Taxonomy & naming
Charles Tate Regan described this fish in 1913 in 'The fishes of the San Juan River, Colombia' (Annals and Magazine of Natural History), naming it Cichlosoma (Aequidens) biseriatum — though Eschmeyer's Catalog of Fishes notes the original genus should properly have been spelled Cichlasoma. The type locality is the Río Condoto, a tributary of the Río San Juan in northwestern Colombia. Seven of the eight original syntypes survive at the Natural History Museum, London, as BMNH 1913.10.1.80–88. Eigenmann moved the species to Aequidens in 1923, and there it stayed for the better part of a century — Kullander still listed it as Aequidens biseriatus in the 2003 Checklist of the Freshwater Fishes of South and Central America.
The modern placement comes from Musilová, Říčan and Novák (2009), whose phylogeny of the cichlasomatine cichlids showed that the trans- and cis-Andean acaras of the rivulatus group are not true Aequidens. They erected the genus Andinoacara for them, and the Catalog of Fishes, FishBase and GBIF now all treat the species as Andinoacara biseriatus (Regan, 1913), with Aequidens biseriatus as a synonym. The genus name marries andino, for the Andes on whose flanks and valleys these fish live, to acará, the Tupí-Guaraní word for cichlids. Within Andinoacara, biseriatus belongs to the rivulatus assemblage alongside the green terror (Andinoacara rivulatus) and the Pacific-Peruvian Andinoacara stalsbergi; it was the side-by-side comparison with Andinoacara stalsbergi, described the same year, that pinned down several of its diagnostic features. The later revision by Wijkmark, Kullander & Barriga Salazar (2012), which redescribed Andinoacara rivulatus and named Andinoacara blombergi from Ecuador, did not re-examine biseriatus but continued to recognise it as valid. The species has no established English common name; a Portuguese database label, 'acará-de-San-Juan,' nods to its home river but is not in real use.
Morphology
This is a small, stocky, deep-bodied acara, compact by the standards of its genus. FishBase (from Kullander, 2003) gives a maximum of about 3 in total length for males and unsexed fish and roughly 4.5 in for females, while the German aquarium literature (Stawikowski & Werner, 1998) reports up to 6.5 in; keepers describe adults in the 3–4.5 in range. Either way it is one of the smallest described species in Andinoacara, a long way short of the green-terror bulk many hobbyists expect from the genus.
The colour pattern is variable, and it is what the original describer keyed on. The body can be uniformly dark or marked with dark longitudinal stripes and rows of spots running along the scale rows, and paler fish also show vertical cross-bars. A dark blotch sits on the flank, a smaller spot at the base of the tail, and a blackish spot or ocellus in the dorsal fin between roughly the tenth and twelfth spines. The dorsal fin carries a pale edge over a dark submarginal stripe, the soft dorsal and caudal are spotted, and the lower fins are dark-edged. Musilová and colleagues (2009) separated biseriatus from its close relative Andinoacara stalsbergi by a tidy set of characters: nape scales rimmed with dark pigment, a dark dot in the centre of each body and opercle scale rather than dark scale edges, a narrow reddish margin on the caudal fin instead of a broad whitish one, a lateral spot set higher on the flank, and an extra dorsal-fin spot — more prominent in females — above the bar that carries the lateral spot. The trait behind its name is on the face: Regan found it 'frequently' has only two rows of scales on the cheek, where Andinoacara stalsbergi has three. Sexual dimorphism is modest and typical of substrate-spawning acaras — females run smaller and show that supernumerary dorsal-fin spot more strongly — but documented differences beyond size and the female's slightly showier dorsal marking are thin in the literature.
Habitat
Andinoacara biseriatus is endemic to Colombia, and to one of the wettest corners of the Neotropics: the Chocó. The Catalog of Fishes and FishBase place its range in the Atrato, San Juan and Baudó basins on the Pacific coast, while the IUCN assessment adds the Dagua and frames the whole distribution as spanning both slopes — the Atrato drains north to the Caribbean, and the San Juan, Baudó and Dagua run west to the Pacific. The type locality, the Río Condoto, is a San Juan tributary. GBIF's georeferenced records — drawn heavily from Colombian collections such as the Colección Hidrobiológica del Chocó and the Valle del Cauca surveys of the Anchicayá, Calima and Dagua — bear out a range concentrated in the lowland Pacific drainages, with data running back to a 1912 collection.
This is a fish of running water: the IUCN describes it from creeks and rivers, and FishBase classes it as benthopelagic in rivers. The in-situ chemistry fits the soft, acidic, fast-draining streams of the Chocó rainforest — FishBase records a pH of about 5.5–6.7 and very soft water (around 0–3 °dH), with a reported temperature band of roughly 75–84 °F, though that last figure traces to the aquarium literature and may reflect tank rather than field conditions. Beyond these few numbers little has been published on its preferred microhabitat — substrate, cover, depth — so the honest answer is that the natural history of this species is poorly documented.
