Taxonomy & naming
Apistogramma rubrolineata was described in 2002 by Gerd Hein, Axel Zarske and Jaime Zapata, in the German aquarium-hobby journal Das Aquarium (issue no. 402, pages 15-19), on fish collected from the Rio Manuripi in the lowland northwest of Bolivia. The type locality is precise: a stretch of the Manuripi near the settlement of Puerto Cardenas, at 11 degrees 20.083' S, 67 degrees 44.576' W, in the Departamento Pando. The holotype is held at the natural-history collections in Dresden (Museum fuer Tierkunde Dresden, register MTD F 26477), with paratypes distributed among the Dresden, Vienna (NMW), Bonn (ZFMK) and Bolivian (CIRA-UTB) collections. (A note on the basin label sometimes attached to this fish: the Manuripi is not part of the Mamore system but of the Madre de Dios drainage, which joins the Beni and then the Madeira - so while 'upper Madeira basin' is correct at the coarse scale, the specific home water is the Manuripi-Madre de Dios, not the Mamore.) Eschmeyer's Catalog of Fishes lists the species as valid with no synonyms, an uncomplicated nomenclatural history for a genus where misidentification is the norm. Within Apistogramma - a genus of well over a hundred described species and several hundred known forms - rubrolineata belongs to the regani lineage, and is placed by the specialist Mike Wise in the resticulosa species-complex of the regani group. That placement matters in practice: imported fish are routinely confused with Apistogramma resticulosa and with an undescribed 'Apistogramma cf. resticulosa Madre de Dios', and shipments labelled rubrolineata frequently arrive mixed with eunotus-complex and commbrae-complex look-alikes. The genus name, coined by Charles Tate Regan in 1913 as a replacement for the preoccupied Heterogramma, joins the Greek apistos ('uncertain', 'inconstant') to gramme ('line') - an allusion to the genus's variably developed, often interrupted lateral line. The epithet is plainer: Latin rubrus, red, and lineatus, lined, 'red-lined', for the seven dark-red stripes the describers used to diagnose it.
Morphology
This is a small fish even by dwarf-cichlid standards. FishBase gives a maximum of about 1.5 in standard length (snout to tail base); in keepers' terms a good wild male reaches roughly three inches including the tail, and females stay around two. The body is fusiform and only moderately compressed - a workmanlike shape rather than the high-finned drama of cacatuoides or the macmasteri group. Fin counts run to fifteen or sixteen dorsal spines with seven or eight soft rays, and three anal spines with six or seven soft rays. The ground colour of a male is a light olive, crossed by a dark, slightly zig-zagging lateral band that ends in a spot on the caudal peduncle; the face and the rays of the dorsal, ventral and anal fins carry a metallic green, sometimes warmed with yellow. The diagnostic feature - the one the name advertises - is a set of seven fine brown-red lines running the length of the flanks along the rows of scales, above and below the lateral band, together with a characteristic arc where the postorbital stripe meets the midlateral band. Importantly, those red lines are a mood signal: collectors and importers note that they show in full only on dominant, displaying males, and a fish at rest can look almost unmarked, which is part of why the species is easy to overlook in a dealer's tank. Sexual dimorphism follows the usual Apistogramma pattern - males grow larger, longer-finned and more colourful; females are a drab grey-brown most of the time but turn an intense lemon yellow with bold black markings when guarding eggs or fry.
Habitat
Apistogramma rubrolineata is a fish of the upper Amazon's far southwestern fringe, the Madre de Dios river system that drains the Andean foothills of southeastern Peru and northern Bolivia. The IUCN summarizes its range as the Madre de Dios basin in both countries, known from only about three sites - the Manuripi type locality in Bolivia's Pando department and localities within the Tambopata region of Peru - at elevations between roughly 140 and 200 metres. The original description characterizes the type habitat as a typical black-water river with loamy banks, and the IUCN adds that it lives in slow-flowing streams. The most useful in-situ data come from collectors rather than the literature: an October-2017 collecting party that took the fish from a clear, shallow forest creek in Peru's Madre de Dios recorded soft, clear water of about 17 ppm total dissolved solids, pH 6.5 and roughly 24 degrees C (75 degrees F), over a mixed mud-and-gravel bottom, in water mostly knee-deep with a few deeper holes - very little aquatic vegetation, but bankside forest plants trailing into the margins. FishBase's preferred ranges (a lower pH limit near 5.9, a temperature band around 22-28 degrees C typical of the genus) are consistent with that picture. In short, this is a shallow, warm, soft-and-acidic blackwater fish of small forest streams, sharing its water with tetras and several Corydoras, exactly the leaf-litter-margin community the genus is built for.
