Taxonomy & naming
Wolfgang Staeck and Ingo Schindler described Apistogramma erythrura in 2008 in the journal Vertebrate Zoology (58(2): 197–206), from fish taken in the río Mamoré system of the Bolivian Amazon. The name joins the Greek erythros (red) and oura (tail) — a plain reference to the red caudal fin most adult males carry. The holotype, an adult male of 1.5 in SL, was collected at Laguna Larga (Lago Largo) in the drainage of the río Yata, roughly 99 mi northwest of Santa Ana de Yacuma in Bolivia's Beni department; it sits with the paratype series in the fish collection of the Museum für Tierkunde Dresden (MTD F 31469).
The species belongs to the Apistogramma trifasciata group within the tribe Geophagini (subfamily Cichlinae). Its closest relative is Apistogramma trifasciata, and the clearest difference is what erythrura lacks: the dark oblique stripe running from the pectoral base to the anal-fin origin that marks trifasciata. The describers backed this with fine detail — only two postlacrymal infraorbital pores and five dentary pores, plus a broad lateral band that widens to at least two and a half scale rows toward the tail and carries into the caudal fin with no caudal spot. Mike Wise, the Apistogramma authority behind the Cichlid Room Companion account, places it in the trifasciata lineage rather than the regani or commbrae groups; the finnage, polychromatism and pore counts are all trifasciata-group hallmarks.
The fish reached the German aquarium trade in 1995 and circulated for years as Apistogramma sp. "Mamoré." It was, and sometimes still is, sold as Apistogramma maciliensis (or "macilliensis"), after Haseman's 1911 Heterogramma trifasciatum maciliense — a name now treated as a synonym of Apistogramma trifasciata, and one Wise argues cannot be reliably tied to the Mamoré fish at all. On a price list, "Apistogramma maciliensis" is most likely a mislabelled erythrura.
Morphology
Apistogramma erythrura is a small, fairly deep-bodied dwarf cichlid, its body depth 34–38% of standard length. Males grow to about 1.7 in (1.5 in SL) and outsize the plainer females. They also carry the showy finnage of the trifasciata group: greatly elongated front dorsal-fin lappets — the third to fifth spines longest — and thread-like pelvic filaments that can reach back to the end of the anal-fin base.
The tail is the signature. It is rounded, and in most adult males flushes partly or wholly bright red, sometimes veiled by a faint reticulation of dark vertical spot-stripes. A broad, sharp-edged lateral band runs from the head, widening toward the tail, and continues into the front half of the caudal fin without breaking into a caudal spot.
What really sets the species apart is its polychromatism: one wild population produces several male morphs side by side. Staeck and Schindler recorded blue versus yellow body grounds, red versus clear (hyaline) tails, and white versus yellow heads all varying independently, so a single brood can throw many colour combinations. The inner iris is bright red in every morph. Females are more uniformly yellowish, deepening to lemon-yellow with a black preopercular spot and dark leading edges to the dorsal and pelvic fins when they brood. Dimorphism is therefore strong — males are bigger, longer-finned and usually red-tailed — but it is also a trap: a clear-tailed male reads easily as a female, which is why sexing this fish by tail colour alone, handy as the shortcut is, can leave an unlucky buyer with two males sold as a "pair."
Habitat
Apistogramma erythrura is a lowland Amazon fish of northern Bolivia. Its confirmed sites lie in the drainage of the lower río Mamoré in Beni department, reaching from the río Yata in the west — the Laguna Larga type locality and lagoons near Santa Ana de Yacuma — east to the río Itonamas drainage at Laguna Mapawa, north of Magdalena. Aquarium material has also come from the neighbouring Guaporé basin and from Lago das Cobras in the río Pacaás Novos system across the border in Rondônia, Brazil, so although the documented core is Bolivian, the fish spans several upper Madeira tributaries.
