Taxonomy & naming
Aphyosemion teugelsi was described by Jouke Ruurd van der Zee and Ralf Sonnenberg in 2010, with the type locality recorded as Lukula Creek in the upper Wamba River basin, Kwango River drainage, southwestern Democratic Republic of Congo. The species is placed in the family Nothobranchiidae — the African killifishes — and the genus Aphyosemion, which encompasses the bulk of West and Central African non-annual lamp-eye and lyretail killifishes. Killi-Data Online and FishBase both confirm the combination Aphyosemion teugelsi van der Zee & Sonnenberg, 2010 as the current valid name per Eschmeyer's Catalog of Fishes.
The species was classified by the American Killifish Association in Class 12, which groups Aphyosemion and related genera, and received coverage in the Journal of the American Killifish Association (JAKA) in 2011. Its meristic data are: dorsal fin with 0 spines and 10–13 soft rays; anal fin with 0 spines and 14–15 soft rays; vertebrae 29 — a count consistent with other small-bodied Aphyosemion.
A diagnostic note recorded by FishBase sets this species apart from congeners by its particularly small size (approximately 1 in SL in males), anterior insertion of the dorsal fin (positioned above the anal fin origin), a longer dorsal fin base relative to related species, and black fin margins in males without the elongated caudal fin streamers that typify some other Aphyosemion. Whether populations from surrounding drainages belong to the same taxon has not been formally resolved.
Morphology
Males reach approximately 1 in standard length, making Aphyosemion teugelsi one of the smaller species in a genus where 1.5–2.5 in is more typical. The body form follows the general Aphyosemion pattern: slender, slightly compressed laterally, with a rounded snout, upturned mouth adapted for surface and mid-water feeding, and a slightly rounded caudal fin lacking the pointed extensions or lyretail lobes found in showier congeners.
In common with other Aphyosemion, males are significantly more colourful than females, displaying the characteristic vivid patterning and bold fin colouration of the genus. FishBase records prominent black fin margins in males — a diagnostic character used to separate this species from similar taxa within the Kwango drainage. The dorsal and anal fins lack extended filaments. Females are the typical drab brownish cryptic colour of female Aphyosemion, with minimal markings and unpatterned fins. The fin-ray counts (D 10–13; A 14–15) and vertebral count (29) are within the lower Aphyosemion range and reflect the species' small body size.
Habitat
The known range of Aphyosemion teugelsi is centred on the upper Wamba River basin in the Kwango River drainage of southwestern Democratic Republic of Congo — a region of mixed forest-savanna mosaic with a pronounced wet/dry seasonality. The type locality, Lukula Creek, is a small forest or gallery-forest stream; such streams in this part of the Congo Basin are typically slow-moving to almost stagnant in their upper reaches, shaded by overhanging vegetation, and characterised by soft, acidic water with low mineral content and moderate tannin staining from decomposing leaf litter.
Aphyosemion species in comparable habitats throughout West and Central Africa typically occupy surface and mid-water positions in water at 64–72 °F (65–72 °F), with pH often below 7 and conductivity low. The genus prefers shallow margins, root tangles, submerged vegetation, and areas of slow or negligible current where plant spawning is feasible. Because the Wamba-Kwango basin lies at moderate elevation (the upper drainage rises toward the Angolan plateau), seasonal temperature fluctuations may be somewhat greater than in equatorial coastal lowlands, but no species-specific water chemistry measurements are available in the published literature.
The Kwango drainage as a whole is notably rich in endemic killifishes; Aphyosemion teugelsi shares its basin with several other described and undescribed taxa, and the diversity of the upper Kwango in southwestern DRC and northern Angola remains incompletely documented.
Feeding
No published diet study for Aphyosemion teugelsi specifically is available. Its diminutive size — males at 1 in SL — constrains the range of prey it can handle and places it in the microinvertebrate and zooplankton feeding guild typical of small-bodied Aphyosemion. In the wild, species of comparable size in this genus take small aquatic and terrestrial invertebrates at or near the water surface: chironomid larvae, small worms, springtails, and similar prey.
In the aquarium, small non-annual Aphyosemion generally accept live and frozen Artemia nauplii, Daphnia, micro-worms (Panagrellus), and Grindal worms readily. Offering suitably sized live food is particularly effective for conditioning pairs prior to spawning. Prepared micro-pellets and crushed flake are accepted by acclimatised individuals. Given its tiny gape at 1 in, prey items should not exceed roughly 0.5 in in their largest dimension.
