Taxonomy & naming
Charles Tate Regan described this fish as Acara sapayensis in 1903, in a paper on new South American fishes in the British Museum collection (Annals and Magazine of Natural History, ser. 7, vol. 12). The name rests on a single specimen — the holotype BMNH 1902.7.29.56, a fish of about 3.5 in standard length collected by W. F. H. Rosenberg at the Río Sapayo in northwestern Ecuador, an affluent of the Río Cayapas within the larger Río Santiago drainage. Eschmeyer’s Catalog of Fishes records that holotype as unique — the only specimen Regan had in hand for the name.
The species has since passed through three genera. It began as Acara, was moved to Aequidens by Eigenmann in 1910, where it sat for most of the twentieth century, and was finally transferred to Andinoacara when Musilová, Říčan and Novák (2009) erected that genus for the Pacific-slope and trans-Andean ‘blue acaras’ and their kin. Eschmeyer’s Catalog of Fishes, FishBase and GBIF now all treat Andinoacara sapayensis (Regan, 1903) as the valid name; Acara sapayensis and Aequidens sapayensis are its objective synonyms.
Where it sits inside Andinoacara has been harder to settle. The genus is informally split into an Andinoacara pulcher species group and an Andinoacara rivulatus species group, told apart partly by the predorsal scales — a single row of large median scales in the pulcher group versus gradually smaller, overlapping median scales in the rivulatus group. Earlier authors, including Stawikowski & Werner (1998) and the molecular work of Musilová et al. (2009), placed sapayensis near Andinoacara biseriatus in the rivulatus group. Then, in their 2012 revision of Andinoacara rivulatus — the paper describing Andinoacara blombergi from the neighbouring Esmeraldas basin — Wijkmark, Kullander and Barriga re-examined the holotype and found it carries the large median predorsal scales of the pulcher group; they called it ‘apparently a distinct species in tributaries of the río Santiago representing the Andinoacara pulcher species group.’ They also flagged transitional character states, and noted that the earlier DNA work attributed to sapayensis relied on an aquarium-trade specimen of uncertain identity, so the genetic placement should be treated with caution. The standing summary: a valid species whose exact affinities within Andinoacara remain unresolved on solid material.
Morphology
This is a small to medium acara. FishBase, following Kullander (2003), gives a maximum size of about 4 in total length; the few aquarium accounts that exist suggest adults of roughly 5–6 in are possible in captivity, but those figures are not anchored to verified wild specimens and are best treated as soft. The type specimens examined by Wijkmark et al. (2012) ranged from about 3–4 in standard length.
The build is typical acara — moderately deep and laterally compressed, with body depth on the order of 40 percent of standard length, a head about a third of it, a terminal mouth and a rounded caudal fin. Reported fin counts run to roughly XV (15) dorsal spines with about 10 soft rays, plus the three anal spines diagnostic of the genus followed by about 8 soft rays; meristics in the type series include 26–28 vertebrae and 24–26 scales in the E1 (lateral) row. One caution: several of these counts come from a short secondary description rather than a comprehensive modern redescription, so read them as indicative rather than definitive.
Colour is the hardest thing to pin down, because the old museum types are poorly preserved. Wijkmark et al. (2012) found that, apart from the holotype, the type specimens show very indistinct colour pattern and that the midlateral (side) blotch is absent or hard to make out — possibly a preservation artifact, since other old Andinoacara specimens also lose the blotch. The holotype itself still shows the genus’s signature dark stripes and rows of spots on the scales. Pieced together from these and from aquarium descriptions, the living fish is a beige to yellowish acara crossed by about five faint vertical bars, with a barely-there spot on the caudal peduncle, rows of dark dots along the scale rows, and the oblique, sky-blue iridescent streaks across the cheek and preoperculum that give the blue acaras their name. Sexual dimorphism has not been documented here; by analogy with its relatives, males likely grow somewhat larger with more extended dorsal and anal fin tips, but that is an inference, not an observation.
Habitat
Andinoacara sapayensis is a narrow-range endemic of the Pacific (western) slope of the Andes in northwestern Ecuador. The type locality and apparent core of its range is the Río Sapayo, a tributary of the Río Cayapas within the Río Santiago (Santiago–Cayapas) drainage in Esmeraldas Province; FishBase sums the distribution up simply as the Cayapas River drainage of northwestern Ecuador. The IUCN assessment and the Ecuadorian checklists place it in this same wet, lowland, rainforest-fed basin at low elevations, roughly 394–656 ft above sea level.
