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
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.
Known Predators:
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
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.
Typical lifespan
Status: captivity: 15 to 25 years.
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
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 )
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
Commensal/Parasitic Species:
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
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)
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
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
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)
Piaractus brachypomus, the pirapitinga, is a large species of pacu, a close relative of piranhas and silver dollars, in the serrasalmid family.[1][2] It is native to the Amazon basin in tropical South America, but it formerly included populations in the Orinoco, which was described in 2019 as a separate species, P. orinoquensis.[3] Additionally, P. brachypomus is widely farmed and has been introduced to other regions.[4] In South Florida they are invasive in rivers, canals or lakes.[5]
As with a number of other closely related species, P. brachypomus is often referred to as the red-bellied pacu in reference to the appearance of the juveniles. 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.[6]
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In general, its behavior resembles that of the closely-related tambaqui (Colossoma macropomum). It is migratory, but the pattern is poorly understood.[7] Spawning occurs at the beginning of the flood season between November and February.[8] Larvae of the pirapitinga are found in whitewater rivers, but adults mainly live in flooded forests and floodplains of various river types, including those of both nutrient-rich and nutrient-poor.[7] Unlike the tambaqui, the pirapitinga also occurs in the headwaters of nutrient-poor rivers (not just in the lower sections).[7]
It mainly feeds on fruits, seeds, and nuts, but it is opportunistic and will also take zooplankton, Insects, crustaceans and small fish, especially in the dry season.[4][9] In general, more seeds are able to pass undamaged through the pirapitinga than the tambaqui, meaning that the former is overall a more efficient seed disperser.[10]
Piaractus brachypomus can reach up to 88 cm (2.9 ft) in length and 25 kg (55 lb) in weight.[2]
Juveniles have a distinct red chest and stomach, and are easily confused with the carnivorous red-bellied piranha (Pygocentrus nattereri), but the two can be separated by their teeth, which are molar-like in Piaractus brachypomus.[1] This similarity is believed to be Batesian mimicry by P. brachypomus in an attempt of avoiding predation by other species.[4] Adults lack the bright red chest and belly, and resemble the tambaqui (Colossoma macropomum), but can be separated by several meristic and morphological features: The pirapitinga has a smaller adipose fin that lacks rays, as well as differences in teeth and operculum.[1][11] The pirapitinga also has a more rounded head profile (less elongated and pointed).[11][12] The other member of its genus, P. mesopotamicus, can be distinguished by its smaller scale-size[13] and the higher number of lateral scales (more than 110).[1]
The pirapitinga supports major fisheries and based on a review by IBAMA, it was the 12th most caught fish by weight in the Brazilian Amazon in 1998 (just after the tambaqui).[7]
The pirapitinga is often kept in aquaculture. Hybrids between this species and the tambaqui have been produced in aquaculture.[14] It can also hybridize with P. orinoquensis, but the offspring appears to be sterile.[3]
{{cite web}}: CS1 maint: uses authors parameter (link) Piaractus brachypomus, the pirapitinga, is a large species of pacu, a close relative of piranhas and silver dollars, in the serrasalmid family. It is native to the Amazon basin in tropical South America, but it formerly included populations in the Orinoco, which was described in 2019 as a separate species, P. orinoquensis. Additionally, P. brachypomus is widely farmed and has been introduced to other regions. In South Florida they are invasive in rivers, canals or lakes.
As with a number of other closely related species, P. brachypomus is often referred to as the red-bellied pacu in reference to the appearance of the juveniles. 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.
