Taxonomy & naming
Nanochromis teugelsi was described by Anton Lamboj and Robert C. Schelly in 2006, in the journal Ichthyological Exploration of Freshwaters (volume 17, number 3, pages 247–254). The holotype (AMNH 233373) was collected at Bokoni village on the Kasai River, Bandundu Province, Democratic Republic of the Congo, and paratypes are held at the American Museum of Natural History (AMNH), the Royal Museum for Central Africa in Tervuren (MRAC), and the Natural History Museum Vienna (NMW).
The species was confirmed as valid by Stiassny and Schliewen (2007). Its placement in Nanochromis is secure: it shares the genus-level characters of compressed body, the Pseudocrenilabrinae subfamily affiliation, and the west-central African freshwater distribution. Within the genus, the dwarfcichlid.com overview (2022) classifies Nanochromis teugelsi as a lacustrine/fluvio-lacustrine species alongside Nanochromis transvestitus and Nanochromis wickleri, distinguishing it from the four rheophilic congeners (Nanochromis consortus, Nanochromis minor, Nanochromis parilus, Nanochromis splendens) that are specialists of fast-flowing rapids. The Catalog of Fishes (Eschmeyer/CAS) is followed here as the authority for the valid name.
Morphology
This is a small cichlid — FishBase records a maximum of 2 in standard length for unsexed/male specimens, and Aquarium Glaser notes males reaching approximately 3 in total length in captivity. Like its congeners, the body is elongated and laterally compressed rather than the deep-chested build of substrate-brooding mbuna or Neotropical earth-eaters.
The diagnostic characters separating Nanochromis teugelsi from its relatives were established in the original description: it lacks a supraneural bone and lacks scales on the nape, cheek and chest, while possessing a fully scaled opercle. The upper lateral line is more elevated than in related species, running contiguous to the dorsal-fin base from approximately the sixth pored scale. These features separate it from Nanochromis dimidiatus, Nanochromis sabinae and Nanochromis squamiceps (which have scales on nape/cheek/chest), from Nanochromis minor, Nanochromis transvestitus, Nanochromis nudiceps, Nanochromis wickleri and Nanochromis splendens (which have an unscaled opercle), from Nanochromis consortus (by a shorter, shallower caudal peduncle), and from Nanochromis parilus (by fewer gill rakers on the first arch).
Coloration is striking for a fish of this size. The body ground colour runs from tan to pale grey, overlain by a series of dark vertical bars; the fins carry iridescent blue, purple and green highlights, and the upper lobe of the caudal fin typically shows a red stripe — a field mark shared with several Nanochromis but pronounced in teugelsi. The eyes are red-tinted. Sexual differences are pronounced: females develop a rounder body profile and, when ripe, display a vivid purple to pink flush on the abdomen that is absent or muted in males.
Habitat
Nanochromis teugelsi is an inhabitant of the middle Congo basin, from the Kwilu and Kasai drainages eastward through Lake Tumba and the main channel of the Congo River between the two. The type locality — the Kasai River at Bokoni village, Bandundu Province — exemplifies the soft, deeply tannin-stained waters that typify this part of the basin.
The waters of the Kasai system are characteristically low in dissolved salts: general hardness of 2–8 dH is documented for the genus in the region, and a pH in the range of 6.0–7.5 covers most wild-sample data, with some Lake Tumba water considerably more acidic (pH 4.5–5.5). Substrates are typically fine sand and silt, with abundant submerged wood, leaf litter and overhanging vegetation providing the shaded recesses that Nanochromis use as foraging and breeding sites. The species is classified as benthopelagic and tropical (FishBase), spending most of its time near the bottom and in structure rather than in open water.
Feeding
Nanochromis teugelsi is a carnivore-leaning omnivore, consistent with its FishBase trophic level of 3.2 ±0.4. In the wild it forages over sandy and silty bottoms, picking through leaf litter and detritus for small invertebrates — worms, crustaceans, insect larvae and similar soft-bodied prey.
In the aquarium the species accepts high-quality frozen and live foods readily: bloodworm, Daphnia, Artemia and micro-worm are all taken. Dried granular foods of appropriate size are accepted by acclimated fish, and a mixed diet with a plant-matter component (following genus-level omnivory recommendations) appears to improve long-term condition. Because wild fish encounter very low-nutrient blackwater, rich commercial diets should be given in modest quantities to avoid water-quality issues.
Mating
Like all Nanochromis, Nanochromis teugelsi is a monogamous, biparental cave-spawner. A bonded pair cooperates through territory selection, site preparation, spawning and the full rearing cycle — a reproductive organisation that the genus shares with many other small cichlids of the Congo basin but has refined around sheltered substrates rather than open pits or mouthbrooding.
Cavern selection is central to the pair's courtship dynamic: the female in particular is highly discriminating about the entrance diameter of a candidate cave, preferring openings barely wide enough to enter. Courtship intensifies as the pair clean the interior surfaces together. The female's belly flush deepens noticeably during pre-spawning, making sex determination straightforward even to casual observers at this stage. Field-specific mating observations are limited for this species, and the account here reflects the well-documented genus-level pattern.
Breeding
Spawning takes place inside the cave, with the female depositing a clutch of adhesive eggs on the cleaned interior walls or ceiling. Both parents guard the clutch through incubation, the female remaining close to the eggs while the male patrols the territory perimeter against intruders. Incubation is brief at tropical temperatures; the wrigglers are moved to pre-excavated sand pits, and by the free-swimming stage both parents are actively herding and defending the fry school.
Nanochromis teugelsi has been bred in captivity, though reports in the hobby remain relatively uncommon given the species' scarcity in trade. Breeding accounts note that cave dimensions matter: the female should be able to seal herself inside should the male turn aggressive, as is occasionally observed in Nanochromis pairs. Separating the parents once fry are free-swimming is advisable in smaller tanks. Soft, warm, low-germ water and a mature biological filter are considered prerequisites for successful spawning.
In the aquarium
Nanochromis teugelsi is a rare fish in the hobby, occasionally available from specialist Congo-cichlid importers and breeders, and worth seeking out for the keeper willing to replicate its soft-water blackwater environment. A dedicated species