Taxonomy & naming
Hylopanchax moke was described by van der Zee, Sonnenberg & Schliewen in 2013 in Zootaxa 3701(1):35–53, as one of three new species of the genus Hylopanchax Poll & Lambert, 1965 from the central Congo basin (Cyprinodontiformes: Procatopodidae: Procatopodini). The holotype is catalogued at the Musée Royal de l'Afrique Centrale under MRAC 102524, with paratypes MRAC 102525–102532; all material originates from the Congo interior between the Tshuapa and Kasai river systems. The Catalog of Fishes (Eschmeyer, Fricke & van der Laan) recognises van der Zee, Sonnenberg & Schliewen, 2013 as the authority.
The genus Hylopanchax takes its name from a compound of Greek hylē (wood, forest, material) and the older genus name Panchax (Meinken, 1932), a combination that evokes the forested stream habitats the group favours. The species epithet moke is a Lingala word meaning 'very small', a direct allusion to the minute adult size that sets this species apart even within a genus of small fishes. The American Killifish Association lists the species under its Old World killifish class (Class 14) without a recorded common name in the hobby.
Morphology
Hylopanchax moke is an extremely slender fish with a maximum recorded standard length of 1 in (1 in SL), making it one of the most diminutive members of the family Procatopodidae. Its most diagnostic character is body depth: at 16.3–20.0% of standard length it is conspicuously more compressed laterally than other Hylopanchax species, whose depth ranges from 20.8 to 35.5% SL. The dorsal profile of the back is nearly straight, giving the fish a pencil-like silhouette quite distinct from the gently arched back of most lampeyes.
Meristic counts recorded in the description are 6–7 dorsal soft rays, 15–17 anal soft rays, and 31 vertebrae. The light organ above the eye — the structural iridophore patch characteristic of all lampeyes and responsible for the group's common name — is present and produces the blue-green reflective sheen typical of the Procatopodini. Coloration details in preserved material are limited, but in life the body is likely translucent to silvery as in related forest-stream species, with the ocular light organ providing the most conspicuous field mark.
Habitat
Hylopanchax moke is known from the central Congo basin of the Democratic Republic of Congo, specifically from the zone between the Tshuapa and Kasai rivers. The AKA records collection localities at Lui Kotale and Liombo, both in the DRC. FishBase characterises the species as inhabiting the calmer portions of larger forest streams — a freshwater, tropical environment consistent with the lowland rainforest rivers of the interior Congo.
As a permanent-water lampeye, H. moke is associated with clear, well-oxygenated water in forest-shaded stream settings rather than seasonal pools. The dense canopy cover typical of its habitat reduces water temperature fluctuation and contributes fine particulate matter and submerged plant roots that lampeyes use for egg deposition. Precise water-chemistry data for this species' specific localities have not been published, but comparable central Congo forest streams are typically soft and slightly acidic, with low conductivity and moderate temperatures consistent with equatorial lowland conditions.
Feeding
Specific dietary data for Hylopanchax moke have not been published, but the feeding ecology of lampeyes more broadly is well characterised. Small Procatopodidae are micro-predators and planktivores, taking zooplankton, small aquatic invertebrates, insect larvae, and emerging midges at the water surface. Their small mouth gape constrains prey to appropriately minute items. The calm forest-stream margins and root tangles that constitute their preferred habitat provide a rich supply of microfauna.
In aquarium conditions, lampeyes of comparable size are maintained on a varied diet of live and frozen small invertebrates — Daphnia, Cyclops nauplii, baby brine shrimp, and micro-worm — supplemented by quality dry foods of appropriately small particle size. Given H. moke's minute adult length (under 1 in), only very fine-grade foods are suitable, and live zooplankton cultures are recommended for conditioning breeding stock.
Mating
Hylopanchax moke is a non-annual lampeye — a continuous spawner of permanent water that does not undergo embryonic diapause. Like most Procatopodidae, it belongs to a reproductive guild of small schooling fishes that deposit a few adhesive eggs at a time over an extended spawning period, attaching them singly or in small clusters to fine-leaved aquatic plants, floating roots, moss, or other fibrous substrate at or near the water surface.
In this mode there is no defined spawning season or courtship peak tied to a dry-season die-off; pairs or small groups spawn repeatedly and gradually through the year as conditions allow. Males display to females with the iridescent ocular light organ and a lateral spread of the body, behaviours common across the Procatopodini. There is no parental guarding of eggs or fry.
Breeding
As a non-annual plant-spawner, Hylopanchax moke lays small numbers of adhesive eggs over extended periods rather than producing a single large clutch. Eggs are attached individually to fine plant matter, moss, or root fibres, where they incubate in the ambient water. In species of comparable size in the family, incubation at tropical temperatures of around 75–79 °F typically runs one to two weeks, with fry hatching as free-swimming larvae that require very fine first foods.
In the aquarium, a breeding setup for miniature lampeyes of this type typically employs a thickly planted small tank or a container with floating java moss and a gentle sponge filter. Spawning mops are a useful analogue for natural vegetation. Eggs can be collected and incubated separately to protect them from adult predation, or adults can be removed after a period and the mop transferred to a rearing vessel. Fry are tiny at hatching and require infusoria or commercial micro-fry powder before graduating to nauplii.
In the aquarium
Hylopanchax moke is essentially unknown in the European or North American aquarium trade and remains a species kept almost exclusively by specialist killifish hobbyists with access to field-collected or carefully propagated stock. Its minute adult size (under 1 in SL) makes it one of the smallest killifishes that could realistically be maintained, and it demands correspondingly small, calm aquaria with gentle filtration and no tankmates large enough to regard it as prey.
A species tank or a biotope setup reproducing central Congo forest-stream conditions suits it best: soft, slightly acidic, warm water (approximately 75–81 °F), subdued lighting, floating plants or submerged root fibres providing cover and spawning substrate, and an absence of surface turbulence. Given the limited availability of this fish and its narrow known range, any captive population carries disproportionate conservation value, and responsible breeders are encouraged to document collection data and maintain distinct locality lines.
Conservation
Hylopanchax moke has not been formally assessed by the IUCN Red List and carries a Not Evaluated (NE) status as of 2026. This is not an indication of security: the species' entire documented range lies within a small zone of the central Congo basin between the Tshuapa and Kasai rivers, a remote interior region that has received little ichthyological survey effort. With a known adult size under 1 in and apparent restriction to calmer forest-stream habitats, it is likely a genuinely range-restricted species vulnerable to the pressures affecting Congo basin lowland forests broadly: agricultural expansion, artisanal logging, and the gradual conversion of closed-canopy forest to open land that increases sedimentation and alters the clear-water stream conditions forest lampeyes require.
The Congo basin hosts one of the world's highest densities of freshwater fish endemism, and many narrow-range killifishes of the Procatopodidae are poorly represented in museum collections and entirely absent from trade. Formal assessment of H. moke — even a preliminary one to determine whether it qualifies for a threatened category — would require targeted field surveys of its known localities and a broader search of adjacent stream systems in the Tshuapa–Kasai interfluve.