Taxonomy & naming
Apistogramma martini was described in 2003 by Uwe Römer, Ingo Hahn, Eva Römer, David P. Soares and Martin Wöhler, in the German aquarium journal Das Aquarium (issue 37(4), No. 406, pages 14–29), under the title "Apistogramma martini sp. n. – Beschreibung eines geophaginen Zwergcichliden." It rests on a large type series of 69 specimens: the holotype and much of the material sit at the California Academy of Sciences as CAS 225481, with a paratype lot of ten (ZFMK 39412–39421) in the Zoologisches Forschungsmuseum Alexander Koenig in Bonn. The type locality is a small tributary of the Río Nanay near the settlement of Alvarenga — formerly Puerto Alianza — in the Santa María District, Maynas Province, Loreto Department, northern Peru, at roughly 03°31'10"S, 74°25'40"W and about 361 ft elevation.
The genus name pairs Greek apistos, "uncertain" or "inconstant," with gramma, a written mark or line — a nod to the variable, often incomplete lateral-line markings that made these dwarfs so hard for early workers to pin down (FishBase glosses the second root as "graphic signal," the same idea). The epithet honours Martin Mortenthaler (1961–2018), who ran the ornamental-fish exporter Rio Momon EIRL — formerly Aquarium Rio Momon — in Iquitos and supplied the type material; the dwarf pencilfish Nannostomus mortenthaleri carries his name too.
Where the fish belongs inside Apistogramma — the richest of all Neotropical cichlid lineages, with ninety-plus valid species and many undescribed forms — is genuinely unsettled. The original description and FishBase place it in the cacatuoides complex, the diagnosis calling it "a representative of the Apistogramma-cacatuoides-complex"; the Cichlid Room Companion instead lists it in the Nijsseni group. The two schemes have never been reconciled, and a squat, sexually dichromatic dwarf like this one sits awkwardly between them, since Apistogramma group concepts lean on subtle, mood- and maturity-dependent detail. The describers separate it from every other Apistogramma by one combination of characters: a lyre-shaped caudal fin in both sexes, a low dorsal fin edged top and bottom by two coloured bands, a dark blotch at the base of the soft dorsal rays, a large spot on the caudal peduncle, and a distinct lateral spot that is enlarged in females.
Morphology
This is a genuinely tiny fish. FishBase gives a maximum of about 1 in standard length, so even a well-grown male is barely an inch in the body, with the fins adding a little more. The sexes diverge sharply, as in most Apistogramma. Males are the larger, more elongate sex, washed blue-grey with yellow about the head and the unpaired fins and carrying the species' lyrate, two-banded caudal fin. Females are smaller, and in brooding dress they turn an intense golden yellow scored with bold black — the enlarged flank spot, dark pelvic fins and facial marks that are the visual language of a guarding Apistogramma mother.
Separating Apistogramma martini from its near-twins is a matter of fine detail rather than one obvious field mark. The describers rely on the shape of the lyrate caudal and its paired bands, the dark spot at the base of the soft dorsal rays, the size and position of the caudal-peduncle spot, and the enlarged female lateral spot. All of these shift with mood, water chemistry and maturity, which is exactly why dwarfs of this kind have a long history of mislabelled imports. A single photograph is a weak basis for an identification here; the diagnosis rests on the describing paper's morphometrics, not on colour. Tellingly, no image of a verified specimen even appears on the FishBase page — a measure of how little photographed and little traded the species remains.
Habitat
Apistogramma martini is a Peruvian Amazon endemic, known essentially from the Río Nanay drainage in Loreto, in the lowland forests around Iquitos. Its IUCN assessment describes a restricted range centred on the type locality — a small Nanay tributary near Alvarenga — and FishBase records it simply as "South America: Peru." GBIF holds only a small scatter of records (around 84), which fits a narrowly known, infrequently collected fish.
