FishFreshwaterExpert
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Arapaima (Pirarucu)
Arapaima gigas
The Amazonian Leviathan (Up to 3 meters / 10 feet). One of the largest true freshwater fishes in the world, wrapped in bullet-proof scales rimmed with fiery red. It is a strictly 'monster pond' or public aquarium animal. Selling a cute 6-inch baby to a home aquarist is highly unethical, as it grows at an explosive rate and possesses the brute force to shatter standard glass aquariums to pieces in a panic, dooming the fish to a tragic, confined death.
Water Temperature
25 - 29 °C
pH Value
6 - 7.5
Water type
Freshwater
Tank level
Surface and middle
Adult size
300 cm
Minimum tank volume
>= 500 L
Minimum group
>= 1
GH
4 - 15 dGH
KH
2 - 7 dKH
TDS
80 - 295 ppm
Conductivity
125 - 461 uS/cm
Species description
Geographical Origin and Habitat: The giant of the Amazon and Essequibo basin. Inhabits flooded forests (varzea), rivers and marginal lakes. Thrives in hypoxic (oxygen-poor) waters of calm rivers, coming up to breathe air.
Taxonomy and Morphology: Arapaima / Pirarucu (Arapaima gigas). One of the largest freshwater fish in the world (exceeds 3 meters / 10 feet). It is a living fossil (Arapaimidae) equipped with immense armored scales and a massive mouth bristling with crushing teeth.
Social Behavior: Supreme and undisputed hunter. Breathes atmospheric air through a modified swim bladder similar to a lung, emerging noisily (gulp) every 10-15 minutes. Relatively tolerant towards immense fish that do not fit in its mouth.
Coloration and Sexual Dimorphism: Bronze-gray as juveniles, upon maturing they develop spectacular fiery red scales (Arapaima = "Red Fish" in Tupi) on the rear half of the body. There is no evident sexual dimorphism outside the breeding season.
Care, breeding and tankmates
Aquarium Setup: ABSOLUTELY UNSUITABLE FOR DOMESTIC AQUARIUM KEEPING. Exclusively intended for zoos, public mega-aquariums or huge heated tropical ponds of tens of thousands of liters/gallons. Needs reinforced anti-jump nets.
Diet and Feeding: Apocalyptic carnivorous predator. Feeds on whole fish, frogs, crustaceans and birds that fall into the water. In captivity it is fed with tilapia fillets, floating pellets for giant Koi and frogs.
Water Quality: Extremely resilient, especially to oxygen scarcity, but its impressive organic load (feces) will quickly turn any tank not equipped with gigantic industrial filters into a sewer.
Compatibility and Cohabitation: Everything under 40-50 cm (16-20 inches) is instant food. Cohabits in public mega-systems with large Pacu (Colossoma), Phractocephalus hemioliopterus (Redtail Catfish) and giant freshwater Stingrays (Potamotrygon).
Aquarium Breeding: Unthinkable in home aquariums. Reproduces by digging enormous holes in the sandy bottoms during the dry season. The male is a model parent who guides the fry in a group, keeping them close to his dark head.
Risks and Diseases: Endangered species protected by CITES. Its reckless sale as a 10 cm (4 inch) puppy ("cute monster") invariably causes the death of the fish in cramped tanks or the collapse of home glass due to impacts as an adult.
Geographic Origin and Distribution
The giant of the Amazon and Essequibo basin. Inhabits flooded forests (varzea), rivers and marginal lakes. Thrives in hypoxic (oxygen-poor) waters of calm rivers, coming up to breathe air.
Origin
Amazon, Orinoco, and Guianas
Fish profile
- Temperament
- Semi-aggressive
- The temperament of the arapaima is predatory yet generally peaceful toward species that are too large to be considered food. They are not highly aggressive by nature but are formidable apex predators that will consume any tankmate they can swallow. Adult specimens can become territorial toward conspecifics if kept in confined spaces, leading to severe physical damage. Startled individuals can exhibit sudden, explosive bursts of speed, which can cause significant damage to the tank and themselves.
- Diet
- Omnivore
- Arapaima gigas is a strict carnivore with a voracious appetite that reflects its rapid growth rate. In the wild, their diet consists of fish, crustaceans, insects, and occasional land animals like birds or small mammals. Captive specimens should be fed a varied diet of whole fish, shrimp, crabs, and high-quality, high-protein floating carnivore pellets. Live feeder fish should generally be avoided to minimize the risk of introducing parasites or disease into the system.
