The red bellied piranha is a large fish occurring in much of the Amazon basin (Brazil, Ecuador, Peru, Bolivia, and possibly Colombia), as well as the Río Essequibo (Guyana and Venezuela), some smaller, coastal drainages in north-east Brazil/the Guianas, and further south in the Río Paraná (Brazil, Paraguay, and Argentina) and Río Uruguay (Brazil, Uruguay, and Argentina). The red bellied piranha is found in most habitat-types across its range including major river channels, smaller tributaries, oxbows, floodplain lakes, and artificial lakes formed by dams.
The red bellied piranha grows to an adult size of nine to fourteen inches in length. Juvenile red bellied piranhas are a silver color with darker spots. Adults have a reddish tinge to the belly when fully grown. The rest of the body is often grey with silver flecked scales. Sometimes, blackish spots appear behind the gills and the anal fin is usually black at the base. The pectoral and pelvic fins may vary from red to orange. Females can be distinguished from males by the slightly deeper red color of their bellies. Females also generally attain a larger adult size and exhibit a more rounded body shape than males.
Juvenile piranhas form aggregations or schools for safety. Older individuals form loose groups and form dominance hierarchies, therefore the purchase of either a single specimen or group of 5 or more is recommended, with the latter being the preferable situation. Even when maintained in large groups in the aquarium, aggression may occur and slightly smaller or weaker individuals may be cannibalized.
The red bellied piranha should be maintained in an aquarium of 40 gallons or larger for a single specimen or an aquarium of 100 gallons or larger for a group of 5 or more. Standard aquarium gravel (CS7583) or sand make suitable substrates for the piranha aquarium. Other decor is at the preference of the aquarist, but live plants are often eaten. Excellent filtration is a must for these fish as they produce a lot of waste. multiple external filters are recommended. Trickle filters (AL2901) are also an excellent filtration option for the piranha aquarium and provide a safe place to install a heater. If the heater must be installed in the main aquarium, a heater guard is recommended as piranha have been known to damage submerged equipment.
Aim to change 30 to 50% of the tank volume each week to maintain good water quality. Always exercise extreme care when performing such maintenance or netting the fish for any reason. Care should be taken when maintaining the piranha aquarium, as they have been known to injure aquarists.
The red bellied piranha prefers a water temperature of 75°F to 82°F, a pH of 5.5 to 7.5, and a hardness of 2 to 12°H.
The red bellied piranha should generally be maintained in a species only aquarium. Some aquarists have had success maintaining these fish with much smaller fish such as tetras, or with large armored catfishes. There is no guarantee that any tank mates will be tolerated long term, however.
The red bellied piranha is easy to feed. In the wild it is not an exclusive carnivore and is more accurately described as an opportunistic generalist. The natural diet consists of live fishes plus aquatic invertebrates, insects, nuts, seeds, and fruits. Each jaw contains a single row of sharp, pointed, triangular teeth, which are used like blades to puncture, tear, chop, and crush. In the aquarium juveniles can be offered flakes, small pellets, blood worms (SF4792), small earthworms, chopped krill, and mussel, while adults will accept strips of fish flesh, silversides, whole prawns or krill (SF7137), mussels, live river shrimp, larger earthworms, and larger pellets.
The red bellied piranha should not be fed mammalian or avian meat since some of the lipids contained in these cannot be properly metabolized by the fish and may cause excess fat deposits and even organ degeneration. Similarly, there is no benefit in the use of ‘feeder’ fish such as live bearers or small goldfish, which carry with them the risk of parasite or disease introduction and tend not have a high nutritional value unless properly conditioned beforehand.