Geographic Range
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 hobbyistsâ 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
- neotropical
Habitat
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.
- Habitat Regions
- tropical
- freshwater
- Aquatic Biomes
- rivers and streams
Physical Description
Red-bellied pacu are often confused with other pacu (
Piaractus mesopotamicus
,
Colossoma macropomum
) or piranha (
Serrasalmus 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 âthey
will grow to fit their environmentâ 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.
- Other Physical Features
- ectothermic
- heterothermic
- bilateral symmetry
- Sexual Dimorphism
- sexes alike
Development
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
Reproduction
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 âknockingâ 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.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- fertilization
- 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
-
protecting
Lifespan/Longevity
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.
Behavior
In native environments, red-bellied pacu are shoaling fish that may become more independent
with age. A pacuâs entire life is characterized by annual cycles corresponding to
the rainy and dry seasons. They migrate upstream during the months of June through
October and then, in response to the first rains of the wet season, start to spawn
from November to February.
All pacu species are known for being able to adjust to unfavorable environmental conditions,
such as depleted oxygen levels. Behavioral responses to these conditions include spending
greater amounts of time near the surface, increased movement, and protrusion of the
lower lip, all of which facilitate the use of surface water in respiration.
- Key Behaviors
- natatorial
- diurnal
- motile
- migratory
- territorial
- social
Home Range
Information regarding the home range size of this and other pacu species is currently
lacking. Though young individuals form shoals and are peaceful to conspecifics, observations
of aquarium specimens have indicated that aggression and territoriality increase as
the fish age.
Communication and Perception
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.
- Other Communication Modes
- mimicry
- pheromones
- vibrations
- Perception Channels
- visual
- tactile
- acoustic
- vibrations
- chemical
Food Habits
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 âbite
eventsâ, 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
Predation
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.
Ecosystem Roles
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)
Economic Importance for Humans: Positive
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.
Economic Importance for Humans: Negative
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
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
Conservation Status
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.
Additional Links
Contributors
Blake Hintz (author), Radford University, Karen Powers (editor), Radford University, Christine Small (editor), Radford University, Jeremy Wright (editor), University of Michigan-Ann Arbor.
- oriental
-
found in the oriental region of the world. In other words, India and southeast Asia.
- introduced
-
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
- Neotropical
-
living in the southern part of the New World. In other words, Central and South America.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- freshwater
-
mainly lives in water that is not salty.
- marsh
-
marshes are wetland areas often dominated by grasses and reeds.
- swamp
-
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- heterothermic
-
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
- bilateral symmetry
-
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- indeterminate growth
-
Animals with indeterminate growth continue to grow throughout their lives.
- polygynandrous
-
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
- iteroparous
-
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- fertilization
-
union of egg and spermatozoan
- external fertilization
-
fertilization takes place outside the female's body
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- natatorial
-
specialized for swimming
- diurnal
-
- active during the day, 2. lasting for one day.
- motile
-
having the capacity to move from one place to another.
- migratory
-
makes seasonal movements between breeding and wintering grounds
- territorial
-
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
- social
-
associates with others of its species; forms social groups.
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- mimicry
-
imitates a communication signal or appearance of another kind of organism
- pheromones
-
chemicals released into air or water that are detected by and responded to by other animals of the same species
- vibrations
-
movements of a hard surface that are produced by animals as signals to others
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- vibrations
-
movements of a hard surface that are produced by animals as signals to others
- chemical
-
uses smells or other chemicals to communicate
- detritus
-
particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).
- pet trade
-
the business of buying and selling animals for people to keep in their homes as pets.
- food
-
A substance that provides both nutrients and energy to a living thing.
- carnivore
-
an animal that mainly eats meat
- piscivore
-
an animal that mainly eats fish
- insectivore
-
An animal that eats mainly insects or spiders.
- molluscivore
-
eats mollusks, members of Phylum Mollusca
- herbivore
-
An animal that eats mainly plants or parts of plants.
- frugivore
-
an animal that mainly eats fruit
- granivore
-
an animal that mainly eats seeds
- omnivore
-
an animal that mainly eats all kinds of things, including plants and animals
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