound of about 140 milliseconds goes with face-to-face displays, a short 36-millisecond sound with circling and fighting over food, and a single 3-millisecond pulse with chasing and biting.

The fish breed during the rainy season. Pairs dig bowl-shaped nests about 4–5 cm (1.5–2 in) deep and 15 cm (6 in) across among water grasses, and females lay several thousand eggs, around 5,000, which stick to the plants. Adults circle the nest to guard it. The eggs hatch in two to three days, and the young hide in plants until they are big enough to defend themselves.

Range and habitat

Red-bellied piranhas live east of the Andes in Argentina, Brazil, Bolivia, Colombia, Ecuador, Guyana, Suriname, Paraguay, Peru, Uruguay and Venezuela. They occur in the Amazon, Paraguay, Paraná and Essequibo basins, in coastal rivers of northeastern Brazil and in many smaller river systems.

They are mainly whitewater fish but have also been recorded in blackwater and clearwater. They live in large rivers, streams, oxbow lakes, reservoirs behind dams, floodplains and flooded forests. They tolerate water from 15 to 35 °C (59 to 95 °F) and can survive 10 °C (50 °F) for a time.

Outside South America, the species was introduced to China, probably through the aquarium trade, and has been invasive there since it was first detected in 1990. The species is not found in the United States. A single fish was found in 1998 in a golf course lake in Simi Valley, California, and California and Washington prohibit the species and encourage surveillance to keep it out.

Red-bellied piranha: myth vs reality

Much of the piranha's fearsome image traces to Theodore Roosevelt, who returned from the Roosevelt-Rondon expedition with a story of piranhas stripping a cow to the bone in minutes. Local guides had staged the event, penning starved fish in a section of river for over a week before driving the cow in. Films such as Piranha (1978) reinforced the myth.

Conservation status

The red-bellied piranha is listed as Least Concern on the IUCN Red List. It is widespread and locally abundant, and in some parts of its range it is among the most common fish. Collection for the aquarium trade may pose a low local risk. Where it has been introduced outside its native range, it usually harms the local fish fauna.