Taxonomy & naming
Poropanchax stigmatopygus was formally described by Wildekamp and Malumbres in 2004. Because the name was established with the species placed directly in the genus Poropanchax rather than a different genus first, the authority is not parenthesised. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) recognises the valid combination as Poropanchax stigmatopygus Wildekamp & Malumbres, 2004, within the family Procatopodidae — the African lampeye killifishes — a group distributed across tropical Sub-Saharan Africa from Senegal to East Africa.
The genus Poropanchax itself is characterised by the presence of a supraorbital photophore — a light-producing organ or iridescent reflective patch situated above or just behind the eye — that gives lampeyes their common name and their characteristic blue-green glint in ambient light. The genus currently encompasses a handful of small West and Central African species occupying forest streams and coastal lowland rivers.
The specific epithet combines the Greek stigma (a mark or spot) and pygus (the rump), together meaning 'marked rump' or 'spotted caudal peduncle' — a direct reference to the dark blotch on the caudal peduncle that is the species' most prominent field mark. No subspecies or geographic variants are formally recognised, though the American Killifish Association database records six distinct collection localities, suggesting some intraspecific geographic diversity that has not yet been formally analysed.
Morphology
Poropanchax stigmatopygus is a tiny, slender, and laterally compressed fish. FishBase records a maximum standard length of 1 in, placing it among the smallest members of the genus. The body is typical of a procatopodid lampeye: elongated and cylindrical in cross-section, with a relatively large eye set high on the head and a small, upturned mouth suited to surface and mid-water feeding. The characteristic lampeye feature — the iridescent patch of tissue above or just behind the eye — is present and produces the blue-green to silver shimmer that is a defining trait of the group.
Overall colouration is modest: the body is translucent to pale yellowish or straw-coloured, with the internal organs faintly visible through the flanks. The most conspicuous marking is the dark pigment blotch on the caudal peduncle — the feature commemorated in the species name — which stands out clearly against the otherwise pale body. Fins are colourless to faintly hyaline. Males tend to be slimmer and may show slightly more intense iridescence in the supraorbital patch; females are noticeably deeper-bodied when gravid, the abdomen rounding out conspicuously as eggs develop.
Habitat
The native range of Poropanchax stigmatopygus encompasses the coastal lowland and forest-margin freshwaters of West-Central Africa: Cameroon, Gabon, and Equatorial Guinea. The type locality is recorded from Cameroon. These are countries of high rainfall and extensive rainforest cover, and the species occupies the kinds of permanent, slow-moving or still waters — forest streams, swamp margins, shaded ditches, and the edges of larger rivers — that characterise that landscape.
As a procatopodid lampeye of West-Central African forest drainages, P. stigmatopygus inhabits waters that are typically soft, slightly acidic to neutral, and well-shaded by riparian vegetation. These conditions translate in the aquarium to temperatures of roughly 75–81 °F, pH in the moderately soft and acidic range, and water that is clear rather than blackwater-tannin-stained, reflecting the permanent-stream character of its habitat.
Being a non-annual species, it is not tied to ephemeral seasonal pools that dry out each year; instead it persists in permanent water bodies throughout the year, which shapes its reproductive strategy as a continuous spawner rather than a fish that must pack an entire reproductive cycle into a short wet season.
Feeding
Like most small lampeye killifishes, Poropanchax stigmatopygus is a micro-predator of invertebrates, feeding primarily on small aquatic and terrestrial insects, zooplankton, and other tiny invertebrates in the wild. The upturned mouth and the tendency to school near the surface or in mid-water are consistent with the foraging habits of surface-orientated procatopodids that key on drifting or emerging insects and on zooplankton.
In the aquarium, the small size of the fish constrains food choices: the mouth is tiny and the fish will not take large food items. Small live or frozen foods — Daphnia, baby brine shrimp (Artemia nauplii), micro-worm, and fine-grade dried foods designed for small fish — form the practical diet. A varied diet that includes live or frozen invertebrates promotes good condition, brings out colour and iridescence, and supports successful spawning. The fish is an active, surface-cruising feeder and will compete for food within a school without difficulty.
