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Pacu
Large pacu at the Shedd Aquarium
Large pacu at the Shedd Aquarium
Scientific classificationEdit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Characiformes
Family: Serrasalmidae
Genera

Pacu (Portuguese pronunciation: [paˈku]) is a common name used to refer to several species of omnivorous South American freshwater serrasalmid fish related to piranhas. Pacu and piranha do not have similar teeth, the main difference being jaw alignment; piranha have pointed, razor-sharp teeth in a pronounced underbite, whereas pacu have squarer, straighter teeth and a less severe underbite or a slight overbite.[1] Pacu, unlike piranha, mainly feed on plant material and not flesh or scales.[2] Additionally, the pacu can reach much larger sizes than piranha, up to 1.08 m (3 ft 6+1⁄2 in) in total length and 40 kg (88 lb) in weight.[3]

Name

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The common name pacu is generally applied to fish classified under the below listed genera.[4] Among these, several genera contain species where commonly used English names include the word pacu, as listed.[5][6]

Each of these groups contains one or more separate species. For example, the fish often found in pet stores, known as the black pacu and red-bellied pacu, typically belong to the species Colossoma macropomum and Piaractus brachypomus, respectively.[7][8] A species popular among fish farmers is Piaractus mesopotamicus, also known as Paraná River pacu or small-scaled pacu.[9]

Pacu is a term of Tupi-Guaraní origin. When the large fish of the genus Colossoma entered the aquarium trade in the U.S. and other countries, they were labeled pacu. In the Brazilian Amazon, the term pacu is generally reserved to smaller and medium-sized fish in the Metynnis, Mylossoma, Mylesinus and Myleus genera. Colossoma macropomum are known as tambaqui, whereas Piaractus brachypomus is known as pirapitinga. In Peru, both of the species (Colossoma macropomum and Piaractus brachypomum) are called pacú and gamitana. Piaractus mesopotamicus of the Paraná-Paraguay basin is also called pacú in Paraguay and Argentina.[10]

Classification

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Colossoma macropomum (black pacu), at the New England Aquarium

Pacu, along with their piranha relatives, are a characin fish, meaning a kind of tetra, belonging to the Characiformes order. The ongoing classification of these fish is difficult and often contentious, with ichthyologists basing ranks according to characteristics that may overlap irregularly. DNA research sometimes confounds rather than clarifies species ranking. Ultimately, classifications can be rather arbitrary.[11]

Pacu, along with piranha, are currently further classified into the family Serrasalmidae (formerly a subfamily of Characidae). Serrasalmidae means "serrated salmon family" and refers to the serrated keel running along the belly of these fish. However, dental characteristics and feeding habits further separate the two groups from each other.[11]

Native distribution and habitat

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Pacus are native to tropical and subtropical South America. They inhabit rivers, lakes, floodplains and flooded forests in the Amazon, Orinoco, São Francisco River and Río de la Plata Basins, as well as rivers in the Guianas. Here they form part of the highly diverse Neotropical fish fauna. Their habitat preferences varies significantly depending on the exact species. Several species are migratory.[12]

As exotic species

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watercolor of a Pacu
19th century watercolor of a Pacu painted by Jacques Burkhardt

Pacus have been introduced to the wild in many places outside their native range, both in South America and other continents. They are sometimes released to increase the local fishing, but others are released by aquarists when they outgrow their aquarium. This is illegal in many countries and strongly advised against.[7][8] When becoming established they can be invasive species that damage the local ecosystem.[13] In many regions where individuals have been seen they are unlikely to survive long-term because of temperature. Among the large pacu species (Colossoma and Piaractus), the most cold-adapted species is Piaractus mesopotamicus, which tolerates water down to 15 °C (59 °F), but stops feeding below 18 °C (64 °F).[14]

United States

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Pacus have become established in Puerto Rico and singles have been caught in numerous U.S. states.[15] Discoveries have been reported in Alabama,[16] Arizona,[17] Arkansas,[1] California,[18] Colorado,[19] Florida,[20][21] Georgia,[22] Hawaii,[15] Iowa, Idaho,[23] Illinois,[24] Indiana,[25] Kansas,[15] Kentucky,[26] Maine,[27] Maryland,[28] Massachusetts,[29] Michigan,[30] Minnesota,[31] Mississippi,[15] Missouri,[32] Nebraska,[33] New Hampshire,[34] New Jersey,[35] New York,[15] North Carolina,[36] North Dakota,[37] Ohio,[38][39] Oklahoma,[40] Pennsylvania,[41] South Carolina,[42] Texas,[43][44][45] Utah,[46] Washington,[47] Wisconsin,[48] and Wyoming.[49] Among the numerous recent records are a pacu caught in the California Delta, near Stockton in 2015,[50] two in Lake St. Clair in 2016 and a single in Lake Huron in 2016.[51]

Some state wildlife authorities have advised home aquarists who wish to get rid of overgrown pacu to cut the heads off the fish and dispose of them as garbage.[48] Habitattitude, a U.S. national initiative led by the Aquatic Nuisance Species (ANS) Task Force, recommends humanely disposing the fish through a veterinarian or pet retailer, returning them to retailers, or donating them to a local aquarium society, school, or aquatic business.[52] Additionally, aquarium-raised fish can be eaten (see Food fish).[53]

Colossoma macropomum, a pacu, for sale in the Manaus Fish Market, Brazil. This fish was approximately 85 cm (33+1⁄2 in) long.

Europe

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In August 2013, a pacu was discovered in Scandinavian waters; a fisherman pulled a 21 cm (8+1⁄2 in) specimen from the Øresund, a semi-brackish strait between Sweden and Denmark.[54]

An angler fishing on the river Seine in Paris, France, caught a pacu in August 2013.[55]

In June 2016, a 20 cm (8 in) pacu was caught in a city pond in Tula, Russia.[56]

In June 2017, a pacu was accidentally caught during a fishing contest at the Port of Drobeta Turnu Severin, Romania. The fish bit one of the fishermen, leading to a general warning being issued in the region, until the origin of the fish can be determined.[57]

In August 2017, a pacu was caught in the stream Motala Ström in Norrköping, Sweden.[58]

In July 2019, two pacus were caught near Baia Mare, Romania.