These are clear-water habitats, not the tea-stained blackwater many keepers assume for a dwarf cichlid. Staeck and Schindler recorded transparent, colourless water that is acidic and very soft: pH 5.2–6.4, conductivity under 10–20 µS/cm, total and temporary hardness below 1 °dH, and notably warm temperatures of 77–88 °F (77–88 °F). The fish stay in dense bankside vegetation, most abundant in floating meadows of water hyacinth (Eichhornia azurea) laced with floating Paspalum repens grass, Cabomba furcata and bladderwort (Utricularia), and were also netted in flooded terrestrial grass and leaf litter in extremely shallow water. They favour standing or barely moving water. Startled in the meadow, they will leap clear and lie motionless on emersed leaves for ten or twenty seconds — an odd but effective way to shake a predator. The same preferences carry into the aquarium: the fish settle best over fine sand under dim light, with floating plants and heavy cover standing in for the meadow, and they want clean, very soft, slightly acidic water rather than true blackwater.
Feeding
Apistogramma erythrura is a micro-predator of the leaf litter and root tangle, with an estimated trophic level around 3.3. Stomach contents of wild fish in the original description were dominated by small locally produced invertebrates: anomopod cladocerans (water fleas) led the list, with a few copepods and other tiny prey. That matches the genus's habit of picking small crustaceans, insect larvae and other meiofauna off sediment and plant surfaces. Sand-sifting and substrate-combing are core to how it feeds, which is why keepers offer fine silica sand rather than gravel — it lets the fish sift as they do in the wild. By dwarf-cichlid standards it is not fussy; longtime keepers find it takes prepared dry foods readily instead of holding out for live or frozen.
In its floating-meadow community the fish shares the water with a characin-rich fauna — Moenkhausia, several Hyphessobrycon tetras and other small species moving above and through the plant carpet — and at syntopic sites in Brazil it turns up alongside Apistogramma cf. staecki and Apistogramma cf. resticulosa. Small, abundant and fast-breeding, it works both ways in these shallow, productive lagoons: a consumer of micro-invertebrates, and itself food — as adults and fry — for larger predators.
Mating
Aquarium observations by the describers show Apistogramma erythrura to be a polygynous, harem-forming dwarf cichlid — the classic Apistogramma arrangement. A male holds a larger territory containing several potential spawning caves; inside it, individual females take smaller sub-territories, each built around a cave. Experienced breeders describe the same structure, calling the species "very polygamous," with several females spawning under one male, though a simple pair will spawn readily too. As in other trifasciata-group fish, a territory-holding male can be fairly aggressive, and a female guarding a brood becomes decidedly pugnacious.
Because the male defends a sizeable area, space and broken sightlines matter for getting pairs or harems to settle and court. Keepers give a pair a generous footprint and more for a harem, and set out multiple caves or coconut and clay breeding huts so each female can claim and court at her own site. Newly imported or freshly paired fish are often genuinely shy and slow to start, and crowding the bottom with competitors backfires — adding corydoras to a breeding setup is a common mistake that just distracts and stresses the apistos.
Breeding
Apistogramma erythrura is a secretive, female-tending cave spawner. The female lays and fertilizes her clutch on the ceiling or wall of a dark cavity — a rock crevice, a hollow, or in the tank an inverted pot or breeding hut — then does the close work herself, guarding eggs and wrigglers inside the cave and later leading the free-swimming fry through cover, while the male patrols and defends the wider territory. Broods are modest: one breeder reports females often raising only 20–30 free-swimming fry per spawn.
Like most dwarf cichlids it is nudged toward spawning by soft, acidic, warm water, but it does not demand extreme blackwater to breed — it comes from clear water and spawns in clean, soft, slightly acidic conditions. Keepers report healthy fish and successful spawns around pH 6.3–6.4 with TDS of 70–80 ppm, close to the very soft wild chemistry, and stress that the fish needs clean, good-quality water to hold condition. By dwarf-cichlid standards it rates about as easy to keep and breed as Apistogramma trifasciata.