Feeding
There is no published diet study for Andinoacara biseriatus, so what can be said comes from its genus and from general acara biology. FishBase assigns it a modelled trophic level of about 3.2 — the value expected of a small generalist that leans carnivorous rather than a specialist — and aquarium accounts treat it as a straightforward omnivore that takes prepared foods readily alongside live and frozen invertebrates. Like other members of the rivulatus group, it is built to forage over the bottom of its stream, picking at and sifting small invertebrates, and it will take vegetable matter as well. Without gut-content or stable-isotope work from the wild, that picture is reasonable inference from close relatives rather than a documented account of what this fish actually eats in the Chocó.
Mating
Specific courtship and pair-formation behaviour for Andinoacara biseriatus has never been described in the scientific literature. What is known is the genus-level pattern: Andinoacara, like all Cichlasomatini, are substrate-spawning, biparental cichlids that form pairs rather than harems. Hobbyist observations fill in the broad strokes and fit that mode — the fish are stocky and notably pugnacious for their size, grow more aggressive and territorial as they mature, and do best as a single fish or a settled mated pair rather than crowded. That temperament, the family resemblance to the 'terror' acaras, implies the usual routine of a male and female establishing and jointly defending a spawning territory. But the mechanics of how pairs form, the courtship displays, and any size-assortative pairing remain unrecorded for this species and should be read as expectation, not documentation.
Breeding
Andinoacara biseriatus is a substrate-spawning, non-mouthbrooding cichlid with biparental care — the reproductive mode of all Cichlasomatini, as Musilová and colleagues note. FishBase records that it spawns up to about 120 eggs, laid on flat stones, with both parents tending the eggs and larvae. This is the standard acara strategy: the adhesive eggs are deposited on a cleaned hard surface, the female fans and guards the clutch while the male holds the perimeter, and the free-swimming fry are then shepherded as a school. Aquarium video of the species spawning exists, and it has been bred in captivity, but no detailed study of clutch development, fry growth or breeding triggers has been published for either wild or tank fish. The egg count and the flat-stone substrate are the firm facts; the rest follows from its place in a well-known group rather than from observation of this particular fish.
In the aquarium
Andinoacara biseriatus is a genuine rarity in the hobby. It enters the trade only sporadically — almost always as a small consignment of wild-caught Colombian imports, or from the few specialist breeders keeping it going — so tracking one down outside a handful of dedicated cichlid networks takes patience. The nickname 'bronze terror,' coined by Practical Fishkeeping contributor Max Pedley in the magazine's February 2021 issue, captures it well: a small cichlid with the pugnacity you would expect from its larger relative the green terror, growing more assertive and territorial as it matures. It is rated intermediate in difficulty — undemanding once settled in the right chemistry, but exacting on space, tankmate choice, and simply being found.
Tank: a single fish or a settled mated pair is the practical unit. Andinoacara.com, which has kept and bred the species, recommends a minimum footprint of four feet (roughly 30 US gal) even for a pair, since crowding brings out the worst in them; a larger aquarium of 40–50 US gal gives a pair room to hold territory and takes the edge off aggression. Use a fine sand substrate to suit its benthic origins and its habit of rooting on the bottom, add flat stones or smooth slate for spawning surfaces and territorial dividers, and break up sightlines with driftwood and leaf litter — both at home in the soft, acid Pacific-slope drainages.
Water: keep it very soft and acidic, matching the wild streams — pH 5.5–6.7 and hardness to roughly 3 °dH, with temperature in the 75–81 °F range. Efficient biological filtration with moderate flow suits a Chocó stream fish; strong tumbling currents are not needed.
Tankmates: choose carefully. Andinoacara.com warns that any fish small enough to fit in the mouth is at risk, so this is not a standard community fish. Robust dither species that hold their own work best — large characins such as bleeding-heart tetras (Hyphessobrycon erythrostigma) and bottom-dwellers like Corydoras catfish (Corydoras spp.) or bristlenose plecos (Ancistrus spp.) are the pairings experienced keepers recommend. Other medium-bodied South American cichlids can work in a spacious tank, but a second pair of acaras needs close monitoring, and aggression spikes around a spawn — make sure any tankmates have retreats. Given its rarity and Vulnerable status, captive-bred stock is the better choice whenever it can be found.
Conservation
The IUCN Red List assesses Andinoacara biseriatus as Vulnerable under criterion B1ab(iii) (Villa-Navarro, Mesa-Salazar & Sanchez-Duarte; assessed 8 October 2014, published 2016). The listing rests on a small, restricted range — an extent of occurrence of about 19,224 mi² in the Chocó, broken into roughly five locations defined by the threats it faces — together with a continuing decline in habitat quality. The assessors call it a rare species and could not estimate its population size or trend. It is not used commercially, though it does turn up in the international aquarium trade in modest numbers.
The specific pressure is gold and platinum mining, which has scarred the Chocó's rivers for decades. Dredging and alluvial mining pour sediment into the streams and release pollutants — historically including mercury — degrading exactly the soft, clear, fast-flowing water Andinoacara biseriatus depends on. The IUCN flags increased sedimentation and reduced water quality from mining as the operative threats, and notes that the species occurs in no protected area and has no conservation measures in place. As a narrow-range endemic of disturbed lowland drainages, it is a textbook case of a fish endangered not by collection but by what is being done to its watershed. The honest caveat is that the assessment is now over a decade old and annotated as needing updating, and that, as the assessors stress, the basic data on its numbers and on the real impact of mining have yet to be gathered.