Taxonomy & naming
Sven O. Kullander and Efrem J. G. Ferreira described Apistogramma angayuara in 2005 in the open-access journal Neotropical Ichthyology (3(3):361–371) — the same paper that named its Trombetas neighbour Apistogramma salpinction. The holotype is an adult male just 1 in in standard length, registered as INPA 24058 at the Instituto Nacional de Pesquisas da Amazônia in Manaus. It and its paratypes were collected on 4 October 1985 from a stagnant pool of sand, rock and dry leaves on the right bank of the rio Trombetas, below the cachoeira (waterfall) Vira Mundo, by E. Ferreira and L. Rapp Py-Daniel.
The specific epithet is neither Latin nor Greek but Língua Geral, the Amazonian trade language descended from Tupí. Following the original description (which cites Grenand & Ferreira), angayuara is an adjective meaning skinny or thin, used here as a noun in apposition — a nod to the fish's slender build; FishBase and the ETYFish Project carry the same reading. FishBase also lists the English book-name "elongated dwarf cichlid," but that is an aggregator label rather than a settled hobby name, and the fish is referred to by its scientific name.
Kullander and Ferreira placed the species in the Apistogramma pertensis species group, and specialists have long treated it as part of the pertensis complex — closer in form to Apistogramma meinkeni than to Apistogramma pertensis itself. By the reckoning of the long-time Apistogramma authority Mike Wise (apistogramma.com), it is an atypical, aberrant member of that lineage: a rapids-dwelling rheophile with a near-microscopic body and an unusually low, even male dorsal fin, none of which fits the blackwater, leaf-litter stereotype of its relatives. The genus Apistogramma sits in the cichlid subfamily Geophaginae, the eartheater lineage. Before it had a name, the fish circulated among specialists as "Apistogramma sp. Trombetas 1" and under the code A-145.
Morphology
This is a genuinely tiny fish. The type series tops out at a 1 in male and a 1 in female in standard length, which makes Apistogramma angayuara the smallest Apistogramma described to date — smaller even than other dwarfs in the genus. The body is markedly elongate and slender, its depth only about 26–29% of standard length, exactly what the name advertises.
No live fish has ever been photographed, so its colours are known only from preserved material, where pigment fades to browns and greys. Kullander and Ferreira diagnose it by a combination of marks rather than any single flashy one: three prominent stripes of dark spots running along the sides of the abdomen, a distinct spot at the caudal-fin base, and — unusually for a male Apistogramma — a low, even dorsal fin rather than the raised crest or extended lappets many congeners carry. Internally, two postlachrymal infraorbital pores and five dentary pores help separate it from related pertensis-group species. Sexual dimorphism is presumed to follow the genus pattern — males larger, females smaller and rounder when gravid — but with both sexes capped near 1 in SL the differences are slight, and the colour of a breeding female in life is simply unknown.
Habitat
Apistogramma angayuara is endemic to Brazil and, as far as the record shows, to the upper rio Trombetas in Pará — specifically the reach around the cachoeiras Porteira and Vira Mundo, above the lower-river rapids where the Trombetas meets the Mapuera. The Trombetas is a clearwater river draining the southeastern Guiana Shield, geologically and chemically distinct from the black waters more usually linked with Apistogramma.
The species is a rheophile, living in and beside rapids and fast channels among rocks colonised by river-weeds of the family Podostemonaceae, which cling to stone in flowing water. When the river drops in the dry season it exposes much of that rock and strands fishes in isolated pools — and it was from such pools, with rotenone, that the type series was taken during a 1985 survey of aquatic fauna in an area earmarked for a hydroelectric reservoir. That rapids setting is a long way from the planted-tank image of the genus, and it goes some way toward explaining both the fish's small size and its peculiar diet. No in-situ temperature or pH was published with the type series; the genus's broad preference for warm (roughly 75–82 °F), soft, acidic-to-neutral water is the best available proxy, but for this species it remains unmeasured.
Feeding
The most-cited fact about Apistogramma angayuara is dietary. Kullander and Ferreira examined the stomach contents of five specimens (0.5–1 in) from the rapids and found aquatic invertebrates dominant, but with an unexpected lead item: rhizopods — testate amoebae and related shelled protozoans — followed by freshwater sponges and cladocerans. That made it, in the describers' words, the first cichlid reported to take a significant proportion of rhizopods, a microphagous habit well suited to a very small fish grazing the biofilm and Podostemonaceae mats of current-swept rock.
The niche sits at a modest trophic level (FishBase models it around 3.1) and reads as a specialist's answer to life in fast water: rather than chase larger prey across open substrate like a typical eartheater, this dwarf appears to crop the micro-fauna locked into the rock-weed. It shares the rapids with a rich community — recent rapid-assessment inventories of the Trombetas rapids have catalogued dozens of fish species across many families — so its small size and microphagy may be as much about sidestepping competition as exploiting an opening.
Mating
No one has watched Apistogramma angayuara court or pair — it has never been kept, bred, or observed alive — so anything said about its mating system is comparative rather than recorded. What is certain is that both males and females in the type series had well-developed gonads, which confirms the small specimens were mature adults rather than juveniles: this really is a fully grown dwarf, not the runt of something larger.
