Taxonomy & naming
Cichlasoma amazonarum was described by the Swedish ichthyologist Sven O. Kullander in 1983, in his monographic revision of the South American cichlid genus Cichlasoma, published by the Swedish Museum of Natural History. The type locality is a small right-bank tributary of the Río Ampiyacu — the Sacarita del Tuyé, a little upstream of Pebas in Loreto, Peru — and the holotype (NRM 39271) is held in Stockholm, supported by a large paratype series scattered across museums in Europe and the Americas. The name is an original combination and has never been reassigned; the Catalog of Fishes lists it as valid as Cichlasoma amazonarum Kullander 1983, in subfamily Cichlinae, tribe Cichlasomatini. Before Kullander's work the fish had no name of its own: specimens now called amazonarum were lumped under the catch-all Cichlasoma bimaculatum, and at least one earlier worker (Lüling) misidentified Peruvian material from Yarina Cocha as Cichlasoma facetum or as an Aequidens. Kullander's revision is what reduced the genus Cichlasoma from a sprawling assemblage of hundreds of nominal species to a small, monophyletic core of South American acaras built around the type species Cichlasoma bimaculatum; amazonarum is one of seven new species he described in that 1983 work, alongside boliviense, orientale, orinocense, paranaense, pusillum, sanctifranciscense and araguaiense. Kullander himself noted geographic variation across the species' enormous range, and later commentators (Heijns 2014) have suggested it may eventually be split into several species — a plausible outcome given how widely it is distributed.
Morphology
This is a small-to-medium acara, deep-bodied and laterally compressed in the typical Cichlasoma mould. FishBase gives a maximum of about 5.5 in standard length, with a published maximum weight near 116 g — a fish of perhaps 6.5–7 in in total length at the largest, but most individuals are smaller. The base colour is an unassuming brassy-grey to olive that turns dull when the fish is stressed or out of condition; this drabness is part of why the species was long overlooked and confused with its relatives. The diagnostic markings are a single dark blotch on the midflank, flanked by two short vertical white bars — a pattern that aquarists have compared to the keyhole cichlid, Cleithracara maronii — together with a second dark spot at the base of the caudal fin. The species is at its best in breeding dress: the flanks darken and contrast sharpens, and the lower jaw and the lower part of the gill cover flush a rich dark red. Sexual dimorphism is modest and typical of the genus — males grow somewhat larger and develop more pointed, extended soft dorsal and anal fins, while ripe females are rounder and deeper-bodied — but the sexes are not reliably told apart outside of breeding condition. Because the genus is notoriously difficult to identify without locality data, body proportions and meristics rather than colour are what separate amazonarum from the other Amazonian Cichlasoma.
Habitat
Cichlasoma amazonarum is a lowland Amazonian fish with one of the broadest ranges in its genus. It occurs along the mainstream of the Amazon-Solimões from the upper drainages in Peru — the Ucayali, Huallaga, Yavarí and the upper Amazon near the type locality on the Ampiyacu — eastward through Colombia and across Brazil to the river's mouth near Gurupá, with records also from French Guiana and the coastal drainages of Amapá in northern Brazil. The Catalog of Fishes and the IUCN extend the range to Bolivia and questionably to Ecuador. Within this vast area it is a fish of still and slow water: FishBase records it from coastal swamps and seasonally flooded grounds, and it occupies floodplain lakes, marshes, oxbows and inundated forest rather than the open river channel. These are shallow habitats — typically the upper metre or few metres of the water column over soft, often leaf-littered or muddy bottoms. The water is warm and on the soft, mildly acidic side: FishBase gives a preferred range of pH 6.0-7.0 and roughly 72–81 °F, with hardness up to about 15 °dH, consistent with the broad chemical tolerance one expects of a wide-ranging floodplain generalist. The enormous geographic spread means the species spans whitewater, clearwater and the margins of blackwater systems.
Feeding
Cichlasoma amazonarum is a small generalist omnivore that forages over and within the soft bottom of quiet floodplain waters. FishBase places it low on the food web, with an estimated trophic level near 2.5, consistent with a diet of small benthic invertebrates, insect larvae, detritus and incidental plant and seed material taken from the sediment and leaf litter. It is not a specialised sand-sifter like the eartheaters, nor a piscivore; it is the kind of opportunistic mid-sized acara that works the bottom and lower water column for whatever small live food and organic matter it can find. In aquaria it accepts essentially anything offered — quality flake, frozen bloodworm, and even beef heart have all been used as conditioning foods — which mirrors the catholic, low-trophic feeding of the wild fish. In its floodplain communities it functions as one of many small generalist cichlids partitioning the invertebrate and detritus resources of seasonally inundated habitats.
