Taxonomy & naming
Hylopanchax leki was formally described by van der Zee, Sonnenberg & Schliewen in 2013 in Zootaxa 3701(1):35–53, in a paper titled 'Description of three new species of Hylopanchax Poll & Lambert, 1965 from the central Congo basin (Cyprinodontiformes: Poeciliidae: Procatopodini) with a redefinition of the genus.' The holotype (ZMS 40764) was collected within or near Salonga National Park; FishBase records the type locality as the Lokoro River near Lompolé, within the Mai Ndombe system of the middle Congo River basin, Democratic Republic of the Congo.
The genus Hylopanchax belongs to the tribe Procatopodini within the family Poeciliidae — the group of African lampeye killifishes characterised by the iridescent photophore-like patch above the eye. Catalog of Fishes (Fricke, Eschmeyer & Fong) recognises the valid name as Hylopanchax leki van der Zee, Sonnenberg & Schliewen, 2013. The species is assigned to AKA (American Killifish Association) Class 14 (All Other Old World).
The epithet leki comes from the Lingala word meaning 'smaller younger sibling', chosen by the authors to reflect that H. leki is the smallest species in the genus and occurs sympatrically with the slightly larger H. ndeko. The species can be distinguished from H. ndeko by the dark orange colouration of the snout, lower jaw, and anterior throat — versus the yellow in H. ndeko — in addition to differences in meristic counts and body proportions.
Morphology
Hylopanchax leki is one of the smallest members of its genus, with FishBase recording a maximum standard length of 1 in for males and unsexed specimens. The body is relatively deep for the genus — a characteristic cited in the original description alongside the meristic counts that separate H. leki from its congeners: 11–13 dorsal soft rays, 18–20 anal soft rays, and a total of 30 vertebrae.
Colouration in life is notable for the dark orange flush of the snout, lower jaw, and anterior throat, a feature that readily distinguishes this species from the sympatric H. ndeko (which carries yellow in those areas). As in all lampeyes, both sexes display the iridescent blue-green or silvery patch positioned just above the eye — the eponymous 'lamp' from which the group takes its common name. This photophore-like ocellus is believed to play a role in intraspecific recognition and courtship under the dim canopy light of rainforest streams.
Full colour descriptions of females and juveniles in life, and detailed osteological data, are in the original Zootaxa publication; field material is limited and hobbyist-kept specimens have not been widely documented, so colour notes beyond those in the type description remain sparse.
Habitat
The type locality is a small, shady stream associated with the Lokoro River system near the village of Lompolé, within or on the edge of Salonga National Park — the largest tropical rainforest reserve in Africa and one of the most remote. The Mai Ndombe drainage that feeds the Lokoro is part of the middle Congo River basin, characterised by heavily shaded, tannic-stained forest streams with soft, moderately acidic water and dense overhanging and submerged riparian vegetation.
FishBase classifies the habitat as freshwater, pelagic (water-column dwelling rather than benthic), and tropical. Like other West and Central African lampeyes of forested drainage systems, H. leki almost certainly inhabits the upper water layers of small permanent streams, sheltering among marginal vegetation, submerged roots, and leaf litter. Salonga's forest streams are typically low in dissolved minerals, with temperatures tracking the shaded ambient conditions of the equatorial rainforest — likely in the range of 73–81 °F, though no published water-chemistry measurements from the type locality are available.
The species is known only from the type locality. Whether it occurs more broadly in the Lokoro system or adjacent drainages within Salonga National Park remains uninvestigated.
Feeding
No published diet study exists for Hylopanchax leki specifically. Inference from the foraging ecology of other small procatopodine lampeyes, combined with its pelagic water-column habit, suggests a diet centred on small invertebrates: microcrustaceans, insect larvae, emergent insects fallen onto the water surface, zooplankton, and similar prey accessible in the upper water column of shaded forest streams.
In an aquarium setting, small-mouthed lampeyes of similar size are typically offered live or frozen Artemia nauplii, micro-worm, Daphnia, and finely crushed dry foods. Given H. leki's maximum size of under 1 in, food items must be proportionally small; it would be unable to take the larger invertebrate prey accessible to bigger killifish. Prey selection in the wild is likely partly influenced by the low-light conditions of its shaded stream habitat, where visual acuity at dawn and dusk may be aided by the iridescent eye-spot.
