Taxonomy & naming
The black acara carries one of the longest and most tangled nomenclatural histories of any cichlid. It was named by Carl Linnaeus himself, in the tenth edition of Systema Naturae in 1758 — but as Labrus bimaculatus, a wrasse, with the type locality erroneously given as 'In Mediterraneo,' the Mediterranean Sea. The unique holotype (NRM 7, in the Swedish Museum of Natural History) was later shown by Fernholm and Wheeler (1983) to be a South American cichlid from Brazil, not a marine labrid at all. The name was therefore shuffled into Cichlasoma, the genus William Swainson erected in 1839 — and because Swainson had implicitly built that genus on this very fish, bimaculatum is its type species. To settle decades of confusion (Linnaeus's name could otherwise have been claimed by a real Mediterranean wrasse), the International Commission on Zoological Nomenclature issued Opinion 1954 in June 2000, formally fixing bimaculatus as the type species of Cichlasoma and as a cichlid, and placing the name on the Official List. Several junior synonyms attach to it: Sparus filamentosus Gronow in Gray 1854 and Acara gronovii Heckel 1840, both from Suriname. The pivotal modern work is Sven O. Kullander's 1983 monograph, A Revision of the South American Cichlid Genus Cichlasoma. Kullander restricted Cichlasoma to a tight group of generalized, 3-to-6-anal-spined 'acaras' centred on bimaculatum (orinocense, amazonarum, sanctifranciscense, dimerus, portalegrense and kin), and in doing so stripped the name away from the roughly hundred Central American 'Cichlasoma' to which it had been loosely applied for a century — those fish are now spread across Amphilophus, Vieja, Herichthys, Thorichthys and other genera. The hobby took years to absorb the change, and older aquarium literature still uses 'Cichlasoma' in the broad, obsolete sense.
Morphology
Cichlasoma bimaculatum is a moderately deep-bodied, laterally compressed cichlid of unflashy aspect — exactly the generalized 'acara' body plan that anchors the genus. Reported size varies widely with source and with how length is measured: FishBase lists a maximum of about 12 in total length, but this is at the extreme upper end and likely reflects exceptional or cultured fish; wild specimens are far smaller, with USGS and Kullander citing roughly 4.5 in standard length as typical, and most aquarium fish maturing well under 6 in. Ground colour ranges from olive-brown to grey, paler below, often overlaid with iridescent green or blue speckling on the flanks and face and a scattering of dark, broken vertical bars that the fish can intensify or mute with mood. The diagnostic markings — and the source of the epithet bimaculatum, 'two-spotted' — are a single dark blotch set roughly midway along each flank and a second spot at the base of the tail. Breeding and dominant fish darken dramatically, the body taking on the smoky, near-black cast that gives the species its English name. Sexual dimorphism is modest but real: males grow larger and develop more produced, pointed tips to the dorsal and anal fins, while ripe females are rounder-bellied; outside spawning the sexes are otherwise hard to separate. The fish is built much like the 'port cichlid' (true Aequidens portalegrensis) it long sat beside in the trade — the classic field separation is the anal-spine count, with bimaculatum usually carrying four or more hard anal rays against the three of portalegrense.
Habitat
The black acara is a fish of the warm, lowland coastal drainages of northern South America. Its native range, as resolved by Kullander's revision and the Catalog of Fishes, spans the Guianas and adjacent basins: the Essequibo of Guyana eastward through Suriname and French Guiana to the Sinnamary River, the Caroní and lower Orinoco system of Venezuela, and the Rio Branco drainage of the northern Amazon basin, with records extending into parts of Brazil, Bolivia and Peru. It is emphatically a fish of slow and standing waters — canals, ditches, swamps, marshes, oxbows, weedy lagoons and the sluggish margins of streams — rather than fast or open river channels. This is a hardy generalist by the standards of Neotropical cichlids: it favours soft, slightly acidic to neutral water (FishBase gives roughly pH 6.5–7.0 with moderate hardness) but tolerates a broad envelope, copes with warm temperatures in the mid-20s Celsius and above, and is notably tolerant of low dissolved oxygen, an adaptation that lets it thrive in the stagnant, vegetation-choked habitats that exclude more demanding fish. It lives shallow, typically in the upper metre or two of weedy, soft-bottomed water. That ecological flexibility — a tolerance for disturbed, low-quality, warm water plus opportunistic feeding and strong parental care — is precisely what has made it such a successful colonist beyond its range.
Feeding
Cichlasoma bimaculatum is a generalist omnivore with a pronounced ontogenetic diet shift. Studies of young fish in the Sinnamary River of French Guiana by Mérigoux and Ponton (1998) found juveniles working the bottom and water column for small crustaceans, aquatic insect larvae (chironomids and the like) and other micro-invertebrates, taken from among leaf litter, sediment and submerged vegetation. As the fish grow, fish prey become an increasing part of the diet, so that large adults are effectively micro-predators that will take small fishes and fry alongside invertebrates, detritus and incidental plant material. FishBase places its trophic level around 3.6, consistent with this mixed invertivore-to-piscivore feeding mode. In the wild community it is a mid-level opportunist of the still-water margins; in its introduced Florida range, juvenile black acaras have been observed massing around the nests of spawning bluegill (Lepomis macrochirus) and aggressively raiding the eggs — a vivid illustration of how readily this adaptable forager exploits whatever the habitat offers.
