Name: Red-bellied Pacu
Other Names: Tambaqui, Pirapitinga
Scientific Name: Piaractus brachypomus
Family: Characidae or Serrasalmidae (considered Characidae: Serrasalmidae on FishBase)
Distribution: The basins of the Amazon and Orinoco Rivers.
Length: FishBase puts the maximum length at nearly 3' (88.0 cm). Two feet and longer are very common lengths attained in captivity.
Water Temperature: 73 to 82 degrees Fahrenheit (23-28 degrees Celsius)
Diet: They eat some insects in the wild but really love vegetation, especially that which is in a state of decay. They tend to do best in tanks where they are kept as vegetarians with a little bit of carnivore-based prepared food or small live foods fed occasionally.
Water Chemistry: Moderately hard water is appreciated (dH ~ 15)
Lifespan: 28 years max. reported by FishBase (it is likely that they live longer as many captive Pacus have been reported to have reached their silver birthday)
Species Description These are tall fish which give the appearance of a Red-bellied Piranha (Pygocentrus nattereri but they tend to be somewhat plumper despite the fact that the two are often confused. The most significant morphological difference between the two is the the level of protrusion of the jaw (much smaller in pacus than in piranhas). This helps to illustrate the largely vegetarian nature of the pacu and the largely carnivorous nature of the piranha.
They are both gray or silvery fish with red bellies and the pacu has red lower body fins as well. The tambaqui also grows to a size which Pygo. nattereri can never hope to achieve.
The genus to which the tambaqui formerly belonged, Colossoma was, at the time, the only genus of fish in which true molars are present. All genera which sprang from Colossoma are now among that still-somewhat-small assortment.
Though they aren't to be feared as much as piranhas, tambaquis have formidable teeth which will be used on careless keepers that anger or scare them. The name Serrasalmidae means "Salmons with a Saw" (David Schleser, "Piranhas: A Complete Owners' Manual"), and this accurately describes the dentition of the Pacus.
Species Behaviour Pacus do best when kept in shoals when they are young but have been found to live solitarily in the wild as they age.
They are known to dispatch glass-encased heaters with some regularity and should thus be either shielded from them or kept warm via titanium heaters.
Natural Conditions The young are found solely in shallow blackwater, but the adults will be found throughout the Amazon-Orinoco, especially the flooded forests during the rainy season. (Where else would they get their rotting fruit and tree nuts?)
Natural Range The basins of the Amazon and Orinoco Rivers.
Minimum recommended tank size 300 gallons with at least 200 gallons/extra Pacu
Water Temperature 73 to 82 degrees Fahrenheit (23-28 degrees Celsius)
Water Quality Moderately hard water (dH ~ 15) that is alkaline to neutral (pH 5-7) is most appreciated, but softer water is acceptable.
Sexing The males, with their pointed dorsals and intense red coloration, become sexually mature at age three, while their female counterparts must wait until age four to come into season.
Breeding Not accomplished in aquaria, but the Houston Zoo reports that females lay smooth, spherical eggs which are subsequently fertilized by their male counterparts. The pair then abandons the eggs. At some point, hatching occurs, but the length of the incubation period is unknown.
Feeding They eat some insects in the wild but really love vegetation, especially that which is in a state of decay. They tend to do best in tanks where they are kept as vegetarians with a little bit of carnivore-based prepared food or small live foods fed occasionally. Romaine lettuce, all sorts of fruits and clippings from aquarium plants are readily taken. They can also crack nuts easily and may be given those on occasion.
Miscellaneous Info This is the most common Pacu and, as such, is known simply as "Pacu" in some regions of North America.