Taxonomy & naming
Rhexipanchax kabae was described by Jacques Daget in 1962 from material collected in the Kaba River, a tributary of the Mamou drainage system in what is now central Guinea. Eschmeyer's Catalog of Fishes recognises the valid combination as Rhexipanchax kabae (Daget, 1962), the parenthetical authority indicating that the species was originally placed in a different genus before being transferred to Rhexipanchax.
Rhexipanchax is a small West African killifish genus within the tribe Procatopodini (family Poeciliidae sensu lato, or placed in Aplocheilidae by some authorities), a grouping of small, schooling egg-layers collectively known as lampeyes for the iridescent blue-green light-organ patch above the eye. The genus name combines the Greek rhexis (rupture, fragmentation — referencing the lateral line system or the fragmented, patchy distribution of the group) with Panchax, an older generic name long applied to Old World egg-laying killifishes. The species epithet kabae is a Latinised toponym derived from the Kaba River (also rendered Kabae), the type locality in the Mamou drainage of Guinea.
The species is recognised as distinct from its closest relative and near-range congener Rhexipanchax lamberti, which shares the Guinean Forests hotspot and Vulnerable status. Both species have limited distributions in the upper Guinea highlands and are regarded as valid by current authorities.
Morphology
Rhexipanchax kabae is a slender, laterally compressed killifish of modest dimensions — the IUCN assessment gives a maximum length of 1.5 in TL, while FishBase records up to 2 in TL, a discrepancy likely reflecting individual variation and the difficulty of collecting maximum-sized individuals in the field. The dorsal fin carries 9–10 rays and the anal fin 16–17 rays, a fin formula consistent with other Procatopodini lampeyes.
Colouration is sexually dimorphic and characteristic of the group. Males are pale yellow-olive with a light blue iridescence that strengthens along the sides between the pectoral fin insertion and the dorsal fin origin, giving the impression of a metallic sheen in angled light. Females are translucent pale grey, subdued by comparison but still attractive in a school. Both sexes share the defining lampeye character: a bright, vivid blue reflection in the upper portion of the iris, produced by a specialised reflecting tissue (the lampeye light organ) positioned above the pupil. This retro-reflective iris patch is the group's most consistent field mark and the source of the collective common name.
Habitat
Rhexipanchax kabae inhabits small, permanent rivers, streams, and creeks in the upper Guinea highlands of West Africa. Its known range spans the Kaba River within the Mamou drainage system and the upper reaches of the Little Scarcies River system, covering parts of Guinea and Sierra Leone. The IUCN assessment documents an extent of occurrence of 7,347 mi² and an area of occupancy of 1,331 mi², with 6–10 estimated locations — a genuinely restricted range even by West African small-stream standards.
The species is benthopelagic and non-migratory, living in the water column close to the bottom and in mid-water of shaded forest streams. Like most West African lampeyes it favours clear, well-oxygenated water under forest canopy, where leaf litter and submerged roots provide shelter and microhabitat. Water temperatures in the upper Guinea highlands conform to the 64–79 °F range typical of this elevation and latitude. These are permanent water bodies — not seasonal pools — consistent with the non-annual life history of all Procatopodini lampeyes, which lack the diapausing egg stage that annual killifishes use to survive dry-season desiccation.
Feeding
Rhexipanchax kabae feeds in the manner typical of small West African procatopodid lampeyes: it is a micropredator and invertivore, picking small aquatic invertebrates, insect larvae, zooplankton, and surface-fallen insects from the water column and from the film at or just below the surface. Its upturned or terminal mouth and slender body are well adapted to feeding near the surface and in midwater, and in nature it likely schools loosely with conspecifics and exploits the abundant invertebrate drift of shaded forest streams.
In the aquarium, Rhexipanchax kabae and other lampeyes accept a variety of small live and frozen foods — Daphnia, Artemia nauplii, micro-worms, and finely chopped frozen bloodworm — as well as quality micro-pellets and flake small enough to fit the modest gape. Feeding at the surface and in mid-column is characteristic; sinking foods may be ignored. Regular, varied feeding supports the best colouration and condition in adult males.
