Taxonomy & naming
The Swedish ichthyologist Sven O. Kullander described Apistogramma luelingi in 1976, in the journal Bonner Zoologische Beiträge, working from material that Karl-Heinz Lüling and Arnim Meyer had collected on Lüling's 1966 Peru-Bolivia expedition. Those specimens arrived with a tangled history. Hermann Meinken had first filed them as the superficially similar Apistogramma borellii, and only on re-examination did Kullander recognise an undescribed species. The name he gave it is the combination still in use. The holotype sits at the Zoologisches Forschungsmuseum Alexander Koenig in Bonn (ZFMK 2283), alongside a paratype series (ZFMK 2284–2291 and 2303). The type locality carries a wrinkle worth flagging: the 1976 description placed it on the Río Chapare near Todos Santos, but Kullander corrected that in his 1986 monograph on the cichlids of the Peruvian Amazon to a quebrada — a ravine — with backwater below San Francisco, beside the Río Chiripiri in Bolivia, part of the upper Mamoré system. Within the genus, Apistogramma luelingi belongs to the regani species-group: the relatively plain, southern-distribution Apistogramma whose lateral band lacks a distinct mid-flank spot. Aquarists sometimes lump it loosely with the cacatuoides-complex on the strength of surface pattern, but the formal placement follows Kullander. The genus name Apistogramma (Regan, 1913) joins the Greek apistos, 'inconstant' or 'uncertain', to gramme, 'line' — a nod to the variably developed, often interrupted lateral line that runs through the group. The species epithet honours the collector, Lüling himself.
Morphology
Even among dwarf cichlids, this is a small fish. FishBase gives a maximum of about 1.5 in standard length — snout to tail base — for males and roughly 1 in for females; add the tail and a large male still measures only around 1.5–2 in. The body is moderately elongate rather than deep: Kullander put body depth at about a third of standard length and head length at much the same, on a bluntly pointed snout with a notably wide interorbital. Fin counts run to fifteen or sixteen dorsal spines with five or six soft rays, and three to four anal spines, usually four. The colour is understated — a brownish to greyish ground crossed by a dark longitudinal lateral band, with two (sometimes three) rows of dark spots along the abdominal flank and no midventral stripe in a resting fish. The lateral line is rudimentary, exactly as the genus name advertises. Sexual dimorphism sharpens with size. Males grow larger and, past about 1 in, begin to extend the soft dorsal and caudal fins and to flush a metallic blue and yellow across the head and flanks; ripe females turn a vivid yellow and show the black submarginal pelvic-fin edge and the dark suborbital and midventral stripes typical of a brooding female Apistogramma. In smaller, immature fish the sexes are hard to tell apart without a close look at finnage and pigment.
Habitat
Apistogramma luelingi lives on the upper Amazon's southwestern fringe. The Catalog of Fishes summarises its range as the Madre de Dios and Mamoré basins within the greater Amazon basin, across Bolivia and Peru; the IUCN assessment adds the Beni basin in Bolivia and records from the lower Nanay and the Napo–Algodón region of northeastern Peru. Like most of the genus it stays in the shallows — the littoral margins of lakes, small streams, and seasonally flooded ground under vegetation cover. No in-situ chemistry has been published from the type locality itself, but collectors have measured the wider Mamoré-system biotope it shares with congeners such as Apistogramma linkei and Apistogramma staecki: water often just 1–3 ft deep, threaded with dead leaves, submerged wood, and the roots of floating plants like Eichhornia and Pistia, and soft, warm and acidic — pH around 5.7 to 6.6, conductivity in the low tens of microsiemens, hardness under 1 °dH, and field temperatures near 84 °F. FishBase lists a narrower preferred band of about 72–79 °F for the species. Here it shares the water with other small cichlids — Aequidens dorsiger, Crenicichla lepidota, and Cichlasoma boliviense among them — a community of shallow, vegetated backwaters rather than the open river channel.
Feeding
No dedicated diet study exists for Apistogramma luelingi, and FishBase's trophic level of about 3.2 is estimated from its close relatives rather than measured from gut contents. The ecology is best read from the genus. Apistogramma are micro-predators of the leaf litter and shallow substrate, grazing biofilm and sifting fine sediment for small benthic invertebrates — chironomid and other insect larvae, microcrustaceans, worms, and the organic detritus that comes with them. Small, subconical, slightly recurved jaw teeth and a modest gape suit a fish that picks and winnows at the bottom rather than one that chases larger prey. In the aquarium it takes small live and frozen foods readily — microworm, baby brine shrimp, daphnia, cyclops, and fine frozen bloodworm — and keepers agree that conditioning on live food is what brings females into spawning condition. In its own community it is one of the small benthic invertivores of the vegetated margin, and prey in turn for the larger Crenicichla and Aequidens that share the water.