Mating
Aphyosemion teugelsi is a non-annual killifish whose reproductive strategy centres on continuous plant or mop spawning in permanent or near-permanent forest stream habitats. The eggs are not buried in substrate and do not undergo diapause; they are adhesive and are deposited on fine-leaved vegetation, root tangles, or synthetic spawning mops, where they develop uninterrupted in the water column.
Males court females with lateral displays, spreading the colourfully marked fins to accentuate the black fin-margin pattern. Courtship is typically brief: the male drives alongside the female, and the pair press together momentarily to deposit a single egg on a nearby plant or mop fibre before separating. Spawning proceeds over multiple sessions across days or weeks rather than in a single mass event, and a healthy pair in good condition can produce several eggs per day. The male can be persistent or aggressive in pursuit; providing cover for the female and a reasonably sized enclosure reduces the risk of harassment.
Breeding
Eggs of Aphyosemion teugelsi, like those of other non-annual Aphyosemion, are deposited individually on plant material or spawning mops and develop continuously in water at ambient temperature. At the temperatures typical of the genus (64–72 °F), incubation takes approximately two to three weeks, though no species-specific data have been published; breeders working with congeners in the same size class use a water incubation period of 14–21 days as a starting point.
For aquarium breeding, a small species or trio tank (one male, two females) furnished with Java moss, fine-leaved water plants, or nylon spawning mops provides a functional setup. Eggs can be collected by removing the mop or plants and either hatching them in a separate shallow container or leaving them in place if the adults are not consuming them. Newly hatched fry are very small and require infusoria or paramecia as first foods before transitioning to micro-worms and Artemia nauplii. As with all Aphyosemion, soft, slightly acidic water and meticulous tank hygiene are important; fry are sensitive to ammonia spikes during the first few weeks.
The American Killifish Association notes the species in its records for Class 12, indicating that captive keeping and breeding has been achieved in the hobby since at least 2011, though it remains a rarely traded species relative to more common Aphyosemion.
In the aquarium
Aphyosemion teugelsi is a specialist fish suited to experienced killifish keepers rather than general community aquaria. At 1 in SL for males, it is tiny and easily lost in heavily planted or decorated tanks; it requires calm, well-filtered water without strong current and should not be housed with larger or boisterous fish that will out-compete it for food or treat it as a meal.
A dedicated small species tank — 5.5–10 US gal is ample for a pair or trio — fitted with a tight-fitting lid (killifishes are accomplished jumpers), a gentle sponge filter, subdued lighting, and a cover of floating plants or cork bark to shade the surface provides ideal conditions. Water should be soft and slightly acidic to neutral (pH 6.0–7.0, low hardness, temperature 64–72 °F / 64–72 °F), reflecting the cool, shaded forest-stream conditions of the Wamba basin. Regular small water changes maintain quality without the large-volume changes that can stress small fish.
The species is not commercially produced in significant numbers and is primarily circulated within killifish clubs and specialised breeders. Hobbyists in Europe and North America with an interest in the less-common Central African Aphyosemion occasionally keep it, and the AKA has documented it since 2011. Its modest colour compared with showier lyretail congeners means it appeals mainly to those drawn to the scientific and behavioural interest of a small-bodied endemic species.
Conservation
Aphyosemion teugelsi has not been assessed by the IUCN Red List and carries a status of Not Evaluated. This absence of formal assessment is common for recently described, narrowly endemic killifishes from the Congo Basin; the group's taxonomic complexity and the limited resources available for comprehensive surveys of small-bodied fishes in remote drainages mean many species are described, published, and then left without a population estimate or threat assessment.
The species is known only from the upper Wamba River basin in the Kwango drainage of southwestern Democratic Republic of Congo — a region that, while less intensively deforested than the Congo Basin's western lowlands, faces ongoing pressures from subsistence agriculture, charcoal production, and artisanal land clearing. Small gallery-forest streams and headwater creeks — the preferred habitat of tiny Aphyosemion — are disproportionately affected by these pressures because their narrow riparian corridors provide little buffer against sedimentation, temperature rise, and altered hydrology when surrounding forest is removed.
Given the species' small known range, tiny size, and dependence on the specific water chemistry of shaded forest streams, it is prudent to regard it as potentially vulnerable even in the absence of a formal Red List assessment. Repeated collection surveys across the Wamba-Kwango system and neighbouring Angolan drainages are needed to clarify its true distribution and abundance before any meaningful threat status can be assigned.