Taxonomy & naming
Lacustricola pumilus was described by George Albert Boulenger in 1906. The authority is presented in parentheses, indicating the species has been moved from the original genus under which Boulenger placed it. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) treats the valid combination as Lacustricola pumilus (Boulenger, 1906).
The genus Lacustricola is a West and Central African lampeye assemblage placed within the family Procatopodidae (or, in some classifications, within an expanded Poeciliidae). Lampeyes are characterised by the iridescent supraocular photophore — a patch of light-reflecting tissue above each eye — and Lacustricola is among the more species-rich genera within the group, distributed across riverine and lake-fringe habitats of sub-Saharan Africa.
The specific epithet pumilus is Latin for 'small' or 'dwarf', a straightforward descriptor for a species that ranks among the smaller members of an already small-bodied genus. No subspecies are currently recognised, and no major taxonomic revisions of the species have been published since the original description.
Morphology
Lacustricola pumilus is a slender, laterally compressed killifish reaching an estimated maximum of approximately 1 in standard length, in line with other small members of the genus. The body form is typical of the lampeye group: elongate and fusiform, with a slightly upturned mouth adapted to feeding at or near the water surface, a rounded caudal fin, and relatively large eyes set high on the head.
The defining character of the species and genus is the iridescent supraocular light organ — a patch of specialised tissue just above the pupil that catches light and reflects it as a blue to blue-green glow. This structure is more strongly developed in males and is thought to function in species recognition and intraspecific signalling within the lampeye group. Male colouration is generally more vivid, with subtle iridescent flank scaling; females are plainer and noticeably deeper-bodied when gravid.
Sexual dimorphism is present but moderate. Beyond the stronger light-organ iridescence, males in breeding condition may show enhanced body iridescence and slightly more elaborate fin edges compared to females. Because L. pumilus has not been the subject of detailed morphometric study in the published literature, precise fin-ray counts and colour descriptions from live specimens remain incompletely documented.
Habitat
Lacustricola pumilus inhabits the clear, permanent, lowland freshwater streams and forest-margin waters of West Africa. The genus broadly favours well-oxygenated water over sand or leaf-litter substrates with marginal or overhanging vegetation, including roots, grasses, and fine-leaved aquatic plants that serve as spawning substrate. Water conditions in these forest-stream habitats are typically neutral to slightly acidic, with moderate hardness and stable temperatures through the year.
Temperature in the native range is estimated at approximately 75–79 °F, reflecting the equatorial West African lowland climate; pH is typically in the range 6.0–7.0. Unlike annual killifishes of savannah and seasonal-pool environments, Lacustricola pumilus occupies permanent waters and does not experience the dry-season desiccation that drives diapause in annual species.
The species is naturally a surface and mid-water fish, using the upper water column where its upturned mouth and light organ are most effective. Dense marginal vegetation and surface cover appear to be important habitat components, both as foraging sites for small invertebrates and as protection from aerial predators.
Feeding
In the wild, Lacustricola pumilus feeds on small invertebrates taken at or near the water surface, consistent with the feeding ecology of the genus. Small zooplankton — copepods, cladocerans such as Daphnia — insects that have fallen onto the water surface, and similar microinvertebrates constitute the natural diet. The upturned mouth is well adapted to seizing prey from the surface film.
In the aquarium, live and frozen small live foods including baby brine shrimp, Daphnia, copepods, and micro worms are readily accepted and are ideal for conditioning. The species is sufficiently small that large or coarse dried foods are unsuitable; finely ground or micro-pellet formulations that the fish can take at the surface are more appropriate. Variety in diet, including regular live or frozen zooplankton, helps maintain condition and brings fish into breeding readiness.
Mating
Lacustricola pumilus is a non-annual continuous spawner — a fundamental distinction from the annual killifishes of seasonal pools. There is no diapause, no soil-spawning, and no dormant egg phase. Instead, males court females over an extended period, with mating distributed across many small spawning events rather than concentrated in a single seasonal burst.
Male courtship in lampeyes typically involves display of the iridescent supraocular light organ, lateral body flashing, and fin spreading toward the female. The light organ is the species' primary visual signal, and its effectiveness in low-light, vegetated stream habitats is likely significant. Courtship in Lacustricola species is generally non-aggressive and brief, leading rapidly to a spawning clasp among plants or fine-leaved substrate.
Breeding
Lacustricola pumilus deposits small numbers of adhesive eggs at each spawning event, attaching them to the stems and leaves of fine aquatic plants, moss, or root tangles. This plant-spawning strategy, spread across many spawnings over an extended period, is typical of the non-annual lampeye group. Eggs hatch after a few days at tropical temperatures; the larvae are small and require suitably fine first foods.
In the aquarium, spawning is encouraged by providing dense fine-leaved plants (Java moss, floating plants, or spawning mops) and good water quality with regular small water changes. The adults will eat eggs and fry if left in the same tank; separating the spawning mop or transferring eggs to a rearing vessel is standard practice. A small number of fry per spawning event is characteristic, but spawning recurs frequently, building population over time. Fry accept infusoria and micro-foods from free-swimming, graduating quickly to freshly hatched brine shrimp nauplii.
In the aquarium
Lacustricola pumilus is a peaceful, schooling lampeye best kept in groups of six or more individuals where the social dynamics of the species — including male light-organ displays — can be observed. A species-only or carefully chosen community with other similarly sized, peaceful fishes is appropriate; robust or nippy tankmates will stress this delicate, small-bodied species.
Tank setup should replicate the species' natural stream habitat: clean, well-oxygenated water, gentle filtration that does not produce strong turbulence, and abundant fine-leaved plants or floating cover. Temperature 75–79 °F and pH 6.0–7.0 suit the species. Subdued lighting enhances the iridescent light-organ effect, making the fish significantly more attractive in a dimly lit planted tank than under strong illumination.
This species is not widely available in the mainstream hobby and is most often encountered through killifish specialist societies and hobbyist networks. Its small size, peaceful temperament, and attractive light-organ display make it a rewarding subject for the specialist aquarist interested in African killifishes. Dedicated attention to live and frozen food variety and water quality are the main requirements for long-term success.
Conservation
Lacustricola pumilus has not been formally assessed by the IUCN Red List and carries Not Evaluated (NE) status. The absence of an assessment does not imply security: many small West African endemics with restricted ranges remain unevaluated simply because assessment resources have not yet been directed to them.
The principal threats facing West African lowland freshwater fish of this type include deforestation and associated sedimentation and water-temperature increases in forest streams, conversion of forest-margin land to agriculture, and degradation of riparian vegetation that these surface-oriented, plant-spawning species depend on for reproduction. The permanent-water habitat of Lacustricola pumilus is less immediately vulnerable to the seasonal drying that threatens annual killifishes, but chronic habitat degradation and narrowing of the geographic range are real concerns for a species with limited distribution.
Collection pressure for the ornamental trade is generally modest for obscure lampeye species; the greatest long-term risk is the incremental loss of intact lowland forest-stream habitat across West Africa. A formal IUCN assessment with current distribution data would be a valuable step toward understanding the conservation position of this species.