Taxonomy & naming
The German aquarist-ichthyologist Wolfgang Staeck described Apistogramma acrensis in 2003, in the third volume of his Cichliden-Lexikon (Südamerikanische Zwergbuntbarsche), on page 10. The holotype (MTD F 27040) is held at the Museum für Tierkunde Dresden, with paratypes split between Dresden, the Naturhistorisches Museum Wien (Vienna), and the Museum für Naturkunde Berlin (ZMB 33914); Zarske (2003) catalogued the type series. Eschmeyer's Catalog of Fishes gives the type locality as a lake at the mouth of the Rio Acre, about 16 mi from the city of Rio Branco, in Acre state, Brazil, and treats the name as valid. Before its formal description the fish circulated among hobbyists under provisional labels — 'Apistogramma sp. Rio Acre' and 'Apistogramma sp. Rio Branco' — and it still carries the aquarium catalog code A063.
The genus Apistogramma sits in the subfamily Geophaginae of the Cichlidae, a sprawling South American radiation of more than ninety described species plus a long queue of undescribed forms. Because Apistogramma has never been formally split into subgenera, specialists work from the informal system of lineages, groups, and complexes maintained by Mike Wise on apistogramma.com. In that scheme Apistogramma acrensis falls in the regani-lineage — the assemblage diagnosed by a complete set of four infraorbital and five dental head pores — and, within it, the regani group and the eunotus complex, a cluster of relatively plain, deep-bodied, round-tailed dwarfs typified by Apistogramma eunotus and Apistogramma regani. Past that placement the formal literature is thin: the species was described, illustrated, and listed in Römer's Cichlid Atlas (Römer 2006; Römer & Hahn 2013) and in regional checklists (Sarmiento et al. 2014 for Bolivia), but it has never been redescribed or revised, and its relationships within the eunotus complex remain untested in detail.
Morphology
This is a small dwarf cichlid even by the standards of its genus. Aquarium accounts put adult length at roughly 1.5–2 in, with males reaching about 2 in and females smaller — a size typical of the eunotus-complex dwarfs and well within the range of the genus as a whole. FishBase carries no vouchered maximum length, and no formal meristic description has been published in the open literature, so fin-ray and scale counts specific to Apistogramma acrensis are not reliably available; what follows is drawn from hobby observation and the figures in Staeck's description and Römer's atlas, and should be read as provisional.
In life the fish wears the plain, workmanlike livery of its complex: a moderately deep, laterally compressed body in shades of tan to grey-brown, a dark lateral band running from the snout through the eye to a spot at the tail base, and the abdominal-bar and lateral-spot markings common to the genus. The FishBase name 'Bloodgill dwarf cichlid' points to reddish flushing on the gill cover and cheek of displaying males — the most distinctive bit of colour the species offers. Males also grow the longer, more pointed dorsal and anal fins and the slightly larger body that mark the sex across Apistogramma, and the caudal fin is rounded rather than lyrate or lanceolate, as in the rest of the eunotus complex. Dimorphism is present but modest next to the showier Apistogramma of the cacatuoides or macmasteri groups: females are smaller and plainer and turn bright yellow when they carry eggs or fry, while males are larger, longer-finned, and hold what colour the species has.
Habitat
Apistogramma acrensis is a fish of the southwestern Amazon lowlands. Its documented range is the Rio Acre basin and the upper Rio Purús, straddling the border between Acre state (and adjacent Amazonas) in Brazil and northern Bolivia; the IUCN gives an estimated extent of occurrence of about 147,81 mi², which makes the species reasonably wide-ranging on paper even though actual collection records are sparse. The type locality — a lagoon at the mouth of the Rio Acre near Rio Branco — and the broader regani-group ecology both point to the standard Apistogramma biotope: small, slow forest streams, creek margins, and floodplain pools rather than open river channels.
Few in-situ water measurements have been published, so the chemistry given here is inferred from the range and from the conditions in which hobbyists keep the fish successfully. These are soft, acidic, tannin-stained waters — the tea-coloured blackwater that forms where leaf litter and woody debris break down over sand — with little dissolved mineral content. Aquarium sources converge on roughly pH 5.0–6.5 (closer to pH 4.5 for breeding), very low hardness of about 1–5 dGH, and a warm band of about 73–82 °F. The fish stays close to the bottom among leaf litter, roots, and submerged wood, which supply both cover and the cavities it depends on. This is a picture assembled from the genus and the region rather than from direct field study of Apistogramma acrensis, and should be treated as such.