Whether it crosses into Colombia is genuinely unsettled. Wijkmark et al. (2012) noted that it ‘probably occurs in the Patía River of Colombia,’ and the ETYFish Project repeats that it also occurs in Colombia, but the supporting Colombian material — specimens from the Río Telembí and elsewhere — was treated as Andinoacara cf. sapayensis rather than confirmed. For that reason this profile maps the confirmed native range to Ecuador only and flags the Colombian occurrence as probable rather than established.
Field data on its preferred water are thin. Ecuadorian sources describe it as a fish of both clear and more turbid waters in the lowland river network, but in-situ measurements of temperature, pH and hardness at occupied sites do not appear in the accessible literature. The figures FishBase carries — about 75–79 °F, pH up to around 7.0, hardness up to about 12 °dGH — come from an aquarium atlas (Baensch & Riehl, 1985) and are best read as recommended captive conditions rather than verified habitat chemistry. The surrounding Esmeraldas/Santiago lowlands are warm, soft-water, humid-tropical rainforest streams, which is consistent with those numbers without confirming them for this species.
Feeding
No dedicated diet study exists for Andinoacara sapayensis, so its feeding ecology has to be reconstructed from brief accounts and from what is known of the genus. It is described as an omnivore that takes small insects and other animal prey in the wild, and FishBase places it at an estimated trophic level of about 3.2 — in keeping with a small, generalist, animal-leaning omnivore rather than a strict piscivore or a dedicated herbivore. Like other Andinoacara, it almost certainly forages over the substrate of its lowland streams, picking and sifting for aquatic insect larvae, small crustaceans, worms and other benthic invertebrates, and taking whatever plant and detrital matter it comes across.
In aquaria the species is reported to be unfussy, accepting prepared cichlid foods alongside live and frozen items such as bloodworm, earthworm and small crustaceans. As with its relatives, it turns more predatory with size and will take fishes small enough to swallow. None of this is specific field data, though; the wild trophic role of this particular species — its prey spectrum, its place in the Cayapas food web — simply has not been studied.
Mating
There is no published account of courtship, pair formation or territorial behaviour in wild Andinoacara sapayensis. What FishBase records — ‘males defend the territory’ during breeding — comes from a general aquarium reference rather than field observation of this species.
The reasonable expectation, drawn from the well-studied members of the Andinoacara pulcher species group to which Wijkmark et al. (2012) assigned it, is that sapayensis forms monogamous pairs that jointly hold and defend a spawning territory, with the male usually the larger and more conspicuous partner and the female taking the lead in direct egg care. Pulcher-group members are also noted for laying their eggs on movable substrates, unlike some relatives that use fixed surfaces. Whether sapayensis follows that pattern specifically has not been confirmed. In short, its mating system is presumed to resemble that of the blue acaras, but the species’ actual reproductive behaviour in the wild remains undocumented.
Breeding
Breeding in Andinoacara sapayensis has not been documented in the wild, and verified captive spawning reports are essentially absent — the fish is so rare in the hobby that almost everything once kept under the name was a misidentified relative. The one quantitative figure in circulation, ‘about 400 eggs,’ reaches FishBase from an aquarium atlas (Baensch & Riehl, 1985) and should be read as a rough, atlas-level estimate rather than a measured clutch for this species.
Every member of the Andinoacara pulcher and Andinoacara rivulatus species groups in which breeding has been observed is an open, biparental substrate brooder: they lay adhesive eggs on a cleaned surface, both parents guard and fan the clutch, and the pair shepherds the free-swimming fry afterward rather than mouthbrooding them. Andinoacara sapayensis is overwhelmingly likely to follow that template — a substrate-spawning, biparental cichlid with extended parental care — but clutch size, egg and larval development, spawning triggers and fry-guarding behaviour have not been described for the species itself. It is one of the clearest gaps in its biology.
In the aquarium
In practice, Andinoacara sapayensis is almost never kept as a confirmed fish — it has been a name more than a living animal in the hobby. The handful of individuals sold under it through the 1980s and into the 1990s have since been recognised as misidentified relatives, and the published record appears to hold just one verified aquarium photograph of a confirmed specimen, taken by Zuzana Musilová, co-author of the 2009 genus revision. Treat any fish offered under this name with suspicion. The guidance below is therefore extrapolated from close relatives — above all the well-documented Andinoacara pulcher (blue acara), to which Wijkmark, Kullander and Barriga (2012) assigned sapayensis on morphological grounds.
