Taxonomy & naming
Uwe Römer and Ingo Hahn described Apistogramma aguarico in 2013, in a paper devoted entirely to the new species in the journal Vertebrate Zoology (volume 63, part 2, pages 171–181). The description rests on nine specimens, all collected in the 1980s and long held at the Field Museum of Natural History in Chicago, where Römer examined them. The holotype is catalogued as FMNH 101588; the paratypes are split between the Field Museum (FMNH 117725 and 117726) and the Senckenberg collection in Dresden (MTD F 32379). Both the Catalog of Fishes and FishBase list the name as valid in its original combination, Apistogramma aguarico Römer & Hahn, 2013, and the genus sits in the Neotropical cichlid subfamily usually treated as Geophaginae (Cichlinae in the Catalog of Fishes).
The authors place Apistogramma aguarico in the Apistogramma eunotus complex of the wider Apistogramma regani lineage — one of the 'cruzi-like' dwarf cichlids in hobby shorthand. The description helped sort out a long-running muddle among the small, plain Apistogramma of the upper Napo. In the same waters, Römer and colleagues had described Apistogramma playayacu, and the field naturalist Mike Wise and collector Tom Christensen, who had collected in the Aguarico drainage, debated openly on apistogramma.com whether fish reaching aquarists as Apistogramma playayacu might in fact be Apistogramma aguarico, or yet another undescribed 'cruzi-like' form — they counted at least three such forms in the upper Napo. That uncertainty is part of the story: Apistogramma aguarico was carved out of a knot of look-alikes whose boundaries are still being worked out from preserved museum material rather than living populations.
The species name 'aguarico' is a place name used as a noun in apposition, for the type locality in the Río Aguarico system; it is not a Latinized adjective and does not change with gender.
Morphology
Apistogramma aguarico is small: FishBase records a maximum of about 2 in standard length for the examined material (male or unsexed), in line with the modest size of the type series. The body is the fusiform, laterally compressed shape typical of the genus. Meristics from the original description are a dorsal fin of 15–16 spines and 6–7 soft rays, and an anal fin of 3–4 spines and 5–6 soft rays.
Römer and Hahn diagnose the species by a set of features seen in adult males. The caudal fin is basically truncate, transparent and unmarked, and in the largest individuals both lobes carry filamentous, streamer-like extensions — a useful field mark, but one restricted to the biggest fish; the authors note that only the two largest of five males in the collection showed it, and the chosen holotype lacks an intact extended tail. The first membranes of the dorsal fin are pointed and drawn out to nearly double the length of their spines, giving the fin a serrated outline. The pectoral-fin base is whitish to ivory and free of dark markings, standing out against the otherwise yellowish-brown body. A broad lateral band runs along the upper scale rows and ends on the upper third of the caudal peduncle, separated from a rectangular spot on the centre of the caudal base whose pale-brown centre can make it look divided. Two to three fragmentary rows of oval abdominal spots run along the flank, strongest toward the rear above the anal fin — the original abstract describes up to four irregular abdominal lines built from highly variable spots. The gill cover is markedly darker than the body below the lateral band, and the head carries distinct preorbital, postorbital and cheek stripes. There are no black markings under the head or body apart from a short, narrow grey pre-anal stripe that shows only in very large specimens. As in the genus generally, males grow larger and more finely finned than females; the description is male-based, and little is documented of female coloration in life.
Habitat
Apistogramma aguarico is known with certainty only from its type locality: a lagoon — an oxbow, or 'cocha' — connected to the Río Lagartococha, an affluent of the Río Aguarico within the larger Río Napo system, in the northeast of Ecuador near the Peruvian border (Sucumbíos region, in the Cuyabeno–Lagartococha wetland complex). The original description places the lagoon about 16 mi upstream from the Lagartococha's confluence with the Aguarico. FishBase summarizes the distribution simply as the Río Napo system in Ecuador.