- Life expectancy
- 15-20 years
- Under optimal care, the lifespan of Arapaima gigas in captivity ranges from fifteen to twenty years, with some specimens exceeding this in large public aquariums. Reaching this longevity requires maintaining pristine water quality, a balanced diet, and an environment large enough to support their growth. Poor water conditions, inadequate nutrition, or insufficient space will severely reduce their life expectancy. Providing a stable, stress-free environment is key to helping them reach their full genetic potential.
- Adult size
- 300 cm
- The catalog's scalar value is 300 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 450 cm for this species, recorded as total length (TL). The taxonomic record consulted is Arapaima gigas (v25.04); male or unsexed record. These figures are not interchangeable: the first is the profile's editorial reference, whereas the second is a published maximum under a specific measurement convention; differences among sources can reflect sex, population, life stage and measuring method.
- Sex ratio
- 1:1 ratio
- Stocking arapaima requires careful consideration since they are generally kept as solitary specimens in all but the largest public facilities. For breeding purposes, a strict 1:1 sex ratio is recommended, though forming compatible pairs is difficult due to the lack of clear sexual dimorphism. In massive, pond-like enclosures, they can sometimes be kept in small groups, provided there is enough space to prevent territorial conflict. Due to their immense size, keeping multiple adults in average captive environments is highly discouraged.
- Feeding frequency
- Twice daily
- Juvenile arapaimas are fast-growing and should be fed daily with high-protein meals to support their rapid development. As they reach sub-adult and adult sizes, the feeding frequency can be reduced to three or four times a week. Overfeeding adults must be avoided, as it can lead to obesity, fatty liver disease, and severe water quality issues. Food should be offered in controlled amounts that the fish can consume entirely within a few minutes.
- Bioload
- Extreme
- Arapaima gigas produces an extreme biological load due to its massive adult size, often exceeding two meters in length and weighing over one hundred kilograms. Standard aquarium filtration is completely inadequate, requiring commercial-grade, heavy-duty sump filtration or open pond turnover systems. Frequent, large water changes and advanced mechanical extraction are necessary to manage the huge volume of solid waste and prevent ammonia spikes. High oxygen levels must also be maintained despite their air-breathing capability, as bacteria in the biological filter require substantial dissolved oxygen.
- Flow
- Stagnant
- In their native Amazon basin, arapaimas prefer lentic habitats such as slow-moving rivers, oxbow lakes, and flooded forests. Therefore, they thrive in environments with weak to moderate water flow rather than strong currents. Gentle currents help simulate their natural habitat and allow them to swim without exerting excessive energy. Proper filtration turnover must be achieved without creating turbulent flows that could stress or exhaust these large fish.
- Jump risk
- Yes
- The jump risk for Arapaima gigas is extremely high and poses a significant danger to both the fish and its caretakers. These powerful fish can leap high out of the water, driven by their natural hunting instinct for birds and branches, or when startled. A very secure, heavy, and potentially padded cover is mandatory to prevent them from leaping out or sustaining fatal injuries upon impact. In open-top public exhibits, high barrier walls or safety netting must be installed around the perimeter.
- Reproduction
- Oviparous
- Reproduction of Arapaima gigas in captivity is exceptionally difficult and is almost exclusively achieved in large aquaculture ponds or public aquariums. They are nest-builders, with males excavating a shallow pit in sandy substrates during the dry season. The female deposits thousands of eggs, which are then fertilized and guarded diligently by both parents, particularly the male. Spawning is triggered by seasonal flooding cycles, which are very difficult to replicate in standard aquarium setups.
- Compatibility & tankmates
- Due to their massive size and predatory nature, arapaimas are only compatible with other giant, robust species that cannot be swallowed. Suitable tankmates include large catfish like Phractocephalus hemioliopterus, large pacus, and massive cichlids, provided the enclosure is enormous. Any fish small enough to fit into the arapaima's wide mouth will inevitably be consumed. Keeping them with aggressive or highly territorial species should be avoided to prevent stress and injury.
- Tank level
- Top/Middle
- Arapaima gigas is a middle-to-top dweller that actively utilizes the upper water column. As an obligate air-breather, it must regularly ascend to the surface every five to fifteen minutes to gulp air, making surface access critical. They hunt and cruise primarily in these shallower, warmer zones of the habitat. Enclosures must feature sufficient vertical space to accommodate this frequent surfacing behavior comfortably.
Scientific Parameters & Models
FishBase
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 4.5 ± 0 se
- Resilience
- Low (4.5 - 14 years)
- Generation time
- 11.1 years
- Phylogenetic uniqueness (PD50)
- 0.5469
- Bayesian Length-Weight
- a = 0.01096, b = 2.94
- VulnerabilityModerate to high vulnerability (54 / 100)
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
Related species
Recommendations grouped by close relatives, companion choices, and similar care.