The habitat is classic western-Amazon dwarf-cichlid country: small, shaded forest brooks — locally quebradas — with sandy bottoms, leaf litter and submerged wood, draining the nutrient-poor white-sand forests as slow, tannin-stained blackwater that is very soft and acidic. At the type locality Apistogramma martini lives side by side with the dwarf pencilfish Nannostomus mortenthaleri, another Nanay blackwater specialist, in small sandy creeks. Field work on the region's Apistogramma habitats (Beninde, Römer and colleagues, 2020) shows how the forest canopy governs these waters: shaded creeks stay cooler and better oxygenated, while measured temperatures across inhabited sites ran from about 76–96 °F, mean near 82 °F, with the hottest readings where deforestation had opened the canopy. The in-situ chemistry the describers reproduced for healthy maintenance — very soft water near 100 µS/cm, pH about 6 to 6.5, over fine silicate sand with beech-leaf litter — is a fair proxy for the wild brook. This is a leaf-litter specialist's world, dim and tea-dark, not an open-river one.
Feeding
No dedicated field study of this fish's diet has been published, so its ecology is read from its anatomy, its close relatives and the general biology of leaf-litter Apistogramma — and that inference is consistent and well grounded. FishBase puts it at a trophic level near 3.2, squarely in the micro-carnivore range. Like other litter-dwelling dwarf cichlids, it is best understood as a micropredator that sifts and picks through detritus, leaf litter and the surface of the sand for small invertebrates: aquatic insect larvae, microcrustaceans such as copepods and ostracods, worms and other meiofauna. In the tank it takes and conditions well on small live and frozen foods, which fits the same picture.
In a blackwater forest creek a fish this size is both a small predator on invertebrates and potential prey for larger fishes, birds and the odd snake. Its cryptic colour, small defended patch of bottom and habit of staying close to cover all suit a life spent threading the litter rather than crossing open water.
Mating
Courtship observations specific to Apistogramma martini are scarce, and because the fish's group placement is itself contested, it would be a mistake to graft the well-documented harem biology of any one complex straight onto it. What can be said is broad but well supported across the genus. Apistogramma of this body plan are typically harem-polygynous cave spawners: a male holds a larger territory overlapping the smaller territories of one or several females, and the female does the close work of choosing and preparing a spawning cavity. She drives courtship near that cave, signalling readiness in the vivid yellow-and-black brooding dress, while the male's role narrows to fertilisation and perimeter defence. These dynamics are governed by aggression at very small scales, which is why keepers of the complex stress giving each female her own cave and cover. The describers kept the type stock in soft, slightly acid water in small, sexually balanced groups precisely to allow free mate choice — a reminder that reproduction in these dwarfs is driven as much by female preference as by male display.
Breeding
Spawning has not been documented in the wild for Apistogramma martini specifically, but the genus pattern is clear and the species conforms to it. Apistogramma are cave-spawning, substrate-brooding dwarfs in which the female is the primary parent. She lays a clutch on the roof or wall of a small cavity — a crevice, a hollow under wood or litter, or in the tank a half-buried flowerpot or coconut shell — then guards and fans the eggs, leads the wrigglers and free-swimming fry in a tight school, and drives off intruders, the male often among them. A few dozen fry is typical for litter-dwelling dwarfs this small, with clutch size rising as the female matures; congeners in the same Peruvian guild can reach around 200 fry per spawn in large, old females, but a three-centimetre fish will lay far fewer. The reliable trigger for the complex is water chemistry: soft, acidic, tannin-stained water, warmth and a rich, partly live diet. Fry are free-swimming within a few days of hatching and are grown on small live foods such as microworm and newly hatched brine shrimp. As with the husbandry chemistry, these specifics are genus-typical inference — flagged as such — because no spawning report tied to a verified Apistogramma martini has been published.
In the aquarium
Apistogramma martini is rarely encountered in the hobby. It reaches the trade only occasionally, usually as by-catch in other Peruvian dwarf-cichlid shipments through Iquitos exporters, and it is almost never offered under its correct name — most fish sold as nijsseni- or cacatuoides-group dwarfs from the Nanay will be something else. Anyone after it should expect to trace the export chain and should treat any fish labelled Apistogramma martini as a tentative identification unless a Río Nanay origin can be confirmed. Under the right conditions it is not a difficult fish; the difficulty is the chemistry, not the temperament.
