Taxonomy & naming
Poecilia mechthildae was described by Manfred K. Meyer, Volker Etzel and Dieter Bork in 2002, in the journal Zoologische Abhandlungen of the Staatliches Museum für Tierkunde in Dresden, under the original combination Poecilia (Mollienesia) mechthildae. The holotype (MTD F 26473) and a series of paratypes (MTD F 26474–76 and SMF 28889) were collected about 4 mi upstream of the mouth of the Río Acandí, near Acandí in the Chocó department of Colombia. Eschmeyer's Catalog of Fishes treats the name as valid: Poecilia mechthildae Meyer, Etzel & Bork 2002, within the family Poeciliidae, subfamily Poeciliinae.
The species is placed in the subgenus Mollienesia, the short-finned and sailfin mollies, a grouping reaffirmed in the molecular and morphological work of Palacios and colleagues (2016). It has been carried forward as a valid species in subsequent treatments, including Lucinda & Reis (2005), Poeser (2011), Meyer (2015), the Colombian freshwater-fish checklist of DoNascimiento et al. (2017), and Huber (2019). The specific epithet mechthildae is a patronym, a latinised genitive honouring a person named Mechthild; the genus name Poecilia derives from the Greek poikilos, "many-coloured," a reference to the variegated patterning typical of these livebearers.
Morphology
Poecilia mechthildae is a small freshwater poeciliid of the short-finned molly type. As is universal in the genus, it shows the marked sexual dimorphism of the live-bearing toothcarps: males are smaller and bear a gonopodium — an intromittent organ formed from modified anal-fin rays — while females are larger and deeper-bodied. No measured maximum length is recorded on FishBase or in the readily available literature, so a precise adult size cannot be stated here; the data are sparse, and the diagnostic features that separate it from neighbouring mollies are detailed in the figures (1–4) of the original 2002 description rather than in any popular account.
FishBase carries no photograph of the species, only a placeholder drawing, and provides only a Bayesian length–weight relationship (a = 0.00851, b = 3.15 in cm total length) that is a family-shape estimate rather than a real measurement of this fish. In general body plan it conforms to the Mollienesia pattern — a compact, laterally compressed molly without the exaggerated sailfin dorsal of some relatives — but the specifics of its coloration and meristics rest with the type material in Dresden and Frankfurt and are not reproduced in the general databases.
Habitat
The species is known with certainty only from the Río Acandí and its immediate surroundings on the Caribbean (Atlantic) slope of the Chocó department in north-western Colombia, near the Darién gap and the Panamanian border. Eschmeyer's catalog notes its distribution as northern Colombia and possibly southern Panama, making it a narrow-range, poorly documented endemic of this biogeographically rich and politically difficult border region. Its environment is freshwater; FishBase classes it as benthopelagic and tropical.
No measured water-chemistry data for the type locality have been published in the sources reviewed, so temperature, pH and hardness figures for this species are not asserted here. As a lowland Caribbean-slope river fish from a short-finned molly lineage, it can reasonably be expected to occupy warm tropical fresh water, but the precise parameters of the Río Acandí are not on record in the material available, and the wider ecology of the species — flow regime, substrate, associated vegetation and fish community — remains essentially undescribed.
Feeding
There is no species-specific diet study for Poecilia mechthildae in the available sources. FishBase assigns it a modelled trophic level of about 2.6 (±0.3), an estimate derived from its relatives rather than from gut-content analysis; a value in this range is consistent with an omnivore or detritivore that leans herbivorous, which is the typical feeding ecology of the short-finned mollies.
By analogy with other Mollienesia, the species is likely to graze on algae (aufwuchs) and detritus and to take small aquatic invertebrates and insect larvae opportunistically. This is inference from the genus, not a documented observation for P. mechthildae, and should be read as such. Anyone keeping the fish — should wild stock ever reach the hobby — would be on safe ground offering a molly-style diet rich in vegetable and algal matter, but no captive feeding record for this particular species is known.
Mating
Like all members of the genus Poecilia, P. mechthildae is presumed to reproduce by internal fertilisation. The male transfers sperm to the female using the gonopodium, the modified anal fin that is the defining reproductive structure of the poeciliids; courtship and mating in the short-finned mollies generally combine male display with persistent pursuit of females, who can store sperm and produce successive broods from a single insemination.
No species-specific courtship or mate-choice observations exist for P. mechthildae in the reviewed literature — the FishBase reproduction, fecundity and spawning fields are empty for this fish. What is described here is therefore the general poeciliine pattern as it applies to the genus, not behaviour documented in this species. The detail of its mating system, if it differs at all from its molly relatives, has not been studied.
Breeding
Poecilia mechthildae is, on the strength of its genus, a viviparous livebearer: after internal fertilisation the female carries the developing embryos and gives birth to free-swimming young rather than laying eggs. In Poecilia the embryos are essentially lecithotrophic, nourished by their own yolk, with the strong maternal provisioning (matrotrophy) and superfetation seen in some other poeciliids — for instance Heterandria and Poeciliopsis — generally minimal or absent. Superfetation is not expected in this species.
Brood size, gestation length and the timing of maturity have not been documented for P. mechthildae; these fields are blank on FishBase and the figures are not given in the literature reviewed, so the data here are genuinely sparse. FishBase does rate the species' resilience as high, with an estimated population-doubling time of under 15 months, which is consistent with the rapid, repeated reproduction typical of livebearing toothcarps even though no actual brood counts for this fish are on record.
In the aquarium
Poecilia mechthildae is effectively absent from the aquarium hobby. It is not a commercially traded fish, there is no established line in captivity, and no husbandry account specific to the species exists in the sources reviewed — so any care advice can only be extrapolated from the well-known short-finned mollies rather than verified for this fish.
Were wild stock ever to become available, a keeper would most reasonably treat it as a typical Mollienesia molly: warm, stable, well-filtered fresh water; a vegetable-leaning omnivorous diet; and the usual livebearer caveat that adults will eat free-swimming fry, so cover or separation is needed to raise young. None of these points is documented for P. mechthildae specifically, and the honest position is that its captive requirements are unknown. FishBase rates it harmless to humans, with a low fishing-vulnerability score (10/100).
Conservation
The IUCN Red List assesses Poecilia mechthildae as Data Deficient (DD), assessed on 10 October 2014 (species ID 64694003, assessment 64890385). The Data Deficient category reflects exactly the situation outlined in this article: a poorly known, narrowly distributed endemic for which there is not enough information to judge extinction risk. It is not listed under CITES or CMS, and FishBase records its conservation status as not otherwise evaluated.
A Data Deficient listing is not a verdict of safety. A species known from essentially one river on a single Caribbean-slope drainage, in a region under pressure from deforestation and land-use change, could be genuinely at risk without anyone having the survey data to demonstrate it — which is precisely why DD species are flagged as research priorities. For P. mechthildae the most valuable contribution would be basic fieldwork: confirming its range, characterising its habitat, and documenting its biology, all of which remain largely blank.