In September 2020, a 50 cm (20 in) pacu weighing approx. 3 kg (7 lb) was caught in Zegrze Reservoir in Poland.[59]

In February 2024, a dead pacu was found in Garadice Lough, Ireland.[60][61]

In Summer 2025 a pacu got fished out of the Jagst River near Crailsheim in southern Germany. [62]

Asia

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Pacus have become established in tropical Asia, including Vietnam, Malaysia, Bangladesh,[63] Thailand,[63][64] and India.[65]

New Guinea

[edit]

Pacu were introduced in 1994 to the Sepik River, and in 1997 to the Ramu river as a food source, due to overfishing of native species. Local people blame the fish for outcompeting native species, including juvenile crocodiles, as well as for several attacks on humans. As a primarily vegetarian fish, red-bellied pacu, have also consumed the floating mats of vegetation in the Sepik River, which operated as fish nurseries and crocodile and bird nesting sites. Thus the entire ecosystem has become impoverished and local people cannot subsist as easily as they once did.[13]

Importance to humans

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In their native range, pacus are widely fished and farmed. Based on a study by IBAMA, Colossoma macropomum, Piaractus brachypomus and Mylossoma spp. are all in the top-15 of the most caught fish (by weight) in the Brazilian Amazon.[12]

Aquaria

[edit]
A young red-bellied pacu

Pacu are commonly sold as "vegetarian piranhas" to home aquarium owners. With the proper equipment and commitment, pacu have been known to make responsive pets. One such example was Swish, a 75-cm (30-inch) pacu owned for over 20 years by a Chinese restaurant (Kau Kau) in the Chinatown district in Seattle, Washington; one aquarium technician said of Swish, "He'd rub his body on your arms, kind of like a dog."[66]

However, there is some question of whether the fish are a good choice for the typical aquarist. While they are not aggressive carnivores like the piranha, their crushing jaw system, used primarily for eating seeds and nuts, can be hazardous. One toddler needed surgery after a pacu (misreported as a piranha) bit her finger at Edinburgh Butterfly and Insect World in Scotland. Commenting on the incident, Deep Sea World zoological manager Matthew Kane warned, "Pacus will eat anything, even children's wiggling fingers."[67]

If a large population of pacu enters an ecosystem to which it is not native, the fish can have a very adverse effect. Pet stores sell pacu as small as 5–8 cm (2–3 in) long and neglect to warn customers that fish growth is not inhibited by tank size, contrary to popular fish lore.[4] "Most UK dealers now refuse to stock this species due to the large size and expensive aquarium requirements it demands," according to Practical Fishkeeping magazine's Matt Clarke.[68] Incapable of maintaining large aquaria, overwhelmed hobbyists are suspected of illegally releasing their pacu into wild waterways. As tropical fish, pacu will die in cold weather; as newcomers to an ecosystem, pacu may out-compete native species for available food, habitat, and other resources, or displace them by introducing exotic parasites or diseases. Most wildlife resource authorities prohibit releasing exotic fish, including pacu, into the wild. Officials of one Texas lake have put a $100 bounty on the pacu caught there.[69]

Game fish

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In Appendix B of Through the Brazilian Wilderness[70] (see also online version[71]), Theodore Roosevelt advised, "For small fish like the pacu and piranha an ordinary bass hook will do." Concerning the pacu, he added:

"A light rod and reel would be a convenience in catching the pacu. We used to fish for the latter variety in the quiet pools while allowing the canoe to drift, and always saved some of the fish as bait for the big fellows. We fished for the pacu as the native does, kneading a ball of mandioc farina with water and placing it on the hook as bait. I should not be surprised, though, if it were possible, with carefully chosen flies, to catch some of the fish that every once in a while we saw rise to the surface and drag some luckless insect under."

More recently, South American rivers including the Amazon have become a popular destination for recreational anglers, who go to fly fish for pacu. The International Game Fish Association has sponsored fly-fishing courses for native Brazilian fishermen, typically accustomed to subsistence fishing, so they can work as guides to fishing tourists.[72]

When bait-fishing in pacu-stocked ponds, anglers in Malaysia are advised to use circle hooks, size 2 or larger, and braided leather rather than nylon leaders which are easily broken by the pacu's teeth. Since pond pacu often nibble at the bait before taking it, anglers should let them swim away with the bait. If the angler simply allows the line to tighten, the circle hook will slide to the side of the fish's mouth and embed its point there.[73]

Grilled pacu over rice with sides of lettuce, tomato, onions, and plantains, with a lemon-half garnish.
Photograph taken in Villa Tunari, Bolivia, by Marc Alan Davis.

Food fish

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Theodore Roosevelt wrote of catching and eating pacu in his book Through the Brazilian Wilderness.[70][71] He described them as "good-sized, deep-bodied fish," and noted, "They were delicious eating."

Today, the Amazon river is experiencing a crisis of overfishing. Both subsistence fishers and their commercial rivals compete in netting large quantities of pacu, which bring good prices at markets in Brazil and abroad.[74]

Aquaculture may relieve the overfishing crisis, as well as improve food security by boosting fish supplies. Various species of pacu are increasingly being used for warm-water farm fishing around the world.[75] Pacu are considered ideal for their tolerance of the low-oxygen water in farm ponds. They also don't require a lot of expensive protein in their diet, and can be raised year-round in warm or temperature-controlled environments.[76]

Research shows that the "flavor of [farmed] pacu is comparable to that of hybrid striped bass, tilapia, and rainbow trout, but superior to catfish."[77] In South America, pacu are prized for their sweet, mild flavor.