Tank: A 15–20 US gal aquarium suits a harem of one male with two or three females, and a single pair will manage in 10–15 US gal, though more room reduces female-on-female aggression and gives subordinates somewhere to hide. Because the fish tops out near 1 in, footprint matters more than volume — a longer, shallower tank beats a tall one. Use fine silicate sand at least 1–1.5 in deep for sifting, and treat dry leaf litter (beech, oak, catappa) as functional rather than decorative: it reproduces the micro-habitat, adds cover, gently acidifies the water as it breaks down, and settles fish that would otherwise hide. Driftwood and roots add structure, and low plants such as Cryptocoryne or a mat of floating vegetation dim the light. Each female needs at least one dedicated spawning cave — a half coconut shell, an upturned clay pot with a small entrance, or a hollow under wood — or harem dynamics turn dangerously competitive.
Water: Chemistry is non-negotiable. The wild type locality is extreme blackwater — very soft (around 100 µS/cm, roughly 2–4 °dGH), pH 6.0–6.5 per the type-stock chemistry, and 75–82 °F for routine keeping, with a short lift to about 84–86 °F as a breeding trigger. Dilute tap water with RO or rainwater; peat filtration and botanicals help soften and stain it. Fish held in harder, more alkaline water survive but rarely breed, colour poorly, and grow more prone to bacterial infections of the fins and skin — a common mistake in a genus notorious for chemistry sensitivity. Keep filtration gentle, a mature sponge filter or a small canister on a spray bar; these are fish of near-still creeks, and strong flow stresses them.
Tankmates: Choose by size and by the same soft-water needs. Pencilfish of the genus Nannostomus are the natural dither — Apistogramma martini shares its wild creek with Nannostomus mortenthaleri, so the pairing is ecologically apt, not just convenient. Small blackwater tetras (Paracheirodon axelrodi in soft RO water, Hyphessobrycon species matched to Peruvian conditions) work in a larger tank, and soft-water Corydoras such as Corydoras sterbai or Corydoras weitzmani make unobtrusive bottom company. Avoid barbs, fin-nippers, large tetras and anything big enough to see a 1 in cichlid as food. Never house two Apistogramma males together, and watch the body condition of subordinate females, since in a small tank a dominant female will steadily exclude and injure them.
Common mistakes: Buying fish sold as martini from an untrusted source, dropping them into untreated tap water, and feeding only dry flake are the reliable routes to failure. Sexing adults is otherwise easy — males are larger and more elongate with a longer dorsal and the lyrate, two-banded caudal, while mature females flush intense yellow-and-black at any sign of spawning. Difficulty is moderate for an experienced soft-water keeper and high for a beginner: not because the fish is fragile in the right water, but because reaching and holding that water takes both equipment and discipline.
Conservation
Apistogramma martini is listed on the IUCN Red List as Least Concern (Ortega Torres 2016; assessed 25 April 2014, published 2016, criteria version 3.1). The assessment notes a restricted distribution but a population presumed stable, with no documented major threats and a stable trend. It is explicitly flagged as needing updating, so that bare "Least Concern" is best read as a low-concern snapshot from the mid-2010s rather than a current guarantee. The fish is noted as potentially useful in the ornamental trade — fitting for a species named after an aquarium exporter — but it occurs in no protected area and has no conservation measures in place.
That status is worth reading against the particular vulnerability of these forest-creek dwarfs. The same workers who described it have argued (Beninde et al. 2020) that deforestation is a real concern for many Peruvian Apistogramma: stripping the canopy raises and destabilises the temperature of the small quebradas they depend on, and because temperature can skew sex ratios in the genus, warming their habitat is a demographic threat, not a trivial one. A narrowly distributed, single-drainage blackwater specialist near a growing city like Iquitos is exposed to exactly these local pressures — deforestation and land-use change in the white-sand forests, sedimentation and pollution of small streams, and the risk of over-collection from a handful of accessible sites. None of this yet rises to a documented, population-level threat for Apistogramma martini. The honest summary is the careful one: a Least Concern species with a small range in a region under genuine but diffuse pressure — not endangered, but worth watching precisely because so little of its wild biology has been studied.