Taxonomy & naming
Arapaima mapae was described by the French zoologist Achille Valenciennes in 1847, based on a single specimen — the holotype, now held at the Muséum national d'Histoire naturelle in Paris (MNHN A-8836) — collected from Lago Mapa, a lake now known as Lago do Amapá in Amapá State, Brazil. The species epithet mapae directly references that type locality. It belongs to the family Arapaimidae within the order Osteoglossiformes, the bonytongues: one of the oldest surviving branches of the ray-finned fish tree, named for the toothed bone on the floor of the mouth that works against toothed plates on the roof to grip and crush prey. Osteoglossiformes is a scattered, deep-time radiation spread today across South America, Africa, Southeast Asia and Australasia — arapaima and arowanas on one side of the Atlantic, butterflyfish and the electric Gymnarchus in Africa, arowanas and saratoga across Asia and Australasia on the other. Arapaima mapae is a South American member of that radiation, and the smallest-range one of the lot.
For most of the twentieth century the genus Arapaima was treated as containing a single species, A. gigas, with Valenciennes's mapae and several other described names folded into it as synonyms. A 2013 taxonomic review by Donald Stewart re-examined the genus and revalidated several of those older names as distinct species — among them A. mapae, A. agassizii and A. leptosoma alongside A. gigas — based on differences in scale and fin-ray characters across the type material. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) currently treats Arapaima mapae as a valid, distinct species on that basis. It is worth being direct about what that means in practice: the species was defined from one museum specimen collected nearly two centuries ago, and no confirmed additional collection has followed it, so its validity rests on comparative morphology of old material rather than on a body of field observation.
Morphology
The only concrete morphological data point for Arapaima mapae is its holotype: a specimen measuring about 79.9 in in standard length. FishBase records that figure as SL rather than total length, which means the fish's actual total length — including the tail fin — would have been somewhat greater; the US Fish & Wildlife Service's ecological risk assessment separately gives an approximate maximum around six feet (roughly 70.9–78.7 in), broadly consistent with a large adult arapaima. Beyond that single measurement, no detailed morphological description of colour pattern, scale counts or fin proportions specific to A. mapae is available in the sources consulted here.
What can be said comes from the shared biology of the genus, which A. mapae almost certainly follows in broad strokes even though it has not been directly documented in this species: an elongated, torpedo-shaped body covered in large, thick, bony scales, a broad flattened head, and — the genus's defining trait — a swim bladder modified into a lung-like, heavily vascularised air-breathing organ. Reduced gill surface area relative to body size makes adult arapaima obligate air-breathers that must periodically rise and gulp air at the surface or drown, regardless of how much oxygen is dissolved in the water below. Whether A. mapae shows the coppery-red tail colouration reported in other Arapaima species has not been documented from the type material available to this account.
Habitat
Arapaima mapae is known only from Lago do Amapá, a floodplain (várzea) lake in Amapá State, in the far north of the Brazilian Amazon near the border with French Guiana — an extremely restricted, single-water-body range by any measure. No systematic environmental data specific to this lake or this species — temperature, pH, seasonal water-level pattern — appears in the sources available here, so anything more precise would be guesswork.
What is reasonably inferred, and consistent with every other member of the genus, is that Lago do Amapá is the same kind of habitat other arapaima occupy across Amazonia: a warm, humid-tropical floodplain lake subject to the basin's dry-season/wet-season flood pulse, often running low in dissolved oxygen as water levels fall and vegetation decomposes in warm, still water — precisely the condition that favours an obligate air-breathing fish. Beyond that genus-level expectation, the habitat of A. mapae specifically has not been re-surveyed since the nineteenth century.
Feeding
No feeding data specific to Arapaima mapae has been documented; the species is known from a single preserved specimen, not from field observation of live animals. What can be said is inference from the genus: Arapaima species are carnivorous ambush predators that feed heavily on fish, striking from cover with a fast, short-range lunge, and rounding out the diet with crustaceans and other prey encountered in the water column.
Whether A. mapae hunts identically — same prey spectrum, same seasonal shifts as floodwaters rise and fall — is a reasonable extrapolation from its close relatives rather than a directly confirmed fact. This account flags that distinction rather than presenting genus-level habits as species-specific certainty.
Mating
No breeding behaviour has been documented for Arapaima mapae itself. The genus as a whole, however, breeds in a well-characterised way that is reasonable to expect this species shares: pairs form during the low-water season and the male excavates a shallow nest depression in soft substrate, on the order of 19.7–23.6 in across and 5.9–7.9 in deep, in shallow water near cover, timed so the resulting fry emerge into the food-rich conditions of the rising flood.
The female then lays her eggs into the nest for the male to fertilise. As with the rest of the genus's biology reported here, this is a description of how Arapaima breeds in general rather than a confirmed account of A. mapae specifically — no nest, spawning event or juvenile of this species appears to have ever been documented in the wild.
Breeding
Again extrapolating from the genus rather than from direct observation of A. mapae: Arapaima species that have been studied show intensive, biparental-leaning care, with the male guarding the nest, eggs and free-swimming fry, which shoal in a tight ball close around the guarding parent's head for protection as they grow. Other Arapaima species are farmed at real scale for food across Brazil and Peru, exploiting exactly this parental-care biology and the genus's tolerance for dense, low-oxygen pond stocking.
There is no indication in the sources consulted here that Arapaima mapae itself has ever been bred, farmed, or even re-collected since its 1837 holotype — so while its congeners' breeding biology is well characterised, whether this particular species follows the pattern exactly, and whether it could ever be propagated given how little is known of its remaining wild population (if any survives), are both open questions.
In the aquarium
Arapaima mapae has no place in the home aquarium hobby, and in practice it is essentially unavailable — this is not a species offered in the aquarium trade, and given that it is known from a single 1837 museum specimen with no confirmed collections since, there is no credible supply chain that could honestly claim to be selling true A. mapae rather than a generically labelled young arapaima of uncertain species. Fish sold in the trade as "arapaima" are overwhelmingly farmed A. gigas or unspecified Arapaima species, not this narrow Amapá endemic.
The broader size-trap warning that applies to the genus is worth stating plainly regardless: Arapaima species grow to roughly two to three metres and hundreds of kilograms, require unobstructed surface access at all times because they must gulp air or drown, and belong to public aquaria, research institutions and dedicated aquaculture ponds — never to a private tank. Even setting aside its extreme rarity, nothing about A. mapae's genus-level biology suggests it would be any different.
Conservation
The IUCN Red List assesses Arapaima mapae as Data Deficient, an assessment last dated to December 2020. That status reflects the honest state of knowledge: a species defined from a single specimen collected in 1837, with no confirmed re-collection since, and an extremely restricted range confined to one floodplain lake. It is genuinely unknown whether A. mapae still survives in Lago do Amapá, whether it has been extirpated, or whether it was ever more than locally common to begin with — sources reviewed here note that some non-IUCN assessments have floated Vulnerable as a plausible status given the restricted range and general threats facing Amazon fish, but no confirmed current data supports a more precise call than Data Deficient.
The general pressures facing Amazon floodplain fish — overfishing (arapaima are unusually easy to locate and harpoon because they must surface to breathe), habitat degradation, and pollution — are the same pressures that would threaten A. mapae if a surviving population exists. Its congener Arapaima gigas is regulated under CITES Appendix II and heavily farmed for food; whether that trade regulation meaningfully extends to or protects A. mapae specifically is not established in the sources available here. Given how little is confirmed about this species, the most defensible statement is the plain one: its status is genuinely unresolved, not confirmed as safe.