Aquarium-raised pacu can be cooked and eaten, but care should be taken to ensure that no toxic medications were used in the aquarium.[4] A recipe and preparation instructions are provided on the Greater Seattle Aquarium Society's Web site.[53]

Incorrect claim of testicle-biting

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In 2013, a pacu was caught in the Øresund, a strait between Sweden and Denmark.[78] This led to media reports mistakenly warning that the fish could attack testicles. The reports were based on a joke (referring to their actual feeding on tree nuts) that was not meant to be taken seriously.[78] Nevertheless, their very strong jaws made for crushing plant seeds and the like means that fishermen and aquarists sometimes are warned about the powerful bite that may cause traumatic injuries.[3][7][8]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Pacu

View on Grokipedia
from Grokipedia
Pacu is a for several species of omnivorous to herbivorous in the family Serrasalmidae, within the order , native to tropical and closely related to the more carnivorous , distinguished primarily by their peaceful temperament and . These fish are characterized by robust, deep-bodied forms with distinctive square, flat, human-like teeth adapted for crushing fruits, nuts, and seeds, and prominent species include the black pacu (Colossoma macropomum, also known as ), red-bellied pacu (), and silver pacu (Piaractus mesopotamicus). Native to the river basins of the , , Paraguay-Paraná, and in countries such as , , , , and , pacu inhabit diverse freshwater environments including main river channels, floodplains, lakes, and seasonally flooded forests, preferring warm, slow-moving waters with temperatures between 22–28°C and levels of 5.0–7.8. During flood seasons, they migrate into inundated vegetation to access food resources, while in dry periods, they concentrate in deeper river sections. Adults can grow to lengths of up to 108 cm and weights exceeding 40 kg, with juveniles displaying an ovoid to rhomboidal body shape that elongates with age, often featuring dark dorsal coloration and lighter ventral sides. Pacu are primarily frugivorous, consuming fruits, seeds, and nuts that fall into rivers (comprising up to 44% of their diet during high-water periods), supplemented by , aquatic plants, and occasionally small or , which aids in and nutrient cycling within their ecosystems. They exhibit schooling behavior and non-aggressive social structures, foraging at the surface or mid-water levels, and reproduce through migratory spawning tied to seasonal floods, with gonadal development occurring in individuals over 56 cm in length. In their native range, pacu play a vital ecological role as key consumers in floodplain food webs, while commercially, like C. macropomum are extensively farmed in for their mild-flavored, protein-rich flesh, supporting in . However, introduced populations in regions like the , , and pose risks as due to their rapid growth and potential to alter local aquatic ecosystems.

Taxonomy and nomenclature

Etymology and common names

The term "pacu" originates from the Tupi-Guarani languages spoken by , where it is believed to derive from words denoting a "quick eater" or "fast eater," reflecting the fish's rapid feeding behavior on fruits and seeds. This linguistic root highlights the cultural significance of these fish among Amazonian communities, who observed their voracious consumption of falling fruits from riverbank trees. In English-speaking regions, "pacu" serves as the primary common name for various species in the Serrasalmidae family, often distinguishing them from their carnivorous relatives, the piranhas, to avoid nomenclature confusion—though both terms stem from Tupi-Guarani origins. Specific variations include "red-bellied pacu" for Piaractus brachypomus, noted for its reddish abdomen, and "silver pacu" for Piaractus mesopotamicus, while species in the genus Metynnis (known as silver dollars) are prized in the aquarium trade for their metallic sheen. Portuguese speakers in commonly use "pacu" generically, with regional specifics like "tambaqui" for Colossoma macropomum, the largest and most commercially important . In Spanish, names such as "cachama," "gamatana," or "paco" prevail in countries like and , while indigenous terms like "pirapitinga" persist in Amazonian dialects for certain fruit-eating variants. These names evolved through colonial interactions, blending native Tupi-Guarani with European languages. The scientific nomenclature for pacu species traces back to early 19th-century European explorations, with formally describing Colossoma macropomum in , adopting local names into binomial Latin forms that emphasized physical traits like large fins ("macropomum" from Greek for "large fin"). Subsequent descriptions, such as for Piaractus genera in the by Cuvier and , incorporated "pacu"-derived terms to denote their robust, herbivorous nature, solidifying the common names in ichthyological literature.

Classification and species diversity

Pacu are classified within the order , family Serrasalmidae, which encompasses both pacu and as Neotropical characiform fishes native to South American freshwater habitats. The family Serrasalmidae was elevated from subfamily status (Serrasalminae within ) in recent taxonomic revisions, reflecting phylogenetic analyses that support its distinct based on molecular and morphological data. The primary genera associated with pacu include Colossoma and Piaractus, which comprise the most economically and ecologically significant species. In Colossoma, notable species are C. macropomum (tambaqui) and C. bidens (black pacu), while Piaractus includes P. brachypomus (red-bellied pacu) and P. mesopotamicus (small-scaled pacu). Other genera such as Mylossoma and Myloplus also contribute to pacu diversity, with pacu generally referring to the herbivorous members of Serrasalmidae distinguished from carnivorous piranhas. As of 2025, approximately 10-12 species are commonly recognized as pacu, though the broader Serrasalmidae family includes over 100 species; this count focuses on those with primarily frugivorous or herbivorous diets in genera like Colossoma, Piaractus, and Myloplus. Recent taxonomic revisions have expanded this diversity, including the description of Myloplus nigrolineatus in 2020 from the Brazilian Amazon based on integrative morphology and genetics, and two new species in 2024: M. sauron and M. aylan (Lord Sauron pacu and Aylan's pacu), identified through molecular divergences and bar pattern differences in the upper Madeira River basin. Historically, pacu were initially lumped with in early 20th-century classifications due to shared serrated , but were separated starting in the mid-1900s based on differences in morphology—pacu exhibit molariform teeth adapted for crushing fruits and seeds, contrasting with the slicing teeth of —and dietary specialization, with pacu being predominantly herbivorous or omnivorous. This distinction was reinforced by phylogenetic studies in the 2010s and 2020s, which traced dietary shifts and across Serrasalmidae. Ongoing debates surround pacu boundaries, particularly due to hybridization in , where interspecific crosses between Piaractus species or with Colossoma produce viable offspring that can blur morphological and genetic distinctions, complicating identification in and potentially impacting wild through escapes. Such hybrids are often more resilient but raise concerns about genetic pollution and the need for regulatory management in breeding programs.