The published coordinates carry a clear error worth flagging. Both the original description and the Catalog of Fishes give the locality as roughly 9°47′S, 75°57′W — but that point lies hundreds of kilometres away in central Peru, not in northeastern Ecuador, and is plainly a transcription slip, most likely for a latitude near 0°47′S. The Lagartococha system actually sits close to the equator, at about 0°30′–0°40′S and 75°15′W; an independent museum collection from the Lagartococha/Aguas Negras of the Aguarico drainage is georeferenced at 00°31′38″S, 075°15′41″W. The point mapped for this species on the Atlas is therefore a corrected estimate, placing the type lagoon on the Lagartococha roughly 16 mi above the Aguarico confluence, rather than the literal, erroneous figure from the paper.
The biotope is a quiet, lowland Amazonian backwater rather than open river — the kind of warm, slow, often tannin-stained 'cocha' that dwarf cichlids favour, with leaf litter and submerged wood. No in-situ water chemistry was published with the description, so the exact values are unknown for this species. The chemistry shown on this page — warm water around 75–82 °F and soft, acidic conditions near pH 5.0–6.5 — is basin-typical for upper-Napo blackwater 'cochas' rather than a set of measurements from this lagoon, and should be read as a guide to the habitat type, not a record of it.
Feeding
Nothing has been published on the diet or feeding behaviour of Apistogramma aguarico in the wild; the species is known only from preserved specimens, with no stomach-content or field-foraging study. By the well-established habits of the genus, it can be inferred to be a micropredator of the leaf litter and substrate, picking small benthic invertebrates — insect larvae, microcrustaceans and other meiofauna — from sediment and detritus, often by taking in mouthfuls of substrate and sorting out the edible particles. FishBase places it at an estimated trophic level of about 3.3, but that figure is modelled from its size and relatives rather than measured. Any more specific account of what this fish eats would be invention.
Mating
The mating system of Apistogramma aguarico has not been documented — there is no published account of courtship, pair formation or spawning, in the wild or in aquaria. The genus Apistogramma is broadly polygynous or harem-forming, a larger male defending a territory that overlaps the smaller territories of several females, each guarding a cave; some species pair off instead. Which pattern Apistogramma aguarico follows is unknown. The describers and the hobbyists who collected related 'cruzi-like' fish in the Aguarico note that even the largest males develop the streamer-tipped tail only late, which hints that — as in many dwarf cichlids — size and fin development feed into male competition and female choice. That, though, is inference from close relatives, not observation of this species.
Breeding
Breeding has not been documented for Apistogramma aguarico, in the wild or in captivity. No clutch size, spawning behaviour, egg description or account of fry development has been published. Members of the genus are overwhelmingly cave-spawning substrate brooders with female-led parental care: the female lays a small clutch on the roof of a sheltered cavity — a crevice, a hollow under wood, or a snail shell or leaf in aquaria — then tends and fans the eggs and leads the free-swimming fry while the male guards the wider territory. Apistogramma aguarico is presumed to follow the same pattern, but that is an expectation drawn from its relatives rather than a recorded fact. Whether it has ever been bred by aquarists under its own name is unclear, tangled up with the long-standing confusion with Apistogramma playayacu and other look-alikes from the upper Napo.
In the aquarium
Apistogramma aguarico is, honestly, almost unknown as an aquarium fish under its own name. It was described in 2013 from museum material, and the handful of European hobbyists who have kept what they believe to be Apistogramma aguarico — chiefly fish that came through the collector Albertini from Ecuador around the time of the description — could not confirm the identification. As the discussion on apistogramma.com between Mike Wise and Tom Christoffersen makes clear, the line between Apistogramma aguarico and the other 'cruzi-like' Apistogramma of the upper Napo — including Apistogramma playayacu and at least one further undescribed form — has never been resolved to the satisfaction of specialists working with live fish. If you have acquired a fish labelled Apistogramma aguarico or Apistogramma cf. aguarico, treat that label as provisional.
With that caveat, the husbandry can be drawn from two sources: the biotope (a warm, still, tannin-stained oxbow) and the closely related Apistogramma eunotus, the best-documented member of the complex.
