Taxonomy & naming
Cichlasoma araguaiense was described by the Swedish ichthyologist Sven O. Kullander in 1983, in his landmark 296-page monograph A Revision of the South American Cichlid Genus Cichlasoma (Naturhistoriska Riksmuseet, Stockholm). That revision was a watershed: Kullander restricted Cichlasoma — a name that had ballooned to hold well over a hundred Central and South American cichlids — to a tight assemblage of about a dozen small, generalized, three-to-six-anal-spined South American 'port cichlids' centred on the type species Cichlasoma bimaculatum (Linnaeus, 1758). The fallout for hobbyists and systematists alike was drastic, since it freed the name Cichlasoma from the host of Central American fishes that had long carried it. Cichlasoma araguaiense was one of several new species Kullander erected in that work, alongside Cichlasoma amazonarum, Cichlasoma orinocense, Cichlasoma orientale, Cichlasoma sanctifranciscense, Cichlasoma paranaense, Cichlasoma boliviense and Cichlasoma pusillum. The holotype (BMNH 1980.1.9.1, in the Natural History Museum, London) and its paratypes came from a small igarapé (forest creek) tributary to the Igarapé Sangadina, itself a tributary of the Rio das Mortes in the Araguaia drainage, one kilometre from Xavantina in Mato Grosso, Brazil. The species had effectively been 'seen' long before it was named — Castelnau reported a specimen as Chromys punctata? in 1855, and Haseman's 1907–1910 Carnegie Museum expedition catalogue listed a 3.5 in fish from the Rio do Sono (a Tocantins tributary) under the blanket name Cichlasoma bimaculatum, material Kullander later reassigned to araguaiense. The species remains valid (confirmed by Kullander in Reis et al. 2003 and by Ottoni 2011), and within the cichlasomatine radiation it sits among the small, plesiomorphic acaras near the base of the Neotropical cichlid tree.
Morphology
Cichlasoma araguaiense is a small, moderately deep-bodied acara of conventional 'port-cichlid' build — laterally compressed, with a gently sloping forehead, a terminal mouth and the four (occasionally more) anal-fin spines that characterise the genus. It is modestly sized: Kullander's original type material reached only about 3.5 in standard length, and his 2003 checklist treatment carried that figure, but a later length-weight study indexed by FishBase records considerably larger fish — to 6 in SL in males and 5 in SL in females, with a maximum published weight near 152 g. The species is thus best described as a roughly 3.5–6 in fish, with the smaller figures reflecting wild-caught reference specimens and the larger ones well-fed or older individuals. In life it is a warm brassy-tan to olive fish, the flanks often shot through with iridescent blue-green flecking and a pattern of dark blotches and a mid-lateral spot in the manner of its close relatives — markings that fade and shift with mood and that for more than a century made these fish maddeningly hard to tell apart without locality data (Haseman remarked in 1911 that he could not reliably separate them except by anal-spine count). Sexual dimorphism follows the genus pattern: males grow larger and somewhat more robust, while ripe females are deeper- and fuller-bodied. As with all Cichlasoma s.s., precise field identification leans heavily on meristics and provenance rather than colour alone.
Habitat
The species is endemic to central Brazil, where it occupies the Tocantins and upper Xingu river basins of the eastern Amazon system — the type series, despite the epithet, comes from an Araguaia-drainage creek (the Rio das Mortes feeds the Araguaia, which in turn joins the Tocantins). FishBase and the Catalog of Fishes both give the range as the Amazon River basin in the Tocantins and upper Xingu drainages, Brazil; it has not been recorded outside the country. The original specimens were taken from a small igarapé — a shaded forest creek — and the species' relatives are typically fishes of quieter, marginal waters: streams, creeks, lagoons and the vegetated edges of larger rivers rather than open main-channel current. FishBase characterises it as a freshwater, benthopelagic fish of the tropics, with reported water of pH 7.0 and upward, hardness to roughly 20 dH, and a temperature band of about 73–81 °F. As a clear- to slightly stained-water cichlid of the Brazilian Shield drainages it is found in shallow, accessible habitat; field collection of the type and reference material was made in shallow creek water on the order of 0–2 metres deep, the band in which these small acaras are typically netted. In-situ chemistry for this particular species is sparsely documented, and the figures above are best read as the species' tolerated/typical envelope rather than a dense set of field measurements.
Feeding
No dedicated diet study of Cichlasoma araguaiense has been published, but its trophic role can be read confidently from its anatomy and from its well-studied congeners. FishBase places it at a trophic level near 3.0 — squarely in the generalist range — and the genus as a whole comprises opportunistic benthic omnivores. The closely related black acara, Cichlasoma bimaculatum, has been documented (in its native range and as an invader in Florida) as a generalist omnivore taking small crustaceans, insect larvae, other invertebrates, small fishes and plant and detrital material, a flexible diet that travels well with the body plan. Cichlasoma araguaiense almost certainly works the same niche: a small-mouthed forager picking invertebrates, larvae and organic matter from the substrate, leaf litter and submerged structure of its forest creeks and river margins, and taking some plant and detrital material besides. This dietary plasticity — the same trait that has made bimaculatum a successful colonist far from home — is typical of the genus and underlies its 'high resilience' rating in fisheries models.
