Sources do not describe what the red-bellied piranha eats in one way. A genome paper calls the species mostly a carnivorous piscivore, a fish eater, that can be opportunistic and feed on plants, insects, worms and crustaceans. Biologist Steve Huskey of Western Kentucky University says piranhas get the vast majority of their nutrients by clipping the fins of other fish. Other sources add snails and other mollusks, carrion, plants and fruit. In the wild, a good portion of the food is fins nipped from the tails of larger fish, and the fish mostly ambush other fish from within the aquatic vegetation and dash after passing prey. Some piranha relatives are completely vegetarian.

Piranhas swim in large shoals as a defence against their many predators, including dolphins, larger fish and birds. A 2005 study concluded that shoaling has a cover-seeking function in this species. A science writer reporting on piranha experiments says that piranhas in larger shoals are far less stressed than those alone or in small shoals. In a shoal, the younger piranhas are often toward the outside of the group and the larger, sexually mature adults are in the center. A shoal can have more than a hundred fish in it. You may have heard that piranhas hunt in packs. In fact, they gather in groups for protection rather than hunting their prey in packs.

The red-bellied piranha is a fish that lives in rivers in South America. It has a red belly and a gray body flecked with silver. Adult piranhas vary in color pattern and body size with geographic location. It likes warm water, about 25 degrees Celsius. It lives in the Amazon River basin. It is often found in whitewater streams in South America and often not in blackwater streams. FishBase says it is common in creeks and interconnected ponds in Matto Grosso, Brazil. The National Zoo says it is relatively common throughout its range, as of November 2026.

Male piranhas build nests in the mud and sand at the bottom of the water. Spawning seems to occur during the wet season, and a courtship starts with swimming around in circles. Eggs and spawn are deposited in several batches and guarded by the male, sometimes assisted by the female. The eggs are laid in clusters and stuck to plants growing under the water, and a female can lay thousands of eggs. A red-bellied piranha can live about 10 years. Another kind of piranha, Serrasalmus marginatus, has been seen taking crustacean parasites off the bodies of red-bellied piranhas. FishBase lists a highly evolved capacity for hearing, and they make sounds using muscles attached to the swim bladder.

Words to know

• genome: all its genes
• piscivore: fish eater
• shoaling: group swimming
• parasites: tiny freeloaders
• spawn: fish eggs