Taxonomy & naming
The British ichthyologist Charles Tate Regan described this fish in 1906, placing it in the now-defunct genus Heterogramma — so the original combination is Heterogramma commbrae Regan, 1906. Regan was then sorting out the small cichlids of the La Plata basin; the genus Apistogramma, into which the species was later moved, was not erected until his own 1913 revision. Both FishBase and the Catalog of Fishes carry commbrae as a valid Apistogramma in the subfamily Geophaginae, the geophagine or eartheater radiation. The IUCN lists Heterogramma commbrae Regan, 1906 as the only synonym; a near-simultaneous name, Heterogramma corumbae Eigenmann & Ward, 1907, is the other half of the story.
That odd spelling has a well-documented origin. The German-American ichthyologist Carl H. Eigenmann had recognised the species first, from specimens taken at the city of Corumbá in Mato Grosso do Sul, southwestern Brazil, and meant to name it Heterogramma corumbae for the town — but his description did not appear until 1907. Regan, working a year earlier from material collected at two other upper-Paraguay localities, received labelled photographs from Eigenmann and adopted the intended name; along the way 'corumbae' was garbled into 'commbrae,' apparently a simple misreading. Because Regan's 1906 name was published first, the rules of zoological nomenclature fix the misspelling as valid, and Eigenmann's correctly-spelled corumbae (1907) fell as a junior synonym. The type material came from the upper Paraguay watershed, with type localities recorded as 'Carandasiñho, Mato Grosso' and 'Colonia Risso.' Sven O. Kullander, the foremost modern reviser of the genus, later monographed the species in 1982.
In Mike Wise's widely used framework on apistogramma.com, Apistogramma commbrae anchors the Apistogramma commbrae-complex, a cluster of mostly tiny species that seem to be offshoots of the Apistogramma resticulosa-complex, all nested within the broad Apistogramma regani-lineage — the lineage diagnosed by a full set of four infraorbital and five dental head pores and by the lack of a distinct lateral spot on the third vertical bar. The hallmark of the complex, and the easiest field mark here, is the double caudal-peduncle blotch, formed where the caudal spot merges with a heavily pigmented part of the seventh body bar. The species also carries the provisional trade codes A93 and A94, which hobbyists use to track geographic forms before formal study resolves them.
Morphology
This is one of the smallest cichlids in a genus already full of dwarfs. FishBase gives a maximum of about 1.5 in standard length for males and roughly 1.5 in total length for females; aquarium sources report males closer to 2 in and females near 1 in, so most fish in hand fall in the 1–2 in range, with the females noticeably stunted relative to the males. The body is short, fairly deep, and laterally compressed — compact and unspectacular next to the high-finned showpieces of the genus.
The defining mark is the double caudal-peduncle spot: a pair of dark blotches at the tail base where the caudal spot fuses with the rear body bar. Shared across the Apistogramma commbrae-complex, it is the single most reliable way to tell these fish from their congeners. The flank usually carries a lateral band that breaks into a row of spots rather than a continuous stripe, in keeping with the Apistogramma regani-lineage, and some populations show horizontal abdominal striping. The species can be polymorphic, and some males develop red and blue markings on the cheeks together with a yellow gular (throat) region. Dimorphism is clear: males are larger, more colourful, and longer-finned, while females are smaller and plainer out of season. In spawning condition and during brood care, though, the female transforms — taking on a bright yellow ground colour with bold black body and face markings and black on the leading edge of the pelvic fins, the universal signal of a guarding Apistogramma mother.
Habitat
Apistogramma commbrae lives at the far southern edge of the apisto range, in the Paraguay, lower-to-middle Paraná, and Uruguay basins. Its core is the Paraguay River watershed above the confluence with the Salado, spanning Argentina, Bolivia, Brazil, and Paraguay; there is also a recorded population in the upper Guaporé River of western Brazil, a Madeira tributary that belongs to the Amazon system rather than the La Plata drainage. The IUCN maps it across Argentina (Entre Ríos, Misiones, Chaco, Corrientes, Formosa, Santa Fé), Bolivia, Brazil (Mato Grosso, Mato Grosso do Sul, Paraná, Rio Grande do Sul, Santa Catarina), and Paraguay, with Uruguay listed as possibly present, and estimates an enormous extent of occurrence of about 1.54 million km². GBIF and the regional literature also flag it as a possible non-native in the upper rio Paraná above the former Sete Quedas falls, where its recent appearance may trace to the flooding of that barrier by the Itaipú reservoir.