Feeding
No diet study has been done on Apistogramma acrensis in the wild, so the genus-level picture stands in. Like virtually all Apistogramma, it is a micropredator — a small benthic invertivore that picks tiny animal prey from the substrate and from among leaf litter and biofilm. FishBase places it at an estimated trophic level of about 3.3, a figure modelled from its size and from the diets of close relatives rather than measured from stomach contents. In practice that means small crustaceans (copepods, ostracods, cladocerans), aquatic insect larvae such as chironomids, and other meiofauna sieved or pecked from the bottom and from detritus. In the aquarium the fish readily takes small live and frozen foods — brine shrimp, Moina and Daphnia, microworms, Grindal worms, bloodworms — which matches the micropredatory habit. Its ecological role is the one its whole genus fills across Amazonia: a small, low-level consumer of the invertebrate fauna of leaf-litter and marginal habitats, and in turn prey for larger fishes and birds.
Mating
The reproductive behaviour of Apistogramma acrensis has not been documented in the wild, and little has been published even from aquaria, so the account here is the regani-group and eunotus-complex pattern the species is overwhelmingly likely to follow rather than a record specific to it. Fish of this group are typically harem polygynists: a dominant male holds a comparatively large territory that overlaps the smaller, defended territories of several females, courting and spawning with each in turn while the females do the close-quarters tending. Pair bonds are weak and centred on the female's cave; the male's job is territorial display and defence of the wider area rather than direct brood care.
Courtship in these dwarfs runs on colour and posture. A ripe female intensifies to bright yellow, adopts head-down displays and curving 'S' presentations at the cave entrance, and leads a displaying male toward the chosen cavity, while the male flares his fins and shows off his size and what colour he has. Where a harem is not possible — a small tank with a single female — the pair simply breeds as a couple instead. Without observations specific to Apistogramma acrensis, how fully it expresses harem behaviour in the wild is unconfirmed.
Breeding
Breeding has not been described in the wild for Apistogramma acrensis, and detailed aquarium spawning reports are scarce; what can be said with confidence is the mode shared across the genus and its group. Apistogramma are cave-spawning substrate brooders with female-dominated parental care. The female selects and cleans a concealed cavity — under wood or a root, inside a crevice, or in the aquarium an inverted pot, coconut shell, or snail shell — and lays a clutch of adhesive eggs (typically a few dozen to perhaps a hundred-odd in a small species like this one) on its ceiling or wall, where the male fertilizes them. She then tends the brood almost single-handedly: fanning the eggs, guarding the cavity, and after hatching shepherding the wrigglers and then the free-swimming fry as a tight school near the bottom, herding strays back with her body and mouth while the male patrols the surrounding territory.
Soft, warm, acidic water is the usual trigger and also matters to egg viability in blackwater Apistogramma, which is why hobbyists drop the pH toward 4.5–5 and the hardness near zero to spawn fish of this type. In many Apistogramma such conditions also skew the brood toward males, a well-known temperature- and chemistry-linked effect, though it has not been quantified for Apistogramma acrensis. Free-swimming fry take infusoria and newly hatched brine shrimp as first foods. None of the species-specific numbers — clutch size, egg and fry development times, age at independence — have been reliably published for this species, so they are left unstated here rather than borrowed wholesale from its relatives.
In the aquarium
Apistogramma acrensis is one of the rarer Apistogramma in the hobby, imported sporadically under the code A063 or the trade label 'sp. Rio Acre,' and kept by a comparatively small number of specialists. The major English-language care references have not covered it — Seriously Fish carries no profile — so the honest starting point is this: it is not a beginner fish, and usable published records of its husbandry are thin. What follows is the best reconstruction available from close relatives and the handful of hobbyist accounts that exist.
Tank. As a small dwarf cichlid (males around 2 in) the species does not need a large tank, but it does need a well-structured one. A footprint of roughly 60 × 12 in (about 15 US gal) suits a pair, and 80 × 15.5 in or more is better for a trio or small harem, giving each fish defensible space. Seriously Fish gives 45 × 12 in as a minimum for a pair of the closely related Apistogramma eunotus; that is tight here, given the harem dynamic and the need for several caves in different female territories.
