Piranha

The red-bellied piranha is a deep-bodied freshwater fish native to river basins across South America, including the Amazon, Orinoco, and Paraguay-Parana systems. It belongs to the family Serrasalmidae and is one of the best-known piranha species due to its striking silver-and-orange coloration and powerful, interlocking triangular teeth. Despite a popular reputation for aggression, red-bellied piranhas are primarily opportunistic scavengers and school for protection against their own predators, particularly as juveniles, rather than purely for coordinated hunting. They play a notable ecological role as scavengers and predators within Amazonian floodplain and river food webs.

• Deep, laterally compressed, disc-shaped body
• Silvery flanks with fine dark speckling
• Bright red-orange belly and lower fins, especially vivid in adults
• Blunt head with a strongly protruding lower jaw
• Sharp, triangular, interlocking teeth visible when the mouth is closed
• Small adipose fin near the tail, typical of characiform fish
• Adults typically 20-33 cm

Distinguished from similarly shaped pacu (herbivorous relatives) by its sharper, more triangular teeth and pointed jaw versus the pacu's blunter, molar-like teeth. Coloration intensifies with age, with juveniles showing a more silvery body and darker spotting that gradually gives way to the deep red-orange belly seen in mature adults.

Red-bellied piranhas inhabit slow-moving rivers, floodplain lakes, and flooded forest margins throughout the Amazon and other major South American river basins. They favor warm water generally between 24-30 degrees C, with abundant submerged vegetation and structure offering cover. Populations shift seasonally with flood cycles, moving into flooded forest habitat during high water and concentrating in permanent channels and lakes during the dry season when water levels drop and prey becomes more concentrated. They tolerate a range of turbidity and prefer slower currents over fast-flowing stretches.

Piranhas form loose schools, particularly as juveniles, which appears to function mainly as protection from larger predatory fish rather than for coordinated group hunting. They are opportunistic feeders taking fish, insects, crustaceans, and carrion, with feeding activity often intensifying during the dry season when prey is concentrated in shrinking pools. Spawning occurs during the rainy season, when pairs deposit adhesive eggs among submerged vegetation that both parents may guard briefly. As both predators and scavengers, piranhas help regulate fish populations and recycle nutrients from carcasses within Amazonian aquatic ecosystems.