In the wild it turns up in everything from large rivers to small streams and seasonal floodplains, but always in the shallows, favouring margins thick with aquatic and riparian vegetation, often with floating plants overhead. The IUCN summary describes it as typically in standing water with vegetation — estuaries, streams, swamps, marginal lagoons, plains, and sinuous oxbow lakes rich in submerged and floating plants, frequently in dammed or impounded settings. Its water chemistry sets it apart from most of the genus: where the great majority of Apistogramma demand soft, acidic blackwater, Apistogramma commbrae is often found in neutral to slightly alkaline water (in-situ and aquarium-relevant ranges run from about pH 6 to 7.4) and tolerates moderate hardness. Living so far south, it also meets real seasonal swings, with winter cold spells reportedly pushing temperatures toward 61 °F — well below the tropical comfort zone of its equatorial relatives. FishBase lists a preferred band of about 73–82 °F.
Feeding
Like the rest of its genus, Apistogramma commbrae is a micropredator — a small, benthic-leaning carnivore that works the substrate and leaf litter for invertebrate prey. FishBase places it at a trophic level near 3.2, and the IUCN habitat summary lists its diet as worms, crustaceans, and insects. In nature these dwarf cichlids glean chironomid larvae, microcrustaceans, and other small benthic and interstitial animals from among sand, detritus, and decaying plant matter, picking selectively rather than bulk-sifting. The vegetation-choked shallows it prefers are exactly the kind of structurally complex microhabitat that concentrates that sort of small invertebrate life. In aquaria it readily takes live and frozen foods — Artemia, Daphnia, Moina, and bloodworm — and, unlike many fussier congeners, will learn to accept prepared pelleted foods, part of the broader hardiness that makes it an unusually easy apisto to keep.
Mating
Apistogramma commbrae appears to be essentially monogamous, a male seldom holding more than one female at a time — a contrast to the harem polygyny common elsewhere in the genus, and probably tied to its small size and the modest territories it defends. The pair bond runs along what the hobbyist literature calls a 'patriarch-maternal' line: the female gives close, hands-on care to the eggs and young inside a chosen cave, while the larger male patrols and defends the outer boundary of the territory against rivals and intruders. Pair formation and spawning centre on a suitable cavity — a crevice among roots, rocks, or leaf litter, or in the aquarium a flowerpot, length of pipe, or other dark recess. The female's dramatic shift into bright yellow-and-black livery is both a courtship display and a brood-defence signal, advertising her readiness and her occupied nest. Because the fish comes from a strongly seasonal subtropical climate, its reproductive rhythm is tied to the warm-season window rather than to the year-round spawning available to equatorial apistos.
Breeding
Apistogramma commbrae is a cave (substrate) spawner with female-dominated brood care — the classic Apistogramma reproductive mode. The female deposits her eggs on the ceiling of a cave or crevice; FishBase reports a maximum of about 80 eggs, a small clutch in keeping with the fish's small size. She is the primary clutch-tender, fanning and guarding the eggs and then shepherding the larvae after they hatch, though the male often helps with eggs and larvae and consistently defends the surrounding territory. Depending on temperature, the eggs hatch in roughly 36–72 hours, and the fry become free-swimming a few days later.
Temperature carries a practical quirk for this cool-water species. Above about 77 °F the newly free-swimming fry can emerge too small to take even newly hatched Artemia nauplii as a first food — a problem breeders solve by keeping the spawning and rearing water cooler. Slightly acidic water, around pH 6.5, favours egg development and fry survival, but it should not be pushed too low or juvenile losses climb. For all its adult tolerance of harder water, then, the species still breeds best in the soft, mildly acidic conditions typical of the genus, and its broad acceptance of parameters plus its cool-tolerance make it one of the more forgiving Apistogramma to bring into spawning condition.