Mating
As a non-annual lampeye of the tribe Procatopodini, Rhexipanchax kabae reproduces in a continuous or near-continuous mode rather than in a single synchronised annual burst tied to a dry season. Spawning is spread across an extended period, with adults in permanent stream habitat able to breed throughout the year given adequate food and stable conditions — a reproductive strategy consistent with life in water bodies that do not dry seasonally.
Males display to females with lateral posturing and spread fins, showing off the blue flank iridescence and the bright iris reflection. Courtship is brief and opportunistic. Females select among displaying males in a manner common to procatopodid lampeyes, and spawning pairs separate quickly after egg deposition. The mating system is polygamous and promiscuous, with no pair bond formation.
Breeding
Rhexipanchax kabae is a plant-spawner in the broad sense: pairs deposit small numbers of adhesive eggs among fine-leaved plants, submerged roots, filamentous algae, or other fibrous substrate at each spawning event, returning to spawn again over days and weeks. This trickle-spawning pattern, producing a few eggs at a time over a long period, is characteristic of the Procatopodini. Eggs are relatively large for the fish's size — typical of the group — and hatch in 10–14 days at tropical temperatures; the fry are immediately free-swimming and large enough to take Artemia nauplii as first food.
In the aquarium, breeding is most easily achieved by maintaining a well-conditioned group (one male to two or more females) in a thickly planted tank with Java moss, fine-leaved stem plants, or spawning mops. Eggs may be left in situ in a species tank with minimal predation risk, or removed on the plant substrate to a shallow rearing vessel. Parental care is absent — adults ignore eggs and fry alike. Fry grow steadily and can be raised on a progression of Artemia nauplii, micro-worms, and finely powdered dry food over the first weeks of life.
In the aquarium
Rhexipanchax kabae is a delicate and attractive West African lampeye suited to the small species or biotope aquarium. It is rarely encountered in the hobby trade — the American Killifish Association records the species under Class 14 (All other Old World killifishes), and two articles in the Journal of the American Killifish Association document it — but specialist West African killifish enthusiasts and importers occasionally make it available. The AKA also notes the species appears in both national and international ornamental fish commerce.
A tank of 10–15 US gal is sufficient for a small group. Soft to moderately soft, slightly acidic to neutral water (pH 6.5–7.2, temperature 68–77 °F) with good but gentle filtration suits the species well; the fine, clear streams it inhabits naturally have moderate flow and good oxygenation. Dense planting is important both for spawning and for the shy adults' sense of security. Rhexipanchax kabae is peaceful and best kept with other small West African species or in a species-only setup; large or boisterous tankmates stress the fish and suppress colouration. Males are at their best in small groups of two to three males with proportionally more females, showing off the blue iridescence in mutual display without the injury risk of one-to-one confined pairs.
Conservation
The IUCN Red List assessed Rhexipanchax kabae as Vulnerable (VU) under criteria B1ab(iii)+2ab(iii) in a 31 March 2020 evaluation by assessors Diallo and Lalèyè. The criteria reflect a small and restricted range — extent of occurrence of 7,347 mi² and area of occupancy of 1,331 mi² — combined with a continuing decline in the extent and quality of the species' freshwater habitat. The assessment identifies 6–10 locations, a low figure that makes the species sensitive to localised threats.
The primary threats are landscape-scale and systemic: deforestation of the upper Guinea highland forests, agricultural expansion and associated run-off, mineral exploitation (artisanal and industrial mining is active in parts of the Mamou and Little Scarcies drainages), and urbanisation around Guinea's interior towns. All of these forces degrade stream water quality, increase siltation, and reduce riparian canopy cover — changes that directly harm a small, clear-water forest-stream specialist like R. kabae. The IUCN portal for West African freshwater biodiversity lists R. kabae alongside its congener Rhexipanchax lamberti as threatened killifishes of the Guinean Forests biodiversity hotspot, a region under high and continuing deforestation pressure.
No formal protected area network is known to cover the core range of R. kabae in Guinea, and no captive-assurance colony programme has been documented. Specialist killifish societies in Europe and North America represent the primary custodians of the species outside its native range. Given the species' restricted distribution and the ongoing drivers of decline, monitoring of known stream localities and any expansion of protected riparian areas in the upper Guinea highlands would be the most direct conservation interventions.