In the aquarium
Apistogramma erythrura is uncommon in the hobby — it surfaces in specialist shops and at dwarf-cichlid auctions, usually as erythrura or under the mislabel "Apistogramma maciliensis," and rarely in front of a beginner. Keepers rate it an intermediate-difficulty Apistogramma: easier than the demanding blackwater species, not as bulletproof as staples like Apistogramma cacatuoides. Its water chemistry and its sensitivity to organic waste drive that middle rating.
Water: wild fish come from clear, extremely soft, slightly acidic standing water — conductivity below 20 µS/cm, pH 5.2–6.4, hardness near zero, 77–88 °F (77–88 °F) — and the tank has to match it for the fish to thrive long term. The standard route is reverse-osmosis water reconstituted to 50–100 µS/cm (about 70–80 ppm TDS) with a commercial mineral supplement, which brings pH into range on its own. These are not blackwater fish, so peat or Indian almond leaves alone will not "make it acidic" if the base water is hard; clean, chemically soft water and filtration against ammonia and nitrate matter more than any amber tint.
Tank and decor: give a harem of one male and two or three females an 31.5 in footprint or longer (roughly 20–25 US gal; a 20-gallon "long" is the well-cited minimum for a single pair). Use fine silica sand, not gravel, which blunts sand-sifting and can scrape mouths. Cover is essential — floating plants (frogbit, Amazon frogbit, or water lettuce in a warm tank) over Java fern, Cryptocoryne or fine-leaved stems — plus one cave per female (terracotta pots on their sides, notched coconut halves, or ceramic breeding huts), spaced so each female can hold her own corner without constant chasing. A scatter of dried catappa or oak leaves feeds the infusoria and tiny invertebrates that first-feeding fry graze.
Tankmates: pick small, active upper-water dithers that stay off the bottom — the Hyphessobrycon and Moenkhausia tetras of the same Mamoré and upper-Madeira waters suit both ecologically and in practice. Avoid other bottom-dwellers while breeding; corydoras in particular tip brooding females into aggression or abandonment just by patrolling past them.
Buying a pair: the "red tail means male" shortcut is unreliable here, since clear-tailed males exist. Look instead for a male's elongated dorsal lappets, longer pelvic filaments and greater size; a female stays smaller and shorter-finned, and in spawning condition turns lemon-yellow with a black preopercular spot — the clearest mark in the tank. The usual mistakes to avoid: too small a tank for a pair, untreated hard tap water, too many bottom-competitors in a breeding tank, and reading a clear-tailed young male as a second female.
Conservation
The IUCN Red List assesses Apistogramma erythrura as Least Concern — assessed on 28 October 2020 by R. G. Frederico and published in the 2025 release — with no CITES or CMS listing. For honesty, the species was still "not evaluated" when the Cichlid Room Companion profile was written in 2008, so older accounts predate the current status. As a small, fast-maturing fish with high biological resilience and low fishing vulnerability, it is not under collapse-level pressure, and collection for the ornamental trade is real but modest and localized — exported in limited numbers, and uncommon in the hobby rather than mass-harvested.
Least Concern, though, is not the same as untouched. Apistogramma erythrura is a habitat specialist of shallow floating-meadow lagoons in the lower Mamoré, and the wider Amazon and Madeira lowlands face mounting pressure from deforestation, agricultural expansion and cattle ranching — and, most pointedly for the upper Madeira system it lives in, large hydropower dams (Santo Antônio and Jirau on the Madeira) that reshape flow, sediment and the seasonal flood pulse the floating meadows depend on. The Neotropical cichlid fauna of these basins is documented in Kullander's family treatment in the Check List of the Freshwater Fishes of South and Central America (2003) and in the long line of Amazon fish-community ecology following Lowe-McConnell — work that frames the regional worry as habitat change rather than direct over-exploitation of any single small cichlid. In short, the species itself is secure and breeds freely, but the clear-water lagoons it needs are exposed to land-use change and altered river hydrology across the basin — a watch-the-habitat case, not a watch-the-species one.