Piranhas are social creatures, often found in schools that can range from a few individuals to hundreds. This schooling behavior is primarily a defensive mechanism against predators, as there is safety in numbers. During the dry season, when water levels drop and food becomes scarce, piranhas can become more aggressive and opportunistic in their feeding habits. However, their reputation as ferocious predators is largely unfounded, as attacks on humans are extremely rare and typically occur only when the fish are stressed or provoked.

Physically, piranhas are characterized by their deep, laterally compressed bodies, which allow them to navigate through the dense vegetation of their riverine habitats. Their distinctive red bellies, which are most pronounced in the red-bellied piranha, serve as a warning to potential predators and rivals. These fish possess a formidable set of triangular teeth that interlock, enabling them to slice through flesh with ease. This dental structure is not only effective for feeding but also for defending themselves from threats. The piranha's role in indigenous cultures is varied, with some communities viewing them as symbols of strength and others as omens of danger. In addition to their ecological importance, piranhas have become a subject of fascination and study, contributing to our understanding of aquatic life and predator-prey dynamics.