Mating
Cichlasoma araguaiense has not been the subject of a published ethological study, but the genus is uniformly biparental, and the reproductive behaviour of its relatives is well characterised. These are monogamous, pair-bonding cichlids in which a male and female form a lasting bond, jointly stake out and defend a territory, and clean a spawning surface together before laying. The classic laboratory work of G. P. Baerends on the pre-spawning behaviour of a port-cichlid (published 1984, under the older name Aequidens portalegrensis) became a foundational study of cichlid courtship sequences, and it is from this lineage of small acaras that much of our textbook understanding of cichlid pair behaviour derives. In Cichlasoma proper, courtship runs through the familiar repertoire of lateral displays, fin-spreading, jaw-locking and substrate-cleaning, with both partners sharing territorial defence. Outside of breeding these are comparatively unobtrusive, modestly territorial fish; the intensity ramps up sharply once a pair commits to a site and begins guarding.
Breeding
Like all members of the genus, Cichlasoma araguaiense is a biparental open- or substrate-spawner rather than a cave specialist or mouthbrooder. The pair selects and cleans a firm surface — a flat stone, a root, a leaf or a patch of cleared substrate — and the female lays an adhesive sheet of eggs that both parents then guard and fan, with the female typically tending the clutch most closely while the male patrols the territory perimeter. After hatching, the wrigglers are moved to pits and the free-swimming fry are shepherded and defended by both parents as a tight school, in the substrate-brooding pattern shared across the small acaras. A published photograph by Uwe Werner shows Cichlasoma araguaiense tending a brood of fry, confirming that the species follows this template in practice. No species-specific clutch count has been published; congeners in this size class are genus-typical moderate-fecundity spawners, laying on the order of a few hundred eggs per clutch (the related black acara is reported producing several hundred to roughly a thousand). FishBase rates the species as highly resilient, with a minimum population-doubling time under 15 months, consistent with the productive, parentally-attentive breeding strategy that lets these acaras recover quickly and, in the case of bimaculatum, colonise new waters.
In the aquarium
Cichlasoma araguaiense is a rarely-kept fish — it has no settled common name and almost never appears in the trade, so there is little dedicated hobbyist literature on it specifically. What guidance exists comes by analogy with its better-known relatives, the 'port cichlids' (Cichlasoma portalegrense, Cichlasoma dimerus, Cichlasoma bimaculatum and kin), which have a long and forgiving aquarium history. As a roughly 4.5–6 in biparental acara, it would want a tank of around 47 in / 200+ litres for a pair, more if kept in a community, with a soft sand bottom, driftwood and roots, some flat stones or broad leaves as potential spawning sites, and planted or shaded margins to break up sightlines. Water should track its native envelope: temperature about 73–81 °F, pH from neutral upward (around 7.0 and above is reported), and soft-to-moderately-hard water (FishBase notes hardness up to ~20 dH), with the usual regimen of regular partial water changes and effective filtration kept at moderate flow — these are fish of quiet creeks, not torrents. Feeding is undemanding given the genus's omnivorous flexibility: a varied diet of quality sinking pellet or flake supplemented with live or frozen invertebrates (bloodworm, brine shrimp, daphnia, small earthworms) and occasional plant matter suits it well. Temperament is that of a typical small acara — generally peaceful outside of breeding, but a bonded pair will hold and defend a territory and can become pugnacious toward tankmates and toward each other once spawning begins, so a tank with cover and escape routes is prudent. It is best regarded as a fish for the cichlid specialist or biotope enthusiast rather than the general community keeper, valued for what it is — an authentic, little-seen piece of the genus Cichlasoma — rather than for colour or novelty.
Conservation
The IUCN Red List assesses Cichlasoma araguaiense as Least Concern (assessed 7 November 2018 by the Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio), published 2022), with a population trend recorded as stable. The species carries no CITES listing and is rated harmless to humans and of low fishing vulnerability. As a small, widely-distributed habitat generalist spread across the Tocantins and upper Xingu drainages, it is far less exposed than the basin's many narrow-range endemics, and there is no evidence of a species-level threat. That said, its home waters sit in one of the most heavily impacted regions of Amazonia: the Tocantins–Araguaia and Xingu systems are dammed (the Tucuruí and Belo Monte hydroelectric complexes among them) and are under pressure from deforestation, agricultural expansion across the Cerrado headwaters, and altered flow and sediment regimes. None of these is documented as a present danger to this particular cichlid, but they are the backdrop against which the long-term status of its shield-drainage habitat should be read.