Taxonomy & naming
Rhexipanchax lamberti was described by the Belgian ichthyologist Max Poll in 1971, with the type locality in the river systems of Guinea, West Africa. The authority appears in parentheses because the species was originally placed in a different generic combination before being transferred to Rhexipanchax. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) records the valid combination as Rhexipanchax lamberti (Poll, 1971).
The genus Rhexipanchax is a small lampeye genus within the family Poeciliidae (subfamily Procatopodinae), the African lampeye killifishes. Lampeyes were historically lumped under broader genera such as Aplocheilichthys, but a series of revisions in the 2000s broke that assemblage into multiple well-supported genera on morphological and molecular grounds. Rhexipanchax as currently understood accommodates a handful of West and Central African species with shared characters of body shape and the iridescent supraocular organ.
The specific epithet lamberti honours a person named Lambert, following a common nineteenth- and twentieth-century convention in ichthyological nomenclature of naming species for collectors, patrons, or colleagues. The American Killifish Association places R. lamberti in its Class 14 (All other Old World killifishes), the category that encompasses unusual West African lampeyes outside the better-represented genera.
Morphology
Lambert's lampeye is a small, slender fish reaching approximately 2 in total length (FishBase). The body is elongate and laterally compressed in the typical lampeye manner, with a pointed snout, a large eye, and a posteriorly placed dorsal fin that sits roughly above or just ahead of the anal fin — the characteristic silhouette of the procatopodine lampeyes.
The defining feature of all lampeyes is the iridescent photophore-like organ immediately above the eye. In R. lamberti this organ glows blue-green in good light, a structural colour produced by light-refracting tissue rather than pigment. When a school catches direct illumination the effect is conspicuous — a flicker of cold blue-green light along the waterline of the eye. The flanks are otherwise translucent to pale silvery-olive, and the fins are largely clear. Sexual dimorphism in colour is modest, as is typical for procatopodines, though males in prime condition often show stronger iridescence and somewhat more vivid finnage than females.
Habitat
Rhexipanchax lamberti is native to the upper drainage systems of three West African rivers in Guinea: the upper Gambia, the upper Bafing (a Senegal River tributary), and the upper Konkouré. These are highland stream systems descending from the Fouta Djallon plateau, characterised by clear, moderately fast-flowing water over sandy or rocky substrates, with marginal vegetation and roots providing shelter and spawning sites.
FishBase records the species in permanent, non-seasonal water — it is not an annual killifish and does not survive desiccation in diapause. The water chemistry parameters noted by FishBase centre around a temperature range of 72–82 °F and a pH of approximately 6.5, consistent with the soft, slightly acidic highland streams of Guinea. The species is therefore adapted to clear, oxygen-rich flowing water rather than the stagnant, oxygen-poor conditions tolerated by annual killifishes of savanna pans.
In the aquarium, the requirement for moderate water movement is confirmed by hobbyist sources (killi.co.uk): the fish thrives with gentle to moderate current, a parameter worth replicating in captive systems to maintain health and encourage natural schooling behaviour.
Feeding
Like most small procatopodine lampeyes, R. lamberti is a micro-predator and surface-feeder in the wild, targeting small invertebrates — insect larvae, microcrustaceans, and other zooplankton — at or near the water surface and in the water column. The relatively large eye and upturned mouth typical of the group are adaptations for detecting and capturing surface prey.
In captivity the species accepts small live and frozen foods readily: Daphnia, Artemia nauplii, micro-worms, and fine-grade dried foods are all suitable. Maintaining condition and colour in males benefits from regular offerings of live or frozen invertebrates. As a small fish with a correspondingly small gape, food particle size matters — appropriately sized foods are necessary to ensure adequate nutrition and to avoid waste that can degrade water quality in the relatively clean-water conditions this species requires.
Mating
Rhexipanchax lamberti is a non-annual, continuous spawner — a plant-spawner in killifish terminology, meaning it deposits small numbers of adhesive eggs among fine-leaved vegetation, spawning mops, or fibrous roots over an extended period rather than burying eggs in substrate for diapause. This is the standard reproductive mode for procatopodine lampeyes of permanent-water habitats.
