Taxonomy & naming
Sven O. Kullander, the Swedish ichthyologist, named Apistogramma payaminonis in his 1986 monograph Cichlid Fishes of the Amazon River Drainage of Peru — a Peru-titled work that, confusingly, described this particular species from Ecuadorian material. Eschmeyer's Catalog of Fishes fixes the holotype as FMNH 96564 (Field Museum of Natural History, Chicago); the type locality is a headwater tributary of the Río Tutapishcu above Ahuanopaccha, in the Río Payamino drainage of Napo Province, Ecuador, at 00°31.12'S, 77°20.42'W. The paratype series — MCZ 40327, fifteen specimens — is recorded as missing. The genus itself was erected by C. Tate Regan in 1913 as a replacement name, and FishBase, GBIF, and the IUCN Red List all corroborate the genus, family, and Data Deficient status.
Apistogramma payaminonis sits in the Apistogramma nijsseni complex, a cluster of close, strongly sex-coloured upper-Amazon dwarfs that also holds Apistogramma nijsseni, Apistogramma panduro, and Apistogramma baenschi. In 2015 Uwe Römer and colleagues redescribed it in Vertebrate Zoology, working from the only two surviving type specimens; in the same paper they split off two long-confused Peruvian look-alikes, Apistogramma wolli and Apistogramma feconat, that had drifted through the literature and hobby under or near the payaminonis name. That redescription remains the single most important modern source on the fish. The Catalog of Fishes maps a wider range across the upper Amazon of Colombia, Ecuador, and Peru, but precision matters here: specimens unambiguously identifiable as Apistogramma payaminonis are known only from the Río Payamino system in Ecuador, and the Colombian record rests on a tentative match — a form the keeper-naturalist Tom Christoffersen labelled Apistogramma sp. 'D3' from Caquetá — that the describers themselves flag as unconfirmed.
Morphology
This is a true dwarf. Römer et al. (2015) give males up to about 1.5 in standard length and females to roughly 1 in, and FishBase rounds the maximum to 1.5 in SL — a fish measured in fractions of an inch. The body is moderately elongate and laterally compressed, moderately high-backed, with a fairly large head: the standard nijsseni-complex build.
Colour is where the sexes part company. Apistogramma payaminonis is strongly dichromatic, and the redescribers note that males are polychromatic on top of that — some are yellowish to light green overall, others a paler blue with a yellowish head. Both sexes carry dark lateral spots over the third and fourth vertical bars and a black mark at the pectoral-fin base, both stronger in females, plus a caudal spot at the tail base that is rounder in females and more squarish in males. Females usually show two clear lateral spots, most vividly in breeding mood; males usually show just one. The caudal fin and dorsal-fin lappets are milky white to faintly yellowish and largely unmarked. Because live colour went essentially undocumented for decades, much of what the hobby once pictured as 'payaminonis' has since been reassigned to Apistogramma wolli or other complex members — reason enough to be wary of any photograph offered under the name.
Habitat
Apistogramma payaminonis is a headwater fish of the upper Amazon, tied to the Río Payamino, a clearwater tributary of the Río Napo on the Andean piedmont of Amazonian Ecuador. Verifiable records come only from the type locality and a second, nearby site in the same Payamino system, at an elevation the IUCN puts between about 200 and 1312 ft. This is a small-stream specialist, not a fish of the great river channels — and a December 2024 AMAZONAS Magazine field account of collecting in the Río Payamino describes the kind of water it lives in: a river hard to seine, broken into rocky and gravelly stretches with narrow sandbanks tucked behind the bends.
The only detailed ecology on record comes with the type series (noted by D. Stewart in Kullander 1986 and quoted again by Römer et al. 2015): a slow backwater off a swift forest stream 26–33 ft wide, its clear water slightly acidic at about pH 6.4 and a relatively cool 73 °F, just 2–3 ft deep with visibility over half a metre, the bank undisturbed rainforest and the bed a mix of bedrock, large rocks, dead wood, and silty sand. The redescribers state plainly that no reliable new ecological information has been added since 1986. The frame that matters, then, is the soft, cool, slightly acidic clearwater of the Napo system's Andean-foreland forest streams — fed by primary-forest runoff and structured by submerged wood, rock, and leaf litter.
Feeding
No dedicated diet study exists for Apistogramma payaminonis — better stated plainly than papered over — so its feeding ecology is read from its body plan, its leaf-litter habitat, and the well-documented habits of its nijsseni-complex kin. FishBase puts it at a trophic level near 3.3, a small, invertebrate-leaning micropredator, while the IUCN simply calls it an omnivorous benthopelagic species of pristine waters. In practice, dwarf cichlids of this kind work the leaf litter and the benthic zone, taking in mouthfuls of fine sand and detritus and sorting out aquatic insect larvae, microcrustaceans, and other small invertebrates, mostly in the lower third of the water column.
Within its community it is a small, cryptic fish threading through submerged wood and leaves, where the cover serves at once as its foraging ground and its refuge from larger predators — a typical Apistogramma of the forest-stream floor rather than a feeding specialist.