Tank: at least 60 × 12 in base (roughly 15 US gal) is the practical minimum for a pair. A trio of one male and two females — consistent with the harem system expected for the genus — wants a footprint of 80 × 15.5 in or more, so each female can hold a distinct territory. Males of small 'cruzi-like' Apistogramma can be rough on females, and extra females spread that pressure.
Cover: the biotope calls directly — fine sand or smooth gravel, a layer of dried leaf litter (catappa, beech or oak all work), and driftwood or bogwood arranged into shaded recesses, plus at least one small cave per female. Coconut shells, terracotta pots, or snail-shell clusters laid on their sides all serve; size the caves so the male cannot follow the female inside (Seriously Fish, Apistogramma eunotus profile). Low-light plants (Cryptocoryne, Anubias, Microsorum) and a patch of floating cover to soften the light complete the picture. Keep flow gentle — a sponge filter or low-flow hang-on-back beats a powerhead, since this is a still-water fish.
Water: chemistry is the single most critical variable. Basin-typical upper-Napo blackwater puts pH in the 5.0–6.5 range, temperature at 75–82 °F, and hardness very soft — aim for conductivity below 100 µS/cm (roughly 0–4 °dH). Many 'cruzi-like' Apistogramma will tolerate slightly wider parameters day to day, but spawning and, above all, egg hatching in this part of the genus are tied to low pH and near-zero hardness; Mike Wise has noted on apistogramma.com that blackwater species from the upper Rio Negro and similarly soft systems often need pH below 5.5 for eggs to develop. Soft, acid water is not optional for reproductive success here. Reverse-osmosis water buffered with a little peat extract or catappa leaf is the reliable route; untreated tap water in most cities will not do. Small, frequent changes (10–15% weekly) suit a lightly stocked tank better than large, infrequent ones.
Food: no difficulty. Like all Apistogramma, this is a benthos picker that readily takes small live or frozen invertebrates — Artemia nauplii, Daphnia, bloodworm (Chironomus larvae) and Cyclops. Acclimated fish accept dry microgranules, but live and frozen items should anchor the diet, both for nutrition and to bring fish into spawning condition.
Tankmates: the safest choices are small, non-competitive, blackwater-adapted species that use different water levels — pencilfish (Nannostomus), small tetras from similar Napo or Amazon tributaries, or otocinclus. Avoid robust or fin-nipping species, and do not house multiple Apistogramma males without substantial visual breaks. Keep wild-caught fish to their own group and a few dither fish until settled.
Common mistakes: the recurring failure with these fish is trying to spawn them in water that is too hard or too neutral. The second is too little cover — both sexes are shy, and a sparse tank produces stressed, unhealthy fish. The difficulty level, to the extent Apistogramma aguarico is kept at all, is intermediate-to-advanced — not because the fish is fragile, but because consistently maintaining very soft, acidic water and sourcing correctly identified stock are genuine hurdles. Given the rarity of confirmed material and the ongoing identification uncertainty in the upper Napo, successful breeding under the correct name has not been documented in the published or hobbyist literature.
Conservation
Apistogramma aguarico has not been assessed by the IUCN Red List — its global status is Not Evaluated, confirmed both by the absence of any record in a direct Red List search and by FishBase, which lists IUCN, CITES and CMS status all as Not Evaluated. It carries no trade or conservation listing.
That absence of a formal assessment leaves a species that is, on the evidence, naturally narrow-ranged and very poorly known: confirmed only from a single lagoon in the Cuyabeno–Lagartococha wetlands of northeastern Ecuador, and — as far as the published record shows — never re-collected and documented as such since the original 1980s material. The surrounding region faces the familiar pressures on the western Amazon lowlands: oil extraction and its pollution in the Aguarico/Sucumbíos area, deforestation, and the broad threats to seasonally flooded wetland connectivity in the Napo basin, though none has been studied in relation to this particular fish. Much of the Lagartococha system lies within the Cuyabeno Wildlife Reserve and a Ramsar-listed wetland complex, which gives the habitat some indirect protection. The honest summary is that Apistogramma aguarico is data-deficient in the everyday sense, even without the formal label: its range, abundance and ecology are essentially undescribed beyond the type collection.