Feeding
No dedicated diet study has been published for Apistogramma rubrolineata, and FishBase's trophic level near 3.3 is an estimate derived from its relatives rather than from gut contents. Its ecology is read from the genus: Apistogramma are micro-predators of the shallow substrate and leaf litter, picking biofilm and sifting fine sediment for small benthic invertebrates - chironomid and other insect larvae, microcrustaceans, worms and the associated organic detritus. The small mouth and modest dentition fit a fish that winnows and picks at the bottom rather than one that chases larger prey. In the aquarium it is undemanding and accepts a wide menu: keepers report wild-caught fish taking flake from the start and thriving on a rotation of live and frozen foods - blackworm, whiteworm, daphnia, mosquito larvae, chopped earthworm and frozen bloodworm - with newly hatched brine shrimp the standard first food for fry. In its forest-stream community it is one of the small benthic invertivores of the vegetated margin, and prey in turn for the larger fish that share the same shallow water.
Mating
Socially, Apistogramma rubrolineata runs the female-centred, loosely polygamous system that characterizes most cave-spawning Apistogramma, but with a notably mild temper for the genus. Keepers who have kept groups describe it as far less aggressive than many congeners: males spar with flared fins and chase, but the altercations stay minor, and a single male will hold court over several females without the relentless harassment that drives more pugnacious species. The trigger for spawning is the female's condition rather than elaborate courtship - as she ripens she colours up bright yellow, claims a cavity, and from then on defends it ferociously against all comers while the male patrols the surrounding territory at a respectful distance. As with the genus generally, a colourless, non-receptive female can become a target for male attention, so the standard advice of giving a male two or more females and plenty of broken sightlines applies, even though this is one of the species where a simple pair is more likely to coexist peacefully than in, say, the macmasteri or trifasciata groups.
Breeding
Apistogramma rubrolineata is a cave (concealment) spawner with the maternal, female-tended care typical of the genus: the female deposits her eggs on the ceiling or wall of a small dark cavity - a half-buried flowerpot, a coconut shell, a hollow under wood - and it is she alone who tends them, fanning the clutch and then guarding and herding the wrigglers and free-swimming fry, while the male defends the wider area. Clutch size has not been formally reported for the species. The most concrete captive record, from a wild-caught group bred in soft, acidic water (around pH 6, 60 ppm TDS, about 27 degrees C), describes a female emerging from her pot leading a brood of roughly forty fry - a modest number consistent with the small body size, and a useful real-world figure in the absence of a published fecundity count. The fry took newly hatched brine shrimp immediately and grew quickly, reaching about three-eighths of an inch by three weeks and nearly three-quarters by six, beginning to spar like miniature adults soon after; the parents largely ignored the juveniles once they stopped following the mother. The consistent message from keepers is that this fish breeds readily and is undemanding by Apistogramma standards, provided the water is soft and acidic - the same blackwater chemistry that defines its native streams.
In the aquarium
Apistogramma rubrolineata is rarely seen in the trade. It appears sporadically in specialist importations from Peru, nearly always as a by-catch in mixed Apistogramma consignments rather than as a targeted collection, and availability outside Europe and North America is essentially nil. Keepers who have obtained it consistently describe it as one of the genus's more tractable species - less aggressive than many of its relatives, easier to manage as a group, and willing to breed in captivity provided the water chemistry is right. That last qualifier is non-negotiable: this is a soft, acidic blackwater fish from shallow forest streams, and attempts to keep it in the moderately hard, neutral water that suits cichlids from the Rift Valley or even the harder Amazon systems will produce a stressed, pale, short-lived fish. Target water in the pH 6.0-6.5 range, with total dissolved solids below about 50 ppm, and temperature between 24 and 27 degrees C; the in-situ Peru collection that documented a spawning was run at roughly those parameters (pH 6.5, ~17 ppm TDS, ~24 C), and a slightly warmer, softer setup around pH 6.0-6.2 with blackwater extract added is a reasonable aquarium target for conditioning and spawning. Avoid the common mistake of treating generic 'soft-water' conditions as interchangeable - this species evolved in water considerably softer and more acidic than, say, the tap water of most European or North American cities, and buffering a municipal supply down to pH 6.5 without also reducing total hardness does not replicate the chemistry it needs.