In the aquarium
Apistogramma commbrae is uncommon in shops — imported far less often than flagships like Apistogramma cacatuoides or Apistogramma borellii — but it has a loyal following among dwarf-cichlid keepers precisely because it forgives what most of the genus will not.
Water: where most Apistogramma insist on soft, acidic blackwater, this species comes from the neutral-to-slightly-alkaline floodplains and lagoons of the La Plata system and shrugs off moderate hardness. A working range of pH 6.0–7.4 and 68–79 °F covers essentially any domestic tap supply once aged, so no reverse-osmosis or peat-softened water is needed for healthy adults. Spawning is another matter — it runs most reliably in soft, slightly acidic water around pH 6.5 — so breeders should nudge the chemistry downward.
Tank: 15–20 US gal suits a pair or small group, and a longer footprint of 31.5 in or more lets the male hold a territory without constant skirmishing. Keep flow gentle; this is not a river-rapid fish, and strong current stresses it.
Aquascape: mirror the vegetated shallows it comes from. Use a sand bottom for its rooting and digging, a generous scatter of dried leaf litter (Indian almond, oak, or equivalent) for cover, tannins, and the biofilm that feeds first-days fry, and dense planting with Java fern, Anubias, Vallisneria, and floating cover. Spawning caves are essential — flower-pot halves, short PVC or bamboo, coconut shells, and overhanging stones all work.
Food: as an obligate micropredator it feeds best on live and frozen invertebrates — Artemia nauplii and adults, Daphnia, Moina, bloodworm — but, unusually, it will also take good dried micro-pellets and granules once established. Feed small amounts two or three times a day rather than one large meal.
Tankmates: because a male seldom courts more than one female, a bonded pair in a species tank or lightly stocked community is the standard approach. Dither fish calm the pair's nerves — pencilfish (Nannostomus spp.), small tetras from the same region (a cautious nod to the Buenos Aires tetra, watching its size), or similarly sized Corydoras all serve. Avoid boisterous or fin-nipping tankmates, which target the male's finnage and harass a cave-bound female, and keep other Apistogramma out unless the tank is large and clearly zoned, since males will fight.
Common mistakes: sexing is easy once a female colours up — see Morphology for the full size-and-colour split — but out-of-condition females are drab and brownish and are often taken for a different species or a sick fish before their yellow-and-black transformation. The usual errors are running the water too warm (above 79 °F brings fry-stage trouble and blunts the cool-season conditioning this subtropical fish benefits from), skimping on caves and leaf litter (a female with no spawning site stays chronically stressed), and leaving the fish in hard, alkaline municipal water without adjustment — survivable for adults but consistently fatal to eggs and early fry. Given the right setup, it is one of the best starter apistos for keepers ready to move past the most common trade species.
Conservation
The IUCN Red List assesses Apistogramma commbrae as Least Concern (assessed 28 October 2020; assessment by R. G. Frederico, reviewed by T. J. Lyons, published in the 2025 update). The rationale is straightforward: despite little species-specific information, the fish ranges very widely across the Paraguay, Paraná, and Uruguay basins — an estimated extent of occurrence of about 1.54 million km² — and faces no known direct threats, so it clears the bar for Least Concern even though its population trend is recorded as unknown and it is described as uncommon where it occurs. It carries no CITES listing and is of no fisheries interest, though it is a modest presence in the ornamental-aquarium trade, mostly as wild-caught stock, and the assessment notes that it occurs within at least one protected area.
The broader pressures on its habitat are those of the heavily developed La Plata system: the damming and impoundment of the Paraná and Paraguay rivers (the same engineering that may have let the fish colonise the upper Paraná as a non-native), along with agricultural runoff and wetland modification across one of South America's most intensively farmed regions. For now, a huge range, ecological flexibility, and tolerance of disturbed and impounded waters keep Apistogramma commbrae well clear of conservation concern — by apisto standards, a generalist survivor.