The natural range of red-bellied pacu extends from 23°N to 11°S latitude, in the Amazon and Orinoco river basins/flood plains. Common names for this species vary by region. It is known as pirapitinga in Brazil, paco in Peru and cachama blanca in Colombia. Introductions of red-bellied pacu populations have been reported in many regions around the globe, in places as unlikely as Vancouver, British Columbia. Occurrences such as these are most likely a result of fish outgrowing hobbyists’ aquariums and the owners releasing fish into local waters. Red-bellied pacu were introduced to India sometime between 2003 and 2004 from Bangladesh and have become the focus of several aquaculture projects.
Biogeographic Regions: oriental (Introduced ); neotropical (Native )
occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Year-round
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: Native to Orinoco and Amazon basins, South America. Reported from 16 states (Fuller et al. 1999) but evidently not established in the United States.
Red-bellied pacu are often confused with other pacu (Piaractus mesopotamicus, Colossoma macropomum) or piranha (Pygocentrus nattereri) species, due to their similar appearance. The body is deep and laterally compressed, with silvery sides (becoming darker approaching the dorsum) and red coloration on the belly, chin, pectoral fins, and occasionally the leading rays of the anal fin. The remaining rayed fins are uniformly dark-colored. As in other characin species, a small, unrayed adipose fin is present approximately midway between the dorsal and caudal fins. The dorsal fin contains 15-18 rays, the pectoral fins 16-19, the anal fin 24-28, and the pelvic fins 8. The first few rays of the dorsal and anal fins are longer than the remaining elements. A row of sharp serrae formed by modified scales is found on the abdomen. Although not as well-developed and sharp as in their piranha cousins, red-bellied pacu have two rows of hard, flattened teeth used for crushing seeds and nuts. This dentition is comprised of 2 series of molariform incisors located on the premaxilla and 1 row of dentary teeth. The largest individuals can weigh up to 25 kg and measure 88 cm, though these numbers are usually lower in captivity. Smaller captive sizes are most likely due to insufficient nutrition; the notion that ‘they will grow to fit their environment’ is a widespread myth.
As juveniles, red-bellied pacu mimic piranha by displaying dark grey to black spots on the body, a standard characteristic of piranha. This wards off attacks by predators, including piranha themselves, when pacu are at a vulnerable age. As pacu get older and surpass the size of an average piranha, the spots disappear.
Range mass: 1 to 25 kg.
Range length: 25 to 88 cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes alike
As fry and juveniles, red-bellied pacu can be found in and around floodplains of nutrient rich tributaries, or in headwaters when nutrients are poor. Pacu move further out into main waterways as they mature. Optimal water pH is 6.8, with an optimal temperature of 26°C. Considered a mid level swimmer, this species is found at depths of up to 8 meters.
Range elevation: <100 m (Amazon basin) to >1000 (Orinoco basin) m.
Range depth: 0 to 8 m.
Habitat Regions: tropical ; freshwater
Aquatic Biomes: rivers and streams
Wetlands: marsh ; swamp
Habitat Type: Freshwater
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: No. No populations of this species make annual migrations of over 200 km.
The dietary composition of red-bellied pacu (and a number of closely related species) shifts depending on the season. During the wet season, they rely heavily on seed predation from the newly dropped fruit of riparian trees and plants. Although red-bellied pacu are widely considered to be frugivores, they are actually omnivorous, also eating crustaceans and smaller fishes, especially in the dry season. As some of the largest fish in the Amazon, pacu require large amounts of food. They feed in multiple “bite events”, with each event containing a number of individual bites, which is similar to the feeding behavior observed in true piranhas.
Animal Foods: fish; insects; mollusks; aquatic crustaceans
Plant Foods: leaves; seeds, grains, and nuts; fruit
Other Foods: detritus
Primary Diet: carnivore (Piscivore , Insectivore , Molluscivore ); herbivore (Frugivore , Granivore ); omnivore
The role of pacu species is integral to the growth and development of the Amazonian habitat. With the rise of seasonal flood waters, their diet shifts almost exclusively to seeds and nuts from the trees and plants that line the river, making these fish an important vehicle of seed dispersal. A study of the contents of pacu stomachs recorded seeds from 27 tree and 26 non-woody plant species. This relationship has been negatively impacted by climate change, ranching, irresponsible farming practices and logging.