Physical characteristics

Morphology and anatomy

Pacu, members of the family Serrasalmidae, possess a distinctive characterized by a deep, laterally compressed form that facilitates maneuverability in dense aquatic vegetation of riverine habitats. This robust, somewhat rounded or plate-shaped body is covered in large, silvery scales that provide in turbid waters, with some exhibiting vibrant red markings on the belly, chin, and pectoral fins, such as in . The caudal fin is typically forked, aiding in agile swimming, while an adipose fin is present posterior to the . A prominent feature shared across the family is a bony, serrated along the ventral midline, extending from the gular region to the anus, which varies in shape from ovoid in thicker-bodied taxa to more pointed in narrower and supports structural integrity during locomotion. In contrast to their carnivorous relatives , pacu feature specialized adapted for processing tough plant material. The oral jaws bear broad, tricuspid teeth arranged in two rows on the and one row on the dentary, with flattened, molariform shapes resembling human molars that enable grinding and crushing of seeds, fruits, and vegetation. These teeth often display red pigmentation toward the cutting edges due to iron enrichment in the enameloid, enhancing hardness and wear resistance for a durophagous diet; for instance, in , the primary cusp is well-developed with smaller secondary cusps. Sensory structures in pacu are well-suited to their freshwater environments, including large eyes with variable orbit sizes that accommodate vision in low-light conditions prevalent in shaded river systems. The lateral line system, consisting of mechanoreceptors along the body, detects water vibrations and movements, crucial for schooling and predator avoidance in flowing waters. Additionally, the Weberian apparatus connects the inner ear to the swim bladder, allowing sensitivity to high-frequency sounds. Sexual dimorphism in pacu is generally subtle, with many species like showing no marked differences between sexes in body shape or coloration. However, in certain genera such as Myloplus, mature males exhibit an elongated lobe in the anal fin formed by extended middle rays, along with intensified coloration patterns during breeding, such as darker dorsal hues or fins with pigmented margins. Adaptations for herbivory extend beyond oral to include robust pharyngeal jaws equipped with grinding plates, which process ingested matter after initial mastication, as seen in like the (Colossoma macropomum). The digestive system features specialized enzymes, such as elevated and activities in the intestine, facilitating the breakdown of carbohydrates and fibrous vegetation, with responses varying by diet composition in Piaractus mesopotamicus.

Size, growth, and lifespan

Pacu species exhibit significant variation in size, growth patterns, and lifespan across genera, with Amazonian Colossoma species generally attaining larger dimensions than Piaractus species from the Paraná basin. Colossoma macropomum, for instance, can reach a maximum total length of 108 cm and weight of 40 kg in the wild, though common adult sizes are around 70 cm. In contrast, Piaractus brachypomus achieves up to 88 cm in total length and 25 kg, while Piaractus mesopotamicus typically maxes at approximately 50-60 cm total length and 20 kg, reflecting adaptations to different riverine environments. Growth in pacu is rapid during the juvenile phase, particularly in optimal conditions where lengths can increase by up to 20 cm per year, driven by high water temperatures (28-30°C) and abundant protein-rich feeds. This rate slows after around 2-3 years, with annual weight gains peaking at 3.3 kg for C. macropomum between ages 4 and 5 before tapering due to metabolic shifts. In settings, growth is more variable, constrained by availability like fruits and during floods, resulting in slower overall development compared to captive rearing where specific growth rates can exceed 2.5% body weight per day in juveniles. Factors such as stocking density and dissolved oxygen further modulate these patterns, with overcrowded conditions reducing growth efficiency in Piaractus species by up to 20%. Lifespan varies between 10-20 years in the wild for most pacu, limited by predation and environmental stressors, but can extend to 25-28 years in controlled environments with reduced disease pressure and consistent nutrition. For example, P. brachypomus has a reported maximum age of 28 years, while C. macropomum commonly lives 15-20 years in rivers but benefits from extended longevity in farms. Ontogenetic changes include shifts in coloration from vibrant juvenile hues—such as red ventral regions in Piaractus—to more subdued silver or dark adult tones in Colossoma, aiding in open waters. Fin elongation occurs progressively, with dorsal and anal fins extending relative to body size during maturation, enhancing stability in adults. These transformations underscore the adaptive progression from fast-growing larvae to robust, long-lived adults across pacu species.

Biology and ecology

Diet and feeding behavior

Pacu species, such as Colossoma macropomum and Piaractus mesopotamicus, exhibit a primarily herbivorous diet consisting of fruits, seeds, nuts, aquatic vegetation, and fallen leaves, with opportunistic consumption of , small , or during periods of scarcity. This frugivorous tendency supports their role as key consumers of allochthonous material from floodplain forests, where they selectively ingest nutrient-rich plant matter while largely avoiding animal prey unless plant resources are limited. In terms of foraging behavior, pacu often school in large groups during fruiting seasons to access surface-floating fruits and seeds in flooded riverine forests, employing feeding to capture items and using robust, molar-like teeth to tough seed coats and vegetation. These adaptations enable efficient processing of hard material, contrasting with the slicing of related carnivorous species. Unlike , which engage in aggressive pack hunting for flesh, pacu display non-aggressive, opportunistic focused on plant dispersal rather than predation. Ecologically, pacu serve as vital seed dispersers by ingesting fruits and excreting intact viable seeds downstream, facilitating forest regeneration across Amazonian and floodplains; for instance, P. mesopotamicus disperses seeds of at least 43 plant species, including palms like Bactris glaucescens, with larger individuals passing more intact propagules. This hydrochorous dispersal enhances plant recruitment in dynamic ecosystems, underscoring pacu's keystone role in maintenance. Dietary composition varies seasonally, with higher intake of fruits and during the wet when riparian trees contribute abundant allochthonous resources, shifting to greater reliance on , , and in the as connectivity decreases. These shifts reflect adaptive responses to resource availability, ensuring nutritional balance amid fluctuating hydrological conditions.