A tank of 15–20 US gal is adequate for a single pair or a harem of one male with two or three females, provided the footprint is broad enough to establish separate female territories - a long, shallow tank is preferable to a deep one. Fine sand substrate is essential: these fish sift and dig constantly, and coarse gravel is both uncomfortable and harmful to the whisker-like ventral fin rays. Leaf litter - Indian almond leaves, oak leaves, beech leaves - is strongly recommended; it acidifies the water gently as it decomposes, provides the dense microhabitat structure these fish use in the wild, and gives females the visual breaks they need to establish distinct territories. Supplement with driftwood, coconut-shell halves (the standard spawning cave), small terracotta flowerpots laid on their sides, and clumps of fine-leaved plants like java moss or Taxiphyllum species along the margins. Aquatic plants are not essential to replicate the natural habitat, which is largely unvegetated, but they help establish the broken sightlines that reduce male harassment of non-receptive females.
The mildness of this species makes tankmate selection more forgiving than with many Apistogramma. Small, peaceful tetras from similar soft-water environments - pencilfish (Nannostomus), small Hyphessobrycon, or Moenkhausia species - serve as ideal dither fish, giving the cichlids a sense of security and distributing male attention. Corydoras from the Madre de Dios system are ecologically authentic companions and practical ones: they occupy the same bottom layer without competing for caves and signal environmental safety to the Apistogramma. Avoid any tankmate large enough to eat the fry once spawning begins, and avoid fin-nippers. Other Apistogramma in the same tank is not advisable unless the aquarium is large enough to partition into separate territories; even this mild species will defend breeding territory aggressively.
Sexing adults is straightforward by standard Apistogramma criteria: males are visibly larger, carry extended dorsal fin rays (the first few spines are prolonged), and display the seven brown-red lateral stripes in full when excited, a pattern that disappears in a fish at rest or under stress. Females are smaller, rounder-bodied when ripe, and lack the stripe pattern except for the suborbital stripe common to both sexes; when guarding eggs or fry they turn a vivid lemon yellow with jet-black mask and fin markings, a transformation that in practice identifies the breeding female before you find the cave. Juveniles are difficult to sex until roughly three months of age, when size differences and fin-ray elongation begin to diverge. The common keeper mistake with this species is acquiring only a single pair and then blaming aggression when the male harasses the female between spawning cycles; giving the male two females to distribute his attention and providing enough structure so each female can hold a discrete hiding spot largely eliminates this problem, even though the species is gentler than most.
Conservation
The IUCN Red List assesses Apistogramma rubrolineata as Data Deficient (assessed 25 April 2014, published 2016, by Correa and Sarmiento), on the explicit grounds that there are no data on its population size, exact distribution or threats. It is known from only about three localities in the Madre de Dios basin of Peru and Bolivia, two of which fall within protected areas - the Tambopata reserve in Peru and the Manuripi-Heath national reserve in Bolivia - so an estimated 21 to 30 percent of its range is nominally protected. The species is collected for the ornamental aquarium trade and exported from Peru, but at a level the assessors did not treat as a documented threat, and it carries no CITES listing. The honest summary is that nobody yet knows how secure it is: a small fish with a tiny known range and a genuinely uncertain status. That narrowness is the heart of the matter. Unlike the genus's wide-ranging species, a fish confined to a handful of shallow forest streams in one corner of the basin is exposed precisely to the local pressures that bear hardest on such habitats - deforestation and the clearing of streamside vegetation, siltation, and the dam-building and gold-mining that increasingly reach the headwater drainages of the southwestern Amazon. None of these is documented as a present danger to this particular cichlid, but for a Data Deficient, narrow-range endemic they are the backdrop against which any future assessment will be read.