Mating
Like the other true Cichlasoma, the black acara is a monogamous, biparental cichlid that forms a pair bond to reproduce. Pairs typically form from a group as fish mature and sort out dominance, and a settled pair stakes out and defends a territory centred on a chosen spawning surface. Courtship follows the familiar substrate-spawner pattern of lateral displays, fin-spreading, jaw-locking trials of strength and cooperative cleaning of the intended spawning site. Colour signals the change of state: both partners, and especially the female, darken markedly as spawning approaches, the flanks taking on the brooding near-black that names the species. Territorial defence is vigorous but the species is not a dedicated bully outside breeding; it is the pair's combined aggression toward intruders near the nest, rather than indiscriminate hostility, that defines its temperament. As with many cichlids kept in confined quarters, a mismatched or forcibly paired couple can turn on each other, so natural pairing from a group gives the steadiest bonds.
Breeding
Cichlasoma bimaculatum is a biparental, open substrate spawner — the ancestral cichlid mode, and the one shared across the restricted genus. The pair cleans a flat, firm surface (a stone, root, broad leaf or, in aquaria, a slab or pot) and the female lays her adhesive eggs in neat rows while the male follows to fertilize them. Clutches are moderate; congeners and reports for this species put a typical spawning on the order of several hundred eggs, scaling with the size of the female. Parental care is shared and committed: the female tends and fans the egg plaque while the male patrols the territory perimeter, and once the eggs hatch the parents move the wrigglers to pits dug in the substrate, shepherding the free-swimming fry as a tight school and herding strays back with mouthfuls. The young are guarded for some weeks, defended against all comers, and the pair will spawn repeatedly through a season under good conditions — in the warm canals of southeastern Florida the species has been recorded spawning in every month of the year. The eggs and fry are protected by vigilance rather than by any specialized nest architecture, the straightforward but effective reproductive strategy that, combined with the fish's hardiness, underlies its success as a colonist.
In the aquarium
The black acara is an easy, almost bombproof cichlid — historically a staple of the trade (often under the muddled name 'port cichlid') precisely because it asks so little. It is not a beauty in the way a peacock or a discus is, and its colours are subtle, which is the main reason it has fallen out of fashion; but as a durable, characterful, breedable cichlid it has few peers among beginner New World fish.
A single pair is comfortable in a tank of around 30–40 US gal, with more room appreciated for a group or a community. Provide a soft or fine-gravel substrate, some rockwork, driftwood and a few flat stones or pots as potential spawning sites, and robust or floating plants — the fish will dig, particularly when breeding, and may uproot delicate plantings. Water chemistry is genuinely undemanding: anything from soft and slightly acidic to moderately hard and neutral suits it (a useful working range is pH about 6.0–7.5, temperature roughly 72–82 °F), and its tolerance of warm, oxygen-poor conditions makes it forgiving of less-than-perfect maintenance. Even so, regular water changes keep it in best colour and condition. It is unfussy at the table, taking quality pellets and flake readily and relishing live and frozen foods — bloodworm, brine shrimp, small crustaceans — with some vegetable matter rounding out the diet.
Temperament is the main thing to plan around. Outside breeding the black acara is reasonably peaceful and can be kept with robust, similarly-sized tankmates — larger tetras and characins, other medium cichlids, catfish — but small fish that fit in its mouth are at risk from adults, and a breeding pair becomes assertively territorial and will clear a wide radius around the nest. It is hardy enough for a beginner's first cichlid and breeds with little encouragement, which makes it an excellent fish for learning cichlid parental behaviour. The one genuine caution lies outside the tank: this is a proven invasive, and it should never be released or allowed to enter natural waters in any warm region.
Conservation
The IUCN Red List assesses Cichlasoma bimaculatum as Least Concern, in an assessment dated 10 November 2020 (current on Red List version 2025-2). The species is widespread across the coastal lowlands of the Guianas, the Orinoco and the Rio Branco, abundant within that range, and ecologically flexible — a tolerant habitat generalist rather than a narrow-range endemic — so it faces no recognized threat of extinction and carries no CITES listing. If anything, the conservation story runs the other way: introduced through aquarium-fish-farm escapes and releases, the black acara has been established in the canals of southeastern Florida since the 1960s, where it is among the most abundant non-native fishes and is regarded as a competitor with native sunfishes for spawning space and an opportunistic raider of their nests. United States risk-screening agencies flag it as a species of concern for further spread in warm climates. Within its native basins it is not a focus of conservation worry, but its presence in Florida is a standing reminder that hardiness and adaptability cut both ways, and that aquarium fish must never be released into the wild.