Mating
Direct courtship observations of Apistogramma payaminonis are essentially absent, so its mating system is inferred from its close, aquarium-documented relatives in the nijsseni complex. These are harem-polygynous dwarfs: a dominant male holds a comparatively large territory that overlaps the smaller territories of several females, each defending a patch built around a potential spawning cave. When a female ripens she courts within her own territory and picks a cavity whose mouth is small enough to shut out the much larger male. Pair bonds are loose and female-centred, and around spawning the female becomes fiercely territorial — in the tight quarters of a tank she can turn lethally aggressive toward a male that lingers too close, as keepers of Apistogramma nijsseni and its kin report again and again. Expect the standard complex picture, in other words: real territoriality, female-led cave defence, and a temper out of all proportion to the fish's tiny body.
Breeding
Apistogramma payaminonis has barely been bred in captivity, so its reproductive biology is extrapolated from the nijsseni complex rather than watched in detail. These are cave-spawning substrate breeders with strongly female-biased care, and FishBase records the pattern directly for this species: the eggs are attached to the ceiling of a cave and tended by the female through the egg and larval stages. In well-studied complex members she does nearly all of the work — guarding, fanning, and shepherding the free-swimming fry — while the male, if he is tolerated at all, patrols the wider territory. Clutches in related nijsseni-group dwarfs are modest, from several dozen to a couple of hundred eggs, hatching in roughly two to three days and giving free-swimming fry about a week after spawning, the exact timing set by temperature. Genus-wide, Apistogramma also show temperature-linked sex determination in the fry, so soft, slightly warm, acidic water shapes not just the hatch rate but the sex ratio of the brood. For this species specifically, the honest line is that the wild nest has never been described and verified captive spawnings are episodic at best; what holds is the cave-spawning, female-guarded mode it shares with the rest of the complex.
In the aquarium
Few importers have ever offered Apistogramma payaminonis; it is one of the rarest dwarves in the hobby — not in the CITES sense, just genuinely scarce in the trade — and because the name was misapplied for years to Apistogramma wolli and related complex fish, even the keeper logs that exist are hard to trust. Treat it as a project fish; where species-specific data run out, the notes below are complex-typical.
Water: soft to very soft and slightly acidic — pH 6.0–6.5, in the low-to-mid 72–81 °F band. The field reading was 73 °F and pH 6.4, cool and gentle rather than the warm blackwater extreme sometimes used for Amazonian dwarfs; keep hardness low and cut hard tap water with reverse-osmosis water before conditioning. A settled pH of 6.5 beats an acid extreme you can't hold — stability matters more than the number.
Tank: 15–20 US gal suits one male with one or two females; tiny as they are, guarding nijsseni-complex females have killed or badly harassed males in far larger tanks, so don't crowd them. Floor it with fine sand — not gravel, which blocks their natural sifting — scatter dried oak or Indian almond leaves, and add bogwood, roots, and small flat stones for cover and cave mouths. Dim the light with floating plants or water lettuce, and give each female two or three small caves or coconut-shell halves, set out of one another's constant line of sight.
Tankmates: small, peaceful, mid-to-upper swimmers that won't raid the bottom — soft-water South American tetras such as ember or neon tetras, with Corydoras or small Otocinclus on the floor if the tank is roomy enough that territories don't collide. Avoid anything big enough to eat a dwarf cichlid, anything that digs hard, and anything that competes for caves; keep it as a display centrepiece, not one voice in a busy, assertive community.
Sexing and conditioning: sexing is easy — males are the larger, more colourful sex (see Morphology), and a female in vivid yellow-black dress is signalling a spawn is near. Condition a pair on varied live and frozen foods — daphnia, artemia nauplii, bloodworm, small cyclops — plus a good micro-pellet. One genus caveat: temperature may skew Apistogramma fry sex ratios (cooler toward females, warmer toward males), so specialists often hold the tank in the lower part of the range around spawning, unconfirmed as that is here. Overall it rates moderate for an experienced dwarf-cichlid keeper and harder for a newcomer — chiefly because it is so seldom available that there is no hobby literature to lean on, and because misidentified stock is a real risk.
Conservation
The IUCN Red List assesses Apistogramma payaminonis as Data Deficient — assessed on 9 October 2014 by P. Arguello and P. Jimenez-Prado and published in 2016 — meaning there is simply too little on its range, population, and trends to assign a threat category; the assessors add that more fieldwork could well move it to Least Concern. It carries no CITES listing and, per the IUCN, is not known to be used or traded, unsurprising for a fish that never took hold in the hobby even as its showier relatives are routinely exported.
The real concern is range and habitat. With such a restricted known distribution in the western Amazon, the redescribers argue Apistogramma payaminonis should be treated as potentially endangered — any local disturbance carries outsized risk for a narrow-range, low-density fish. The IUCN names a single threat, pollution from oil extraction, and Römer et al. (2015) develop it for the wider western Marañón–Napo region: repeated oil spills and heavy-metal and hydrocarbon contamination beyond legal limits in parts of the Río Tigre and Río Corrientes drainages, alongside gold mining and forest clearance, with Apistogramma laboratory-confirmed to be highly sensitive to such contaminants. The honest summary is that this is a least-known species rather than a confirmed-imperilled one — formally Data Deficient — but one living in a strained basin where industrial pollution and deforestation, not the aquarium trade, are the pressures that matter.