Mating
Hylopanchax leki is a non-annual lampeye — it inhabits permanent forest streams and does not produce diapausing eggs. Its reproductive strategy follows the continuous egg-layer pattern typical of the tribe Procatopodini: pairs or small groups spawn repeatedly over extended periods, depositing small numbers of adhesive eggs among fine-leaved aquatic plants, moss, submerged roots, and fibrous substrate at intervals rather than in a single mass spawning event.
The iridescent eye-spot is widely considered a courtship signal in procatopodine lampeyes. Males likely display the eye-patch to females under the dim forest canopy, where the bright ocellus stands out against the body colouration. Spawning is probably preceded by a brief pursuit or parallel-swimming display, as documented in related lampeye species, with the male aligning alongside the female to simultaneously release eggs and sperm onto or among the chosen substrate.
Because H. leki exists only as type material and is essentially unknown in the aquarium hobby, direct observations of courtship in this species have not been published.
Breeding
As a non-annual procatopodine, Hylopanchax leki produces small batches of adhesive eggs deposited continuously over time rather than a single seasonal clutch. The eggs attach to fine plant matter, moss, or root fibres and hatch after a period of several days (the precise incubation time is undocumented for this species; related lampeyes in similar temperature ranges typically hatch in 10–16 days). Fry are small at hatching and require appropriately fine first foods.
In aquarium practice, related lampeyes of comparable size are bred in species tanks with clumps of fine-leaved plants (Java moss, Riccia, hornwort) or spawning mops; eggs are collected by removing the mop and incubating separately, or by maintaining the tank with sufficiently dense plant cover that a small percentage of fry survive the adults' casual predation. Gentle, soft, slightly acidic water mimicking the shaded forest stream environment is recommended. There are no published aquarium breeding records specific to H. leki.
In the aquarium
Hylopanchax leki is essentially unknown in the aquarium hobby. Given its restricted range, its occurrence deep within a remote protected area, and the logistical difficulty of collecting within Salonga National Park, it is unlikely to appear in the trade without deliberate scientific collecting expeditions.
If it were maintained, the husbandry requirements would mirror those of other small soft-water Central African lampeyes: a densely planted nano or small species tank, soft and slightly acidic water (pH 6.0–7.0, low mineral content), subdued lighting simulating the shaded forest stream environment, and a gentle flow with good oxygenation. At under 1 in maximum, it is a candidate for micro-tanks of 5.5–10 US gal kept as a species or with very small peaceful companions. Live or frozen microfoods would form the core diet.
The American Killifish Association lists it under Class 14 (All Other Old World), which would govern show classification if hobbyist specimens ever became available. Its rarity and the remoteness of its habitat make it a species of primarily scientific interest at present.
Conservation
Hylopanchax leki has not been evaluated by the IUCN Red List and carries a status of Not Evaluated (NE). This reflects the species' very recent description (2013) and limited distribution data rather than any positive assessment of its security. The species is known from a single locality — a small stream near Lompolé within the Lokoro River system — inside or adjacent to Salonga National Park.
Salonga National Park is a UNESCO World Heritage Site covering approximately 36,0 mi² and represents some of the best-protected primary rainforest in the Congo basin. In principle, this provides the type locality with significant legal protection. However, Salonga has faced ongoing pressures including illegal poaching, artisanal mining activity within its boundaries, and the logistical difficulties of enforcement across such a vast and remote area. The forest streams that support microhabitat specialists like H. leki are locally sensitive to any disturbance of riparian vegetation or water quality.
Given its known distribution of a single locality and its dependence on the intact shaded forest stream environment, a formal IUCN assessment would be warranted. Based on IUCN criteria, a single-locality endemic with no documented population size and an area of occupancy potentially well under 6 mi² could qualify for threatened listing. The absence of any aquarium population means ex-situ conservation is not available as a safety net. Documentation of additional populations within the Lokoro drainage or elsewhere in the Congo basin would substantially alter the conservation picture.