Mating
Socially, Apistogramma luelingi runs the polygamous, female-centred system common to cave-spawning Apistogramma. A dominant male holds a comparatively large territory and tolerates — indeed seeks out — several females inside it, each guarding her own smaller patch around a cave. This is the root of a behaviour that catches new keepers out: a male housed with a single, non-receptive female will drive and harass her without let-up, not from plain aggression but because, in his terms, a territory holding only one un-ready female is a territory that needs more of them. The experienced remedy is space and numbers — give the male room and at least two or three females spread across distinct, broken-up territories with dense cover, so his attention is split and each female can hold her own corner. When a female ripens she colours bright yellow, puts on the dark-marked breeding dress, and courts the male toward her chosen cave. Pair formation is brief and the bond loose: the male's job is to patrol and defend the wider area, not to share the parental work.
Breeding
Apistogramma luelingi is a cave, or concealment, spawner. The female fastens her eggs to the ceiling or upper wall of a small cavity — in the aquarium a half-buried flowerpot, coconut shell, or similar dark chamber — and she alone tends them, fanning the clutch and then guarding and herding the wrigglers and free-swimming fry while the male defends the surrounding territory and, usually, other brooding females within it. Clutch size has not been reported for this species; closely related, similarly sized Mamoré congeners studied by Koslowski lay roughly 50 to 100 eggs per spawning, a reasonable expectation here. In those relatives, at about 75 °F the eggs hatch in around three days and the fry swim free some six days later — a useful guide for Apistogramma luelingi, given how little is published on its own development. The trigger in captivity is chemistry: keepers report success only in soft, acidic water, with documented breedings around pH 6.4 and effectively zero hardness, paired with warmth and a live-food diet. Hard or alkaline water reliably blocks spawning even when the adults are otherwise healthy.
In the aquarium
Apistogramma luelingi is genuinely rare in the hobby — turning up now and then from specialist Apistogramma breeders and at ACA-affiliated auctions, but not at the average store, and seldom exported in quantity. Less is on record than for workhorses like Apistogramma cacatuoides or Apistogramma agassizii, so keepers lean on broader regani-group husbandry and their own notes. It is not difficult as Apistogramma go, only unforgiving of the one thing the genus cares about most: water chemistry.
Tank: 15–20 US gal (about a 60 × 15.5 in footprint) holds one male with two or three females; 25–30 US gal allows more cover, which matters as much as floor space. Use fine, smooth-grade sand and break the floor up generously with leaf litter (Indian almond or oak, replaced as it decays), driftwood and bogwood, and a few flat stones. Caves are non-negotiable for breeding — buried half-coconut shells, ceramic caves, or small clay flowerpots on their side, at least one per female plus a spare — and low-light plants like Microsorum, Anubias and small Echinodorus, with floating cover to soften the light, finish a layout the fish will actually use.
Water: the commonest failure here. This is a soft-water, acidic specialist from a system running in the low tens of microsiemens with pH below 6.5; the Mamoré field data give pH 5.7–6.6, and successful breedings come only around pH 6.4 or lower with hardness near zero. Tap water above about 6 °dH and pH 7.0 keeps adults alive but suppresses breeding and stresses them; lightly remineralised reverse-osmosis water, or an RO-and-soft-tap blend, is the practical fix. Hold 72–79 °F — the low end for maintenance, the high end to prompt spawning — and keep filtration gentle with a sponge filter or a spray bar against the glass, since this is a still-backwater fish, not a current-lover.
Tankmates: small and peaceful only. Surface characins make good dithers — Hyphessobrycon species, small Moenkhausia, ember tetras — working a different layer and ignoring fry; Corydoras or small Otocinclus share the bottom without competing. Avoid anything large enough to eat fry or bold enough to contest caves, and keep other cichlids out altogether, as even peaceable Apistogramma unsettle the territory structure. Favour a harem of two or three females over a lone pair, spreading the male's attention as the Mating section explains.
Common mistakes: hard or alkaline water first, then pairing a single female with the male. Sexing is easy from sub-adult size (see Morphology); juveniles need a closer look. Because the species is offered so seldom, anyone who lands it and gets the chemistry right does real good by breeding it — documented captive records are sparse, and careful notes add genuinely to what is known.
Conservation
The IUCN Red List assesses Apistogramma luelingi as Least Concern — assessed on 25 April 2014, published in 2016 by Correa, Maldonado, Carvajal and Sarmiento — on the grounds that it is widely distributed across the Madre de Dios, Beni and Mamoré basins, occurs inside protected areas (it is recorded from Bolivia's Tambopata-Candamo National Park and near Peru's Allpahuayo-Mishana National Reserve), and faces no major widespread threats. The assessment is flagged as needing an update, the population trend is listed as unknown, and the species is called uncommon in at least one surveyed area — the Maijuna territory of northeastern Peru. It is collected for the ornamental trade and exported from Peru, but at a level the assessors do not treat as a population-level risk; the only specific pressures they note are local, chiefly habitat modification and pollution from livestock farming. There is no CITES listing. As a small specialist of shallow, vegetated margins, its longer-term exposure is less to the dam-and-channel pressures that weigh on big river fish than to the erosion of those backwaters — cleared marginal vegetation, siltation, and agricultural runoff — across a still under-collected corner of the southwestern Amazon.