Reproduction and life cycle

Pacu species, such as Piaractus mesopotamicus, reach at 2 to 3 years of age and a length of approximately 35 cm, though this varies slightly by sex and environmental conditions. Females generally mature at slightly larger sizes than males, with all individuals typically reproductive by 44 cm in length. Reproduction is seasonal and tied to hydrological cycles, with adults undertaking upstream migrations to areas during the rising waters of the rainy season (October to March in the River Basin). Spawning involves total release of eggs, which females scatter externally over submerged ; ranges from 64,000 to nearly 2 million eggs per female, positively correlated with body size. Fertilization is external, and there is no , classifying pacu as nonguarding brood hiders. Eggs are adhesive and develop rapidly, hatching in 18 to 19 hours at 26.5°C, with optimal temperatures for embryonic development spanning 26 to 30°C. Newly hatched larvae measure about 3.2 mm in standard length and initially rely on a for before transitioning to feeding on . Hatching success is high under natural conditions but sensitive to oxygen levels below 4 mg/L. The life cycle progresses through distinct stages: a planktonic larval phase lasting several days, during which larvae disperse and feed on microorganisms; a juvenile stage characterized by schooling behavior and a shift from zooplanktivory to herbivory on fruits, seeds, and ; and an adult stage marked by migratory breeding patterns and larger-scale movements. Growth rates during the juvenile phase influence the timing of maturity, with faster growth in nutrient-rich floodplains accelerating progression to reproductive adulthood. Reproductive success depends on environmental cues, including water level fluctuations that trigger migrations and spawning, as well as temperature regimes supporting egg viability. Hydropower dams, such as those on the Madeira River, disrupt these migrations by altering flood pulses and blocking access to spawning grounds, thereby reducing reproductive output.

Habitat requirements

Pacu species primarily inhabit slow-moving rivers, expansive floodplains, and associated lakes, where water temperatures typically range from 24 to 30°C and pH levels fall between 5.5 and 7.5. These conditions support their physiological needs, including optimal growth and metabolic functions. Additionally, pacu demonstrate notable tolerance to low dissolved oxygen environments, with species such as Colossoma macropomum capable of supplemental aerial respiration through their highly vascularized intestine, allowing survival in hypoxic floodplain waters during low-flow periods. Within these aquatic systems, pacu favor specific microhabitats that enhance , refuge, and . They often congregate near seasonally flooded forests, where falling fruits and provide essential food resources, and seek deep channels as protective refuges from predators during high-water phases. Vegetated shallows, rich in aquatic plants and marginal cover, serve as critical sites for spawning, particularly during rising water levels when adults migrate upstream to release eggs in protected, nutrient-laden areas. Their affinity for these vegetated zones also briefly aligns with dietary reliance on vegetation, facilitating access to seasonal plant matter. Pacu exhibit varying tolerance limits to environmental stressors, including the ability to endure seasonal fluctuations by retreating to deeper, water bodies rather than aestivating. However, they show sensitivity to anthropogenic disturbances such as from agricultural runoff and increased , which can clog gills, reduce respiratory efficiency, and elevate stress responses in affected populations. Habitat preferences differ among species, with Amazonian pacu like Colossoma macropomum often favoring blackwater rivers—characterized by acidic, tea-stained conditions from decaying vegetation—where individuals develop darker pigmentation for , in contrast to lighter forms in nutrient-rich whitewater rivers. These variations reflect adaptations to distinct water chemistries, with blackwater species thriving in low-conductivity, oligotrophic environments and whitewater ones exploiting higher productivity in sediment-laden flows. Pacu populations are highly dependent on climate-driven flood pulses, which annually inundate floodplains and connect isolated habitats, enabling migration, , and access to productive feeding grounds that sustain their . Disruptions to these pulses, such as altered rainfall patterns, can fragment habitats and limit connectivity, underscoring their reliance on predictable seasonal for long-term viability.

Geographic distribution

Native range

Pacu species are native to the tropical and subtropical river basins of , with their primary distributions centered in the Amazon, , Essequibo, and Paraná-Paraguay systems. These basins collectively span a broad geographic area across countries including , , , , , , , and . Specific species exhibit distinct ranges within this overall distribution; for instance, Colossoma macropomum (tambaqui) is widespread across the in , , , , , and , while Piaractus mesopotamicus (small-scaled pacu) is restricted to the basin, including the Paraguay and Paraná rivers in , , , , and . Similarly, Piaractus brachypomus (red-bellied pacu) occurs in the Amazon and basins of , , , , , and . Prior to widespread human development, pacu occupied extensive, interconnected lowland habitats from approximately 8°N to 25°S and up to 500 m , facilitating broad migratory patterns across floodplains and channels. Since the 1970s, however, the proliferation of has led to significant , isolating populations and contracting the effective range of migratory species like pacu by blocking upstream access and altering dynamics. Within these basins, pacu diversity is highest in biodiversity hotspots such as the seasonally flooded igapó (blackwater) and várzea () forests, where nutrient-rich conditions support dense populations.