Males display to females with spread fins and lateral posturing, the iridescent supraocular patch catching the light during courtship. Pairing is temporary: a male accompanies a ripe female through vegetation or a spawning mop, and the pair presses together briefly as one or a few adhesive eggs are released and fertilised. The eggs are attached to plant fibres or mop strands by a sticky filament. This process is repeated continuously over days and weeks, with females producing small batches of eggs on a near-daily basis when well-conditioned. Killi.co.uk notes successful breeding at 61–66 °F and neutral pH, which corresponds well with the cooler end of the species' highland range.
Breeding
Because eggs are laid singly or in small numbers over an extended period rather than in a single clutch event, breeding R. lamberti in captivity is straightforward once a colony is established. The standard method uses fine-leaved plants (Java moss, hornwort) or synthetic spawning mops placed in the tank; eggs are picked from the mop every few days and incubated separately, or the mop itself can be transferred to a small rearing vessel.
Eggs hatch in approximately 10–14 days at 72–75 °F, producing tiny larvae that become free-swimming shortly after. First foods should be appropriately small: infusoria, vinegar eels, or commercial fry powder for the first several days, followed by freshly hatched Artemia nauplii as the fry grow. Because adults will eat eggs and newly hatched fry, separate rearing is strongly recommended. Killi.co.uk reports the species suitable for planted aquariums and identifies it as a good subject for hobbyist breeding projects, though it notes the fish's requirements for clean, moving water must be maintained through the breeding process as well.
In the aquarium
Lambert's lampeye is a small, peaceful schooling fish best kept in groups of six or more, where the collective movement and the flash of supraocular iridescence are most visible. It is suited to a species aquarium or a community of similarly sized, non-boisterous fish; its small size makes it vulnerable to fin-nippers and predators, and its preference for clear, moderately flowing water narrows the choice of compatible species toward those sharing similar water-quality requirements.
FishBase describes the species as very difficult to maintain, while killi.co.uk takes a more optimistic view, rating it suitable for planted aquariums with appropriate conditions. The discrepancy likely reflects water quality: the species is intolerant of the elevated nitrate and low-oxygen conditions typical of stagnant or infrequently maintained tanks, but in a well-filtered, moderately flowing system with regular partial water changes it performs well. Temperature in the 72–79 °F range and pH around 6.5–7.0 reflect its highland-stream origin. The tank should be well-planted and covered — lampeyes are accomplished jumpers.
In the killifish hobby the species is encountered mainly through specialist killifish societies and club fish auctions rather than general aquarium retail. The American Killifish Association photo gallery documents captive specimens and three JAKA (Journal of the American Killifish Association) articles provide practical husbandry information for those seeking detailed guidance.
Conservation
The IUCN Red List assessed Rhexipanchax lamberti as Least Concern (LC) in April 2020, based on its distribution across multiple river drainages in Guinea and the absence of evidence for rapid population decline. The species' occurrence across the upper Gambia, upper Bafing, and upper Konkouré systems provides some buffer against localised threats, as no single drainage holds the entire population.
Nonetheless, the highland watersheds of the Fouta Djallon in Guinea face mounting anthropogenic pressure: deforestation for agriculture and charcoal production has accelerated erosion and sedimentation of clear highland streams, and small-scale mining activity in the region contributes turbidity and chemical contamination to waterways. These changes degrade the clear, moderately flowing stream habitats that R. lamberti requires and that it cannot substitute with more tolerant alternatives, unlike the annual killifishes of savanna pans which persist through desiccation. The species' sensitivity to water quality means that habitat degradation, even without direct exploitation, represents the primary long-term risk.
No targeted conservation measures are known for the species. Continued monitoring of the Guinea highland stream systems, particularly in the context of accelerating land-use change, would be warranted given the species' dependence on intact forest-stream habitat quality.