Water — the critical point. This is a blackwater fish from one of the more acidic, mineral-poor corners of the Amazon, and water chemistry is almost certainly the commonest reason keepers fail with it. The maintenance range is pH 5.0–6.5, hardness 1–5 dGH, and temperature 73–82 °F (AquaPortail, drawing on regional data and consistent with the Apistogramma eunotus profile); for breeding, hobbyists on apistogramma.com recommend conditions nearer pH 4.5–5.0 with hardness close to zero, which matches the Breeding section above. Holding pH below 5.5 in a home tank is genuinely hard — in very soft, low-conductivity water even small additions of buffering material or tap minerals push it back up, and standard pH kits read unreliably at that end of the scale. The practical advice is to treat conductivity as the primary metric (target EC around 20–50 µS/cm, TDS around 15–35 ppm), use RO or equivalent low-mineral source water, and bring the pH down naturally with tannin sources — leaf litter, alder cones, oak leaves — accepting that pH itself is hard to pin down precisely in such soft water. Keep all calcareous decor out: limestone, crushed coral, and calcium-based substrates dissolve and harden the water.
Decor and setup. Fine, dark sand is appropriate — it mimics the silty-sandy margins of blackwater creeks, lets the fish sift normally, and keeps the tank dim enough to show it at its best. Multiple caves are essential: inverted ceramic flowerpots, coconut shells, or lengths of PVC pipe all work, and some should be small enough that the male cannot follow the female inside, since she needs a safe retreat during and after spawning. A layer of dried leaves (beech, oak, Indian almond) does double duty — releasing the tannins and humic acids that help the chemistry, and recreating the leaf-litter biotope the fish is built for. Bogwood adds further tannins and hides, moderate planting (Microsorum, Anubias, Cryptocoryne) with some floating cover diffuses the light, and flow should be gentle, since these fish live in still margins, not river channels.
Tankmates and social structure. In nature the species almost certainly forms harems — one male over several female territories — so in a tank of adequate size a group of one male to two or three females is the most rewarding arrangement, provided each female has her own cave and enough broken sightlines that the male cannot constantly harass subordinates. A single pair works in a smaller tank. After spawning the female turns intensely territorial and may attack the male, who sometimes has to be removed. For dither fish, choose small, peaceful species that stay out of the bottom zone — pencilfish (Nannostomus spp.), small tetras such as ember tetras (Hyphessobrycon amandae) or neon tetras, and small Corydoras that will not compete for cave sites. Avoid anything large enough to threaten the adults or disturb spawning, and do not mix in other Apistogramma.
Feeding. No trouble in the aquarium: small live and frozen invertebrates — Artemia nauplii and adults, Daphnia, Moina, Grindal worms, microworms, bloodworms — are taken readily, and most fish learn to accept high-quality micro-pellets in time. Variety across the invertebrate menu beats any single food.
Difficulty and common mistakes. AquaPortail rates the species 'complicado' — an experienced keeper's fish — which is the right framing. The two usual failure modes for blackwater Apistogramma, and almost certainly for this one, are keeping it too hard and too alkaline (it survives at pH 6.5–7 but is unlikely to breed and may not thrive long-term) and trying to spawn it before establishing genuinely ultra-soft, acid conditions. A third is too sparse a setup: without adequate caves and leaf cover the fish stays hidden and stressed, and the female has no safe territory to defend. Given how rarely Apistogramma acrensis reaches the trade and how little husbandry data exists for it, a keeper new to blackwater Apistogramma would do well to cut their teeth on a more commonly kept eunotus-complex species first.
Conservation
The IUCN Red List assesses Apistogramma acrensis as Least Concern (assessor R.G. Frederico; assessed 28 October 2020, published in the 2025 update). The rationale is range over data: although very little is known about the species, it spans a wide area — an estimated extent of occurrence of about 147,81 mi² across the Rio Acre and upper Rio Purús basins in Brazil and Bolivia — and faces no documented severe threats, so the assessors judged it Least Concern despite the thin information base. The population trend is listed as unknown, the fish is described as apparently uncommon, and the assessment explicitly flags the need for basic research on its distribution, life history, and any harvest or trade. It carries no CITES listing.
The wider pressures on this part of the Amazon are the familiar ones for southwestern-Amazon lowland streams: deforestation and the spread of cattle pasture and agriculture around Rio Branco and across Acre, with the attendant siltation, run-off, and loss of the riparian forest that supplies the leaf litter and shade these blackwater creeks depend on. The aquarium trade touches the species only lightly — it is uncommon in the hobby and moved in small numbers, mostly as wild-collected 'A063' or 'sp. Rio Acre' — and is not flagged as a conservation concern. As with much of the genus, the honest summary is that Apistogramma acrensis looks secure mainly because it is widespread and because no one has yet looked closely enough to find a problem.