Ecosystem Impact: disperses seeds
- Anacanthorus penilabiatus (Monogenea: Dactylogyridae)
- Mymarothecium viatorum (Monogenea: Dactylogyridae)
- Dadaytrema oxycephala (Trematoda: Cladorchiidae)
Information regarding specific predators of red-bellied pacu is not available. Larger fishes and wading birds likely represent the greatest predatory threat to juveniles. The large size attained by adult pacu would protect them from all but the largest predatory fish species, such as pirarucu (Arapaima gigas). Black caiman (Melanosuchus niger) are another likely predator of adult red-bellied pacu. Pacu are popular aquaculture species and native populations are subject to predation by humans.
- humans (Homo sapiens)
Diseases and Parasites
Life History and Behavior
Pacu, like other characins, can be very sensitive to environmental disturbances. In addition to the normal range of sounds detectable by other fishes, they can detect higher-pitched sounds through the use of a modified osteological complex (composed of several anterior vertebra and other bones and known, collectively, as the Weberian apparatus) that bridges the swim bladder with their inner ear.
Pacu are capable of intraspecific communication using an alarm chemical known as "Schrekstoff". If one fish is injured, this substance is discharged from the wound into the water, alerting nearby conspecifics and related species of possible danger.
Pacu species also use their lateral line system when identifying movement in the water, which aids in maintaining proper shoaling behavior.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: mimicry ; pheromones ; vibrations
Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical
Eggs generally hatch between 12 and 20 hours after fertilization. At birth, fry are approximately 2 mm long and weigh .16 grams. By the time that they hatch, pacu fry have a fully developed nervous system with a heightened number of neurons in the fore- and hindbrain. This is believed to correspond to the main motor cortex and allows quicker reaction by tail muscles in prey acquisition or predator escape. After a month, juveniles more than quadruple in weight and almost double in size. Pacu reach sexual maturity around 3 years of age. Except for the body spots displayed by juveniles, young fish look similar to adults.
Development - Life Cycle: indeterminate growth
Red-bellied pacu are long-lived fish, with popular aquarium sites quoting life spans of 25 years and beyond. One account by MSNBC reported on a 43 year old black pacu Colossoma macropomum, a similar species that is often confused with its red-bellied relative.
Status: captivity: 15 to 25 years.
During spawning, females scatter adhesive eggs; fertilization then occurs externally. Although parents abandon their eggs, pacu are brood hiders, minimizing the chances of the clutch being discovered by predators and scavengers.
Mating System: polygynandrous (promiscuous)
Breeding occurs in annual cycles with the onset of the wet season. Spawning begins as early as November, when the waters first begin to rise, and can last through February. Prime spawning conditions are achieved at 4.0 mg/L of oxygen and 27°C. Spawning is preceded by the release of just a few eggs by females and a ‘knocking’ sound produced by the males. On average, eggs measure 1.2 mm across and weigh just above 1.6 mg. In large pacu species, mature females lay an average of 150,000 eggs, though this number can occasionally reach 1,000,000. After laying a clutch, females can be ready to spawn again in 10 weeks. Although males produce sperm year-round, one study found that females were sensitive to seasonal cycles and sometimes would not ovulate even after artificial induction.
Breeding interval: Pacu spawn annually, sometimes multiple times during a single spawning season.
Breeding season: Spawning occurs during the rainy season (usually from September to February).
Range number of offspring: 1,000,000 (high) .
Average number of offspring: 150,000-200,000.
Range gestation period: 12 to 20 hours.
Range age at sexual or reproductive maturity (female): 2 to 4 years.
Range age at sexual or reproductive maturity (male): 2 to 4 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); broadcast (group) spawning; oviparous
Besides attempts to hide egg clutches, pacu eggs and juveniles receive no parental care.
Parental Investment: pre-hatching/birth (Protecting: Female)
Molecular Biology and Genetics
Barcode data: Piaractus brachypomus
Below is the sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen.
Other sequences that do not yet meet barcode criteria may also be available.