Mating
Like the other true Cichlasoma, amazonarum is a monogamous pair-forming substrate spawner whose reproduction is built around a jointly defended territory. Outside of breeding the fish are loosely social and notably adaptable in temperament — keepers describe them as mild among mild tankmates and pugnacious among pushy ones, and as responsive, almost personable fish that learn to recognise their keeper in the manner of an oscar. When a pair forms, the two fish display to one another more or less constantly, stay close together, and chase intruders out of a chosen patch of bottom. As spawning approaches the mutual display intensifies and the pair begins cleaning a spawning surface, usually a flat stone; given a choice they prefer a near-vertical or upright rock, though horizontal sites are also used. The principal danger at this stage is intraspecific: two males or an unsettled pair can fight savagely, and one keeper recorded rival males jaw-locking until they tore each other's lips and jaws apart. A well-matched pair in adequate space, however, settles into the textbook biparental routine.
Breeding
Cichlasoma amazonarum is a biparental open substrate spawner, and a famously prolific one in captivity. The eggs — a typical spawn runs to roughly 300-500 small amber eggs — are laid in a tidy circular patch on the cleaned spawning surface, most often an upright or near-vertical flat stone. At about 81 °F (80 °F) the eggs hatch in approximately 60 hours, and the wrigglers become free-swimming roughly five days after that. Care follows the classic substrate-spawner division of labour: the female stays with the eggs and larvae, fanning and tending the brood, while the male patrols and defends the surrounding territory. The fry grow quickly and take newly hatched brine shrimp and prepared foods eagerly, and well-conditioned pairs spawn again and again — keepers report the species so reliably productive that captive-bred fry are a fixture at aquarium-society auctions. No detailed account of wild spawning exists, but there is no reason to think the natural behaviour differs in essentials from this captive picture, which matches the open-substrate, biparental mode of the genus as a whole.
In the aquarium
Cichlasoma amazonarum has a long, if quiet, history in the hobby and is among the easier New-World cichlids to keep and breed — but it is sold under so many names (and confused with so many relatives) that the first challenge is simply knowing what you have. A pair is comfortably housed in a tank of around 30–35 US gal for breeding, with more room welcome if the fish are kept in a community or a group from which a pair is allowed to form. The published keeping accounts describe exactly the setup the fish appreciates: a layer of sand or fine gravel, driftwood, hardy plants such as Vallisneria, Ceratopteris and Echinodorus with some floating cover, and several flat rocks laid flat or propped upright against the glass to serve as spawning sites. Filtration with a canister and consistent water changes keep the water clean; the fish are not demanding about chemistry, doing well in moderately soft, slightly acidic to neutral water that mirrors their floodplain origins (pH around 6.0-7.0, temperature about 75–82 °F), though they tolerate harder water than that.
Feeding is trouble-free — good flake, frozen bloodworm and similar foods, offered a couple of times a day in amounts eaten within a few minutes, keep them in colour and condition. The temperament is the one thing to plan around. These acaras are peaceful enough toward dissimilar tankmates and make good company for fish like firemouths (Thorichthys meeki) or other medium cichlids, and they benefit from a dither or target fish at breeding time to redirect their aggression outward. The real risk is between conspecifics: rival males and mismatched pairs can fight to serious injury, so a group should be given space to sort out a pair, and a divider kept handy is prudent. For an aquarist who wants an adaptable, responsive, readily spawned South American cichlid that does not grow large, amazonarum is an excellent and underrated choice — provided it is bought for what it is rather than under a misleading trade label.
Conservation
The IUCN Red List assesses Cichlasoma amazonarum as Least Concern (assessed 10 November 2020 by R.G. Frederico, current in the 2025 update), with a stable population and no documented threats — an unsurprising verdict for a habitat generalist spread across essentially the entire Amazon lowland and into the Guianas. The assessment notes no specific pressures on the species. It carries no CITES or CMS listing. FishBase records it as of minor commercial fisheries value and of commercial value in the aquarium trade, and several regional checklists list it explicitly as an ornamental fish; harvest for the aquarium and food trade is at a level that the conservation assessment does not flag as a concern. As with every wide-ranging Amazonian fish, the relevant long-term backdrop is the basin-wide intensification of dams, deforestation, mining and altered flood-pulse hydrology degrading Amazonian freshwaters generally, but none of these is documented as a present danger to this particular, abundant and adaptable cichlid. (Note that the Cichlid Room Companion species page still describes the fish as not evaluated, a record that predates the 2020 Red List assessment.)