Pacu

The Pacu, also known as the Red-bellied Pacu, is a large, deep-bodied characin native to the Amazon and Orinoco river basins of South America, closely related to piranhas but almost entirely herbivorous as an adult. The body is round and laterally compressed, similar in outline to a Silver Dollar but growing to dramatically larger size, with a robust, muscular build. Coloration is silvery-gray dorsally, transitioning to a distinctive reddish-orange wash across the belly and lower flanks in adults, which gives rise to the common name. Adult Pacu possess flattened, molar-like teeth adapted for crushing hard seeds, nuts, and fruit rather than the piranha's sharp cutting teeth.

• Large, round, laterally compressed body, growing far bigger than related Silver Dollars
• Silvery-gray dorsal coloration transitioning to reddish-orange on the belly
• Flattened, molar-like teeth adapted for crushing seeds and fruit
• Robust, muscular body build compared to slimmer characins
• Deeply forked caudal fin
• Small, low-set dorsal fin similar in position to piranha relatives

Pacu are frequently mistaken for piranhas due to their similar body shape, but the flattened, human-like molar teeth, rather than sharp triangular teeth, and typically much larger adult size clearly distinguish them from any piranha species.

Pacu are native to the Amazon and Orinoco river basins of South America, inhabiting main river channels, tributaries, and extensively flooded forest habitats during high-water seasons. They favor warm, slow-to-moderately flowing water and rely heavily on seasonally inundated forest for feeding, where fallen fruit, seeds, and nuts become abundant during flood periods. Adults tend to move between deeper river channels during low water and expansive flooded forest areas when rivers rise, following the pronounced annual flood pulse typical of Amazonian hydrology. This strong dependence on flooded forest resources links Pacu populations closely to the health and connectivity of riparian forest along their native river systems.

Pacu are primarily herbivorous and frugivorous as adults, feeding heavily on fallen fruit, seeds, and nuts within flooded forest habitat, and in doing so play an important ecological role as seed dispersers across the Amazon basin. Juveniles supplement this diet with more insects and small invertebrates before shifting toward a largely plant-based diet with age. They are generally solitary to loosely social as adults, unlike the tighter shoaling behavior seen in smaller related characins, though juveniles may aggregate more readily. Reproduction involves migratory spawning movements timed with seasonal flooding, with eggs released into open water and no parental care provided afterward, relying on the flood pulse to disperse and support developing young.