As a genus, Apistogramma are harem- or pair-forming cave spawners. A male usually holds a larger territory overlapping the smaller territories of one or more females, with each female defending a spawning cavity while the male patrols and courts, and pertensis-group species broadly follow that pattern. It is reasonable to expect Apistogramma angayuara organises itself much the same way — scaled down, and presumably tied to the seasonal rise and fall of its rapids, when receding flow concentrates fish into pools. But the specifics, from whether it pairs or forms harems to how males display and what a courting female looks like, are genuinely unrecorded, and stating them as fact for this species would be guesswork.
Breeding
Spawning in Apistogramma angayuara has never been seen: no clutch, no fry, no parental behaviour has been documented. Apistogramma in general are cave-spawning substrate brooders — a female lays a small clutch on the roof or wall of a crevice or cavity and guards the eggs and wriggling larvae while the male defends the surrounding territory — and the pertensis group follows that template, often with modest clutches of a few dozen to perhaps a hundred eggs.
Apistogramma angayuara most likely does something similar, scaled down to its extreme small size and presumably triggered by the seasonal drop in water level that packs adults into the rocky pools where the type series was caught. But clutch size, how long the larvae are guarded, the colour of a guarding female, and the degree of male involvement are all unrecorded for this fish. Any "breeding report" in circulation would be extrapolation from its relatives, not observation — the honest statement is that the species has not been bred and its reproductive biology is unknown.
In the aquarium
Apistogramma angayuara has never been kept in an aquarium, by anyone, anywhere. Mike Wise — the most authoritative voice in the English-language Apistogramma hobby — states plainly on apistogramma.com that it has never been commercially imported and that anyone who genuinely wanted it would have to collect it themselves. The only images in circulation are photographs of alcohol-preserved holotype and paratype specimens; no live fish has ever been photographed, and as of the most recent forum records (2011) no living specimen had been maintained. Any product listing, care sheet, or breeding report claiming direct experience with this species is fabricated or misidentified.
The absence is structural. The type series came from a remote reach of the upper rio Trombetas in 1985, reachable only by river above the Cachoeira Porteira rapids and sampled in a single survey; the fish turned up in no later collecting, and a dam built in the region afterward disrupted the known locality. No subsequent field collection has been published, so even a determined hobbyist-collector would have no reliable site to target.
What follows is reasoned extrapolation from the species' biology and its closest pertensis-group relatives, not advice drawn from keeper experience.
Tank: at a maximum of about 1 in standard length (roughly an inch), this is one of the tiniest cichlids known, so a small, low-flow setup fits — a well-planted, dimly lit 10–15 US gal tank for a pair, with fine sand, smooth rounded pebbles, a scatter of dry leaf litter (Indian almond or beech), and a close-fitting cave (ceramic tube, coconut shell, or wedged flat stones) as a spawning site. Gentle filtration with minimal current matters both to mimic the stagnant-pool microhabitat the type series came from and to avoid washing away the tiny, likely fragile fry.
Water: the Trombetas is a clearwater Guiana-Shield river rather than a blackwater system, but still soft and moderately acidic; the genus broadly prefers 77–84 °F, pH 6.0–7.0, and very low hardness (under 6° dH), the best proxy available for this species.
Food: this is the one cichlid documented to feed heavily on rhizopods — testate amoebae scraped from rock and plant surfaces — alongside sponge fragments and microcrustaceans, so a captive diet would lean on live or frozen micro-invertebrates (Artemia nauplii, micro-worms, cyclops, daphnia), with suitably fine prepared foods as a supplement; anything sized for a standard Apistogramma would need scaling down dramatically for a fish under 1 in.
Tankmates: small, non-aggressive and not bottom-dwelling — tiny characins such as pencilfish or small tetras would work as dithers without competing or threatening, whereas any cichlid, loach or similarly territorial bottom fish would not. Its intraspecific aggression cannot be judged reliably, but the pertensis complex generally runs as single-pair or harem systems with one male over one or more females, so a spare tank for a subdominant fish would be prudent.
In short, the fish is not in the hobby, is almost certainly uncollectable from its known locality, and has never been bred or observed — everything above is what a careful hobbyist might try, not what anyone has.
Conservation
The IUCN Red List assesses Apistogramma angayuara as Data Deficient (assessed 7 November 2018, version 3.1, by the Instituto Chico Mendes de Conservação da Biodiversidade), with an unknown population trend. The assessment treats it as a Brazilian endemic known only from the Trombetas around the Porteira and Vira Mundo cachoeiras, describes it as rheophilic, infrequent and low in abundance, and flags the planned Cachoeira Porteira dam as the principal threat to its habitat, alongside the harvesting of aquatic resources. "Data Deficient" is the literal truth here — the species is known from one short reach, from one collecting event four decades ago, and has never been studied alive — so any firmer verdict would overreach.
The basin-wide picture is more concrete. Like most Amazon cichlids, the genus Apistogramma is broadly under-assessed rather than collapsing; the standard reference frame is Kullander's checklist contribution in Reis, Kullander & Ferraris's Check List of the Freshwater Fishes of South and Central America (2003), set against the older ecological backdrop of Lowe-McConnell's work on Neotropical fish communities. The real worry for this fish is not the ornamental trade — it is not in it — but its habitat: the 1985 type specimens were taken during a survey for a planned hydroelectric reservoir, and specialists note that later damming altered the known locality. A narrow-range rheophile tied to a single set of rapids is exactly the kind of species that impoundment, flow alteration and sedimentation can erase before it is ever properly studied. The accurate framing is blunt — formally Data Deficient, but with its one known home sitting squarely in the path of the dams and resource extraction reshaping the Guiana-Shield tributaries of the Amazon.