Tank: from the type-series measurements and the andinoacara.com profile, adults reach roughly 5–6 in standard length — well short of the true green terror (Andinoacara rivulatus, 8.5–12 in) and closer to the blue acara. A base footprint of about 47 in × 17.5 in (48 × 18 in, roughly 55 US gal net) suits a single fish or a bonded pair; go larger if you can, since the fish digs and defends territory around spawning. Give it a fine sand or small-gravel bed for excavating, a few smooth rounded rocks or flat stone slabs (which double as spawning sites), driftwood to break up sightlines, and dim light with floating cover. Rhizome-anchored plants such as Anubias and Java fern outlast rooted aquatics, and a conventionally planted tank is unrealistic for a digging omnivore.
Water: this is the one area with real data behind it. The home basin — the Santiago–Cayapas watershed of Esmeraldas Province — is a warm, humid lowland system; in-situ surveys (Rebolledo Monsalve et al. 2022) measured roughly 77–81 °F and pH spanning about 5.6–8.3 across sites, with unimpacted control stations near neutral. The FishBase aquarium figures (75–79 °F, pH up to ~7.0, hardness up to ~12 °dGH) sit comfortably inside that and make a sensible target: soft to moderately hard, near-neutral to slightly acidic water, tropically warm. The fish is unlikely to be fussy within that range, but should not be held in chronically hard, alkaline conditions.
Tankmates: judging by the pulcher group, its temperament is cichlid-standard rather than green-terror dramatic. Where Andinoacara rivulatus is aggressive enough that Seriously Fish recommends keeping it alone or as a mated pair in 59 in tanks, pulcher-group acaras are relatively peaceful for medium cichlids and will share space with fish too large to swallow. Reasonable companions include other medium-sized New World cichlids of comparable temperament, larger characins (silver dollars, bleeding-heart tetras) and hardy catfish (Corydoras, Ancistrus, mid-sized loricariids). Small tetras, livebearers and anything small enough to fit in the cichlid’s mouth are not viable, especially once a pair is in breeding condition — during active spawning the pair defends its territory vigorously, and even robust tankmates may need to be removed.
Common mistakes: the biggest is the trade-name muddle. ‘Green terror’ has been hung on at least three Andinoacara — Andinoacara rivulatus (the original bearer of the name, from Peru and coastal Ecuador), Andinoacara stalsbergi (a similar, large, aggressive Peruvian species often sold interchangeably with rivulatus), and, historically, misidentified sapayensis. The two genuine green terrors reach more than twice the size of sapayensis and want larger tanks, harder water and more aggressive tankmates, so a mislabelled fish ends up badly matched to its setup. Anyone buying a fish labelled Andinoacara sapayensis today should check it against published photographs of both Andinoacara rivulatus and Andinoacara stalsbergi before trusting the label.
Conservation
The IUCN Red List assesses Andinoacara sapayensis as Data Deficient (assessment e.T64791043A66363672, by Pablo Arguello and Pedro Jiménez-Prado of the Escuela Politécnica Nacional and the Universidad Católica de Esmeraldas; assessed 6 October 2014, published 2016). The category captures exactly the situation this profile describes: a species known from very few specimens, with little information on its population size, range limits or ecology, leaving assessors unable to judge its conservation status. It carries no CITES or CMS listing, and FishBase rates its fishing vulnerability as low. It is of no commercial fisheries interest, though it is locally consumed and turns up occasionally in the ornamental trade.
The broader picture for its home waters is more worrying. The Esmeraldas and Santiago–Cayapas lowlands of northwestern Ecuador hold a distinctive, range-restricted freshwater fish fauna under mounting pressure from deforestation, the spread of oil-palm and other croplands, urbanization, and — above all — pollution from gold mining, the same threats that have pushed several co-occurring western-Ecuadorian endemics into threatened categories. A small fish confined to one or two river systems in this region is, by definition, exposed to local habitat degradation, even if the data needed to quantify that risk for sapayensis specifically do not yet exist. The most useful thing that could happen for this species would simply be for someone to go and study it.