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Download FASTA File
Statistics of barcoding coverage: Piaractus brachypomus
Public Records: 7
Specimens with Barcodes: 7
Species With Barcodes: 1
Although this species has not been evaluated by IUCN Red List, native populations are facing increased stress due to commercial fishing demands, with both legal harvest and poaching leading to population declines. Furthermore, with growing demands for food production, agriculture is now threatening populations of red-bellied pacu. A study examining the effects and lethal concentrations of chemicals in the herbicide Roundup, widely used on coca and poppy crops in the region, found that pacu exposed to the herbicide, even at low levels, developed lesions and showed possible nervous system damage that could negatively affect future reproduction.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
National NatureServe Conservation Status
Rounded National Status Rank: NNA - Not Applicable
Rounded National Status Rank: NNA - Not Applicable
NatureServe Conservation Status
Rounded Global Status Rank: GNR - Not Yet Ranked
Relevance to Humans and Ecosystems
Concerns have been raised about the potential impact of red-bellied pacu as an invasive species. Due to their large size and food requirements, it may easy for pacu to outcompete native species. Hybridizations of red-bellied pacu with common carp Cyprinus carpio carpio and other exotic species are also currently being tested. Although these cross-species strains are intended to establish favorable traits for aquaculture, the intelligence of developing hybrid fish with a voracious appetite and the ability to survive in local waterways, should they somehow be released, has been questioned on a number of occasions.
Negative Impacts: injures humans (bites or stings)
As robust, rapidly growing species prized for their meat in many South American countries, pacu are increasingly attractive candidates for sustainable aquaculture projects in many regions. A recent increase in research on red-bellied pacu shows clear links to these commercial interests, with many studies focusing on optimal feeding strategies. Not all pacu farming is large scale, as pacu are cultured in many rural areas for use as a direct food source or income supplement. Hybridization of red-bellied pacu and other closely related species is being explored to combine the most favorable aquacultural attributes of these fishes.
Positive Impacts: pet trade ; food
Piaractus brachypomus (or Colossoma bidens, a synonym that used to be very popular) is an Amazonic pacu, a close relative of piranhas and silver dollars. As with a number of other closely related species, P. brachypomus is often referred to as the red-bellied pacu. This has resulted in a great deal of confusion about the nature and needs of all the species involved, with the reputation and requirements of one frequently being wrongly attributed to the others. An unambiguous name for P. brachypomus is pirapitinga.
P. brachypomus can and will grow quickly under favourable conditions. The overall size to which it can grow remains a matter of considerable debate and no small amount of confusion. Much of the confusion stems from the fact that one species can and often is easily mistaken for another, and the size attainable in captivity is usually less than the size attainable in the wild. P. brachypomus is a comparatively smaller species. However, it can easily outgrow the majority of home aquaria: they are strong and robust fish which need a lot of swimming space and make very heavy demands of the filtration system.
Diet in captivity
P. brachypomus is mainly a herbivorous species, but, in fact, it's truer to say that it is an opportunist feeder. Stomach analyses of wild specimens show it to be primarily a herbivorous species, feeding on fruits, nuts and seeds. It is an opportunist, though, and also takes insects, zooplankton and small fish. In the aquarium offer it a varied diet consisting of quality dried pellets or floating sticks, along with plenty of fruit and vegetables. Spinach, lettuce leaves, and fruit and vegetables such as apple, banana, peach, grapes, courgette, peas, cabbage and carrot all work well.  They will also sometimes "snatch" floating food, which results in a lot of splashing and makes a lid essential. In captivity, it is inadvisable to keep this species with anything small enough to be regarded as food, though they are usually safe around larger fish.
At larger sizes, the P. brachypomus needs a correspondingly large tank to thrive in captivity. The temperature of the water in which they are kept should be within 78–82 °F (26–28 °C) and the system should be well filtered and oxygenated. Larger P. brachypomus are sometimes classed as "monster fish" and find a place in aquariums which house other large fish. They tend to be timid and retiring and will retreat to cover if they feel insecure. Some squabbling may become apparent if they are kept in a group.It can take a lot of time for them to get accustomed to the aquarium, and may try to jump out frequently.
- NAS – Nonindigenous Aquatic Species, Piaractus brachypomus
- Gamefish of the Amazon Basin, Tambaqui and Pirapitinga
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Names and Taxonomy
Comments: Colossoma bidens and Colossoma brachypomum are widely used synonyms (see Fuller et al. 1999).
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