Mating
Poropanchax stigmatopygus is a non-annual, continuous egg-layer — a plant-spawner in the killifish hobbyist's terminology, meaning it deposits small numbers of adhesive eggs among fine-leaved aquatic plants or spawning mops over an extended period rather than producing a single mass-clutch in substrate intended for desiccation. This mode of reproduction is characteristic of procatopodid lampeyes and reflects the species' permanent-water habitat: there is no dry season that forces an annual life-history strategy.
Males court females with lateral displays that show off the iridescent supraorbital photophore patch to maximum effect — the blue-green glint presumably functions as a species and individual quality signal. Spawning occurs with male and female side by side, the male pressing close to the female as a single egg is fertilised and deposited at a time. In the aquarium, pairs or trios (one male, two females) will spawn repeatedly across many sessions provided conditions are right, with each session yielding only a handful of eggs.
Breeding
Breeding Poropanchax stigmatopygus in the aquarium is described by hobbyist sources as a somewhat difficult undertaking, the main challenge being poor egg survival rather than any complexity in inducing the fish to spawn. The adults will spawn freely in soft, moderately acidic water at 75–81 °F among fine plants or artificial spawning mops — Java moss or dense clumps of nylon spawning mops are the standard media. Eggs are small, adhesive, and deposited individually, one or a few per day over an extended period.
Egg survival is the bottleneck: the eggs are sensitive to fungal attack, and losses in poorly managed conditions can be high. Separating eggs to a separate rearing container — checking spawning mops every few days and moving eggs individually — is the standard approach. Slight methylene blue or alder-cone tannins in the rearing water can help reduce fungal loss. Hatching occurs after approximately two to three weeks depending on temperature. The fry are tiny at hatching and require infusoria or commercial fry powder as first foods before graduating to micro-worm and Artemia nauplii as they grow. Raising fry to juvenile size demands consistent attention to water quality and food availability, which explains the species' 'difficult' hobbyist rating.
In the aquarium
Despite the breeding challenge, Poropanchax stigmatopygus is a peaceful, active, and community-compatible species when kept with appropriately sized tankmates. It is a schooling fish and should be kept in groups of at least six to eight individuals; solitary or paired fish become shy and do not display well. The iridescent supraorbital flash that defines the lampeye group is best appreciated when the fish school in good light, the eye-patches catching the beam with each turn.
A small, well-planted tank of 10–15 US gal is adequate for a school. Soft, slightly acidic water (pH 6.0–7.0, low to moderate hardness) at 75–81 °F suits the species well. Gentle filtration is preferred — the fish are small and the flow should not overpower them. Dense plantings of fine-leaved species provide shelter and serve as natural spawning sites. Tankmates should be similarly sized and peaceful; any fish large enough to eat a 1 in killifish is unsuitable. Other small West African lampeyes, microrasboras, and small tetras of the same geographic region make compatible companions.
The American Killifish Association notes six collection localities in its database and records four articles in the JAKA literature, reflecting a modest but active hobbyist interest in the species among lampeye specialists. The fish's small size, peaceful disposition, and attractive schooling behaviour make it appealing to the specialist community, even if the egg-survival difficulty keeps it from wider mainstream distribution.
Conservation
The IUCN Red List assessed Poropanchax stigmatopygus as Least Concern (LC) in February 2009, a status reflecting that the species was not considered at elevated risk across its range in Cameroon, Gabon, and Equatorial Guinea at the time of assessment. The American Killifish Association rates all three countries as HIGH for the species' occurrence, suggesting a reasonably broad and stable distribution within its West-Central African range.
Nonetheless, forest-stream killifishes of West-Central Africa face a suite of background threats that do not disappear behind an LC label. Deforestation — for logging, agriculture, and palm oil cultivation — degrades the riparian forest cover that maintains the cool, shaded, soft-water conditions these fish depend upon. Siltation following land clearance chokes spawning vegetation and reduces water clarity. The Congo Basin and Gulf of Guinea coastal drainages where this species lives are subject to increasing pressure from agricultural expansion and large-scale extractive industries.
As a small-bodied, forest-associated specialist with a relatively restricted coastal distribution, P. stigmatopygus would be vulnerable to localised habitat loss even if regional population trends are currently stable. No specific monitoring or targeted conservation measures are documented for this species, and the 2009 assessment is now more than fifteen years old — updated data on population trends and habitat condition across its range would provide a firmer basis for conservation planning.