Introduced and invasive populations

Pacu species, particularly Piaractus brachypomus and Colossoma macropomum, have been introduced to multiple continents outside their native Amazon and basins, mainly via human-mediated pathways associated with ornamental and food production interests. In the United States, introductions began in the mid-20th century through the aquarium trade, with the first documented record of P. brachypomus occurring in in , likely from pet releases or escapes from nearby fish farms. Similarly, C. macropomum has been present in since at least the , establishing self-sustaining populations in warm subtropical canals and estuarine systems like Charlotte Harbor, where intensive sampling from 1989 to 2007 confirmed their persistence and reproduction. In , pacu introductions date to the late , primarily from aquarium discards into ponds and rivers, with early records in in 2001 and isolated captures in France's River in 2013. These events reflect sporadic releases rather than intentional stocking, and no self-sustaining populations have established due to unsuitable cold winters, though survival has been noted in warm-water industrial effluents. A similar pattern occurred in in 2013, where a single P. brachypomus was caught, highlighting the role of pet trade but failure to colonize. Asia saw pacu introductions for aquaculture starting in the 1970s, with P. brachypomus and related species stocked in the , , , , and to bolster food production in freshwater systems. These efforts led to establishment in reservoirs and connected riverine habitats across , where escapes from farms facilitated naturalization; for instance, viable populations now occur in Philippine lakes and Indonesian ponds, supported by the species' adaptability to tropical conditions. In , recent records from the in 2024 trace back to similar aquaculture origins. In , P. brachypomus was intentionally introduced to in 1994 to the River basin and in 1997 to the Ramu River, sourced from Malaysian farms, as a response to of native species and to provide a new protein source. These releases, part of broader exotic programs dating to 1949, resulted in successful establishment in PNG's lowland rivers, with the species now reproducing and contributing to local fisheries. The dominant pathways for pacu introductions worldwide are releases of unwanted aquarium specimens and escapes from intensive operations, with recent 2020s detections in southern U.S. states like (2020) and (2024) linked to pet abandonments in warmer southern waters. Once introduced, pacu spread via interconnected waterways, leveraging their broad thermal tolerance—chronic exposure limits of 16.5°C to 35°C—which enables persistence in subtropical and tropical environments but restricts colonization in temperate zones with prolonged cold.

Human uses and interactions

Aquaculture and commercial fisheries

Pacu species, particularly Colossoma macropomum (), support significant native fisheries in the , where artisanal fishers employ gillnets to target migrating schools during seasonal flood pulses. Historical capture yields for C. macropomum peaked at approximately 53,800 tons in 2012, with declines due to reducing yields and shifting pressure toward to meet demand. Aquaculture development for pacu began in Brazil during the 1970s, building on early into induced spawning to overcome the species' reliance on natural cues for . Production systems include semi-intensive earthen ponds yielding up to 10 tons per annually and culture in rivers, with feeds centered on plant-based ingredients like soybeans and matter to align with the fish's herbivorous diet. Global output for pacu species, primarily from , reached 142,000 tons in 2016. As of 2023, produced approximately 113,600 tons of tambaqui, with native species including pacu totaling 263,479 tons, reflecting continued growth. In 2023, Brazil's total production reached 887,029 tons, and farmed fish exports rose 102% in volume to 13,792 tons in 2024. Economically, pacu serves as a vital protein source in , supporting and generating revenue through domestic markets and emerging exports of value-added products like pacu ribs to the and . However, declining wild stocks from pose ongoing challenges, necessitating to sustain both capture and farmed sectors. Key farming techniques include hormonal induction using analogs like buserelin acetate or GnRH to trigger spawning in captivity, enabling multiple batches per season and high fecundity rates. systems, often integrating pacu with , enhance productivity by utilizing different trophic levels and have become common in Brazilian operations. Post-2020, sustainability certifications such as those from the Aquaculture Stewardship Council have gained traction among Brazilian producers, promoting reduced environmental impacts and traceability. Pacu's nutritional profile features elevated levels of omega-3 fatty acids, beneficial for cardiovascular health, alongside low mercury accumulation due to its primarily herbivorous feeding habits that limit exposure to contaminants higher in the food chain.

Aquarium trade

Juvenile specimens of the black pacu (Colossoma macropomum) and red-bellied pacu (Piaractus brachypomus) are among the most popular species in the aquarium trade, valued for their striking silver or reddish body colors and prominent, human-like teeth that evoke comparisons to piranhas despite their herbivorous nature. These species are typically imported as small juveniles measuring 2-3 inches (5-8 cm), appealing to hobbyists seeking exotic, peaceful community fish that can initially coexist with other species. Keeping pacu requires substantial resources due to their rapid growth and specific needs; for red-bellied pacu, adults up to 60 cm (24 inches) demand a minimum size of 1,000 liters (approximately 264 gallons), while black pacu up to 108 cm require much larger setups such as 2,000+ liters or ponds, along with powerful filtration to handle waste from their active swimming and . A vegetarian diet consisting of blanched vegetables such as , peas, , and , supplemented with fruits like apples and high-quality pellets, supports their health, while water temperatures must be maintained between 23-28°C (73-82°F) to mimic their Amazonian origins. However, their fast growth often leads to rehoming challenges, as many owners underestimate the space requirements, resulting in fish being donated to public aquariums or, more problematically, released into local waterways. The aquarium trade in pacu experienced a surge in the 1990s within the hobbyist market, driven by imports of juveniles marketed as "vegetarian ," though specific volume data for pacu remains limited amid broader ornamental fish imports exceeding tens of millions annually during that period. Today, much of the trade relies on sustainable sourcing from South American and Far Eastern farms, where pacu are also raised for food production, reducing pressure on wild populations. Regulations have tightened in response to invasive risks; while imports are permitted, releases are banned in and many states, with pacu classified as a conditional under Florida Fish and Wildlife Conservation Commission rules prohibiting the possession or release of non-native fish without permits to prevent ecological harm. Similar restrictions apply in the under Council Regulation (EC) No 708/2007, which controls introductions of non-native aquatic to mitigate pathways from the pet trade. Challenges in the pacu trade include high mortality rates from improper tank sizing, where juveniles in undersized setups suffer , stress, and organ failure, exacerbating ethical concerns over promoting "tankbuster" that outgrow home aquariums. Aquarists often face difficulties in providing the necessary setups recommended for mature specimens, leading to welfare issues and unintended contributions to invasive populations through releases. Efforts to address these include campaigns by organizations like the Ornamental Fish International advocating for better on to promote responsible ownership.

Recreational fishing

Recreational fishing for pacu, especially species like the (Colossoma macropomum), attracts anglers seeking challenging sport in freshwater environments due to the fish's robust build and potential for large specimens exceeding 30 kg. These fish are targeted using specialized methods that exploit their herbivorous diet, including with lures designed to mimic fruits such as berries or nuts, often presented on light tackle to enhance the fight. Anglers also use natural baits like fruits or bread on sturdy rods and reels with strong lines to handle the pacu's powerful runs. provides another technique in shallow, clear waters where visibility allows for accurate shots, particularly in riverine habitats. Pacu are renowned as strong fighters on light tackle, capable of sustained battles that test an angler's skill without requiring heavy gear. Prime locations for pacu span native Amazonian rivers and introduced populations elsewhere. In the , guided trips from lodges along rivers like the Sécure or Madre de Dios target trophy in slow-moving pools and floodplains, offering immersive experiences in remote settings. , introduced pacu thrive in Florida's canals, ponds, and slower waterways, providing accessible urban fishing opportunities for locals encountering these exotics in places like North Beach or canals. Tournaments and records highlight pacu's status as a premier sport fish. The International Game Fish Association (IGFA) recognizes a rod-and-reel world record of 37 kg (81 lb 9 oz) for C. macropomum, caught in Peru in 2013, while an alternate methods record stands at 45 kg (99 lb 3 oz) from Brazil in 2015. In Brazil, annual sport fishing events such as those in Foz do Iguaçu and the São Paulo Fishing Tournament feature pacu categories, drawing competitors to rivers rich in the species. The Bowfishing Association of America lists a pacu record of 39.90 lbs (18.1 kg) from 2019, underscoring the species' appeal across angling disciplines. Pacu's appeal lies in their impressive size potential—up to 100 cm and 45 kg—and acrobatic fights, where hooked fish leap and surge, evoking comparisons to permit in jungle settings. operations in the Amazon promote catch-and-release practices with barbless hooks and fly-only zones to sustain populations while enhancing the adventure of targeting wary, surface-sipping fish. Regulations vary by region to balance recreation with sustainability. In native Brazilian waters, must measure at least 55 cm to be legally harvested, with daily bag limits and closed seasons from November to March to prevent overharvest during spawning. In invasive areas like , no size or bag limits apply to pacu, and the Florida Fish and Wildlife Conservation Commission encourages their removal to mitigate ecological risks.

Environmental and conservation issues

Ecological impacts as invasives

Introduced pacu species, particularly Piaractus brachypomus, pose significant ecological risks in non-native ecosystems through resource competition and dietary shifts that disrupt local food webs. As primarily herbivorous fish with opportunistic feeding habits, they outcompete native herbivores for limited vegetation, such as aquatic plants and fruits, potentially reducing food availability for indigenous species like floodplain fishes in tropical rivers. In the Sepik-Ramu River Basin of Papua New Guinea, where P. brachypomus was introduced in the 1990s for aquaculture, the species has exhibited a marked diet shift from its native frugivorous preferences to consuming higher volumes of fish remains (49.94%) and aquatic plants (26.89%), exacerbating competition with native herbivores and altering trophic dynamics. Habitat alteration by invasive pacu primarily stems from of aquatic and , which inhibits the of native plants essential for structure. By voraciously consuming submerged and emergent plants, pacu can degrade littoral zones critical for and invertebrate habitats, leading to reduced in affected waterways. Local reports from the Sepik-Ramu Basin indicate declines in native populations attributed to this vegetation loss, highlighting how pacu's feeding behavior transforms floodplain into less diverse habitats. Additionally, their consumption of seeds (approximately 9.89% of diet in introduced PNG populations) may prevent the regeneration of riparian , further destabilizing riverine environments. Predation effects from pacu are generally rare but notable in juveniles and under resource scarcity, where they may target small native fishes, eggs, or fry, contributing to recruitment failures in invaded systems. In , introduced P. brachypomus has been observed killing local and decimating eggs and fry, causing ecological imbalances that extend to broader community shifts. Hybridization risks with native characins remain low outside due to taxonomic barriers, though potential in regions with similar cypriniform fishes could complicate local assemblages if populations establish. Case studies underscore these impacts, particularly in PNG's Sepik-Ramu rivers, where introductions since the 1990s have led to observable ecosystem shifts, including reported native declines and altered cover. In the United States, sporadic captures of pacu in Florida's waterways since the suggest potential for similar effects if establishment occurs, with their voracious herbivory threatening to mirror PNG disruptions in subtropical systems. Recent assessments, including U.S. Fish and Wildlife Service evaluations, classify P. brachypomus as posing an uncertain but elevated risk due to its biological traits and documented impacts abroad, emphasizing the need for monitoring in high-climate-match areas like the U.S. Southeast.

Conservation status and threats

The conservation status of pacu species varies across genera, reflecting differing levels of threat in their native South American ranges. Colossoma macropomum, commonly known as tambaqui, is classified as Near Threatened on the IUCN Red List due primarily to ongoing overfishing and the construction of hydroelectric dams that disrupt migratory patterns. , the red-bellied pacu, holds a Least Concern status, though local populations show signs of decline from habitat alteration and exploitation. In contrast, Piaractus mesopotamicus, or the silver pacu, is assessed as Near Threatened, driven by similar pressures including river damming and intensive fishing in the Paraná-Paraguay basin. Major threats to pacu in their native habitats stem from human activities that degrade aquatic ecosystems. in the has resulted in approximately 20% loss of forest cover since the 1970s, leading to increased , warmer river temperatures, and reduced connectivity essential for pacu and spawning. Hydroelectric dams, such as Brazil's Belo Monte project operational since 2015, block upstream migrations critical for reproduction, causing declines in abundance downstream by up to 16% in lotic environments. from introduces mercury into rivers, where it bioaccumulates in tissues, posing risks to pacu populations and their predators. Overexploitation through commercial and artisanal fisheries has led to substantial reductions in wild pacu catches due to unsustainable harvesting. exacerbates these pressures by altering seasonal flood cycles, which delays spawning in flood-dependent species like C. macropomum and reduces larval survival during prolonged droughts; extreme droughts in 2023-2024 have caused mass die-offs, further threatening populations. Conservation efforts focus on mitigating these threats through habitat protection and population enhancement. In , protected areas within the Amazon, such as the Mamirauá Sustainable Development Reserve, safeguard migratory routes and breeding grounds for pacu . Restocking programs, including genetic monitoring of broodstock for Piaractus mesopotamicus in rivers like the Tietê and Grande, aim to bolster depleted stocks and support sustainable fisheries. While pacu are not currently listed under , national regulations in enforce fishing quotas and seasonal closures to prevent further declines.

Myths and cultural references

Testicle-biting misconception

The misconception that deliberately target and bite testicles originated from unverified reports in around 2011, where two fishermen allegedly bled to death after genital injuries attributed to the invasive in the River. These incidents, later amplified in media, were likely misattributions; no documented confirms as the cause, and experts suggest the injuries may have resulted from other factors, such as or unrelated trauma during wading or fishing in remote areas. The 's -like , adapted for cracking hard nuts and seeds, further fueled rumors by drawing superficial comparisons to anatomy, though this is a coincidental evolutionary trait unrelated to predatory behavior toward people. Sensationalized headlines in the 2010s propelled the myth globally, with UK tabloids like the Daily Mail and Mirror dubbing the pacu the "ball-cutter" or "nutcracker" following its introduction as an invasive species in non-native waters, often conflating it with aggressive piranha attacks. Coverage peaked in 2013 after pacu sightings in Scandinavian waters prompted hoax warnings about nude swimmers, and continued with reports of captures in U.S. lakes, blending fact with exaggeration to evoke fear of a "killer fish." This media frenzy confused the pacu's primarily herbivorous nature—feeding on fruits, nuts, and vegetation—with carnivorous threats, ignoring that documented human interactions rarely involve unprovoked aggression. Scientific consensus refutes the notion of targeted predation, emphasizing the pacu's vegetarian diet and docile temperament in , where bites on humans are exceedingly rare and typically defensive responses to handling or threat. biologists, including those studying invasive populations, confirm no verified cases of fatal or genital-specific attacks by pacu exist, attributing the legend to and rather than biology. Despite this, the persists culturally through viral memes, online forums, and documentaries like the 2011 River Monsters episode featuring host investigating PNG rumors, which inadvertently amplified the tale into the 2020s via shares and content. In reality, any risks from pacu to humans stem from accidental encounters, such as hooks during causing injury when fish are reeled in, or minor nips from territorial displays in aquariums where stressed individuals defend space. These incidents are non-lethal and avoidable with proper handling, underscoring that pacu pose no inherent danger to swimmers or fishermen beyond standard fishing hazards.

Role in folklore and media

In indigenous Amazonian folklore, the pacu features in tales collected from Brazilian communities, where it appears as a prized catch in stories of familial expeditions, symbolizing abundance and the between humans and the river's bounty. For instance, in retellings, a father and son venture to the waters, with the boy eagerly landing smaller pacu while the elder hauls larger specimens, underscoring themes of generational knowledge and the river's generosity. The name "pacu" itself derives from the Old Tupi word paku, reflecting its role as a swift consumer of fruits, which ties into broader Tupi-Guarani narratives of natural plenty in the floodplains. In modern media, the pacu has been portrayed in documentaries emphasizing its ecological significance in the Amazon. BBC programs, such as the "Andes to Amazon" series episode "Fish and Fruit," depict pacu feeding on fallen fruits during the , illustrating their vital function in across flooded forests and highlighting the interconnectedness of aquatic and terrestrial ecosystems. These representations often frame the pacu as an exotic, non-predatory counterpart to , showcasing Amazonian rather than danger. The pacu also appears in video games and as an exotic freshwater species. In Megaquarium, a game focused on aquarium management, the pacu is introduced as a large, herbivorous relative of , unlocked at higher levels to educate players on its real-world traits and care requirements. Similarly, in virtual reality titles like Real VR Fishing, the red-bellied pacu serves as a catchable species in Amazon-inspired environments, promoting awareness of diversity through gameplay. In , the pacu gained traction on in the 2010s due to its human-like teeth, sparking viral posts and memes about unusual invasive catches in North American waters. For example, a 2015 incident in , where a pacu was pulled from a local lake, exploded online with thousands of shares, often shared for its novelty as a "smiling" Amazon import likely dumped from the aquarium trade. These trends, amplified on platforms like and , have boosted public curiosity about exotic without delving into sensationalism. Ecotourism promotions in further elevate the pacu, featuring it in packages for sustainable in the Pantanal and Amazon, where anglers target it as a symbol of the region's vibrant fisheries. Symbolically, the pacu represents Amazonian in environmental campaigns, particularly its role in forest regeneration. Organizations highlight how pacu consume and disperse seeds from over 20 tree , traveling up to 0.5 km to plant new growth, making it a against threats; declining populations signal broader habitat loss. In the , news coverage of pacu invasives in places like and U.S. lakes has raised local awareness of ecological risks, with reports from noting captures in reservoirs that prompt discussions on pet trade regulations and native protection. In , described a new of pacu relative, Colossoma sauroni, named after the "Lord of the Rings" villain due to its prominent teeth, drawing media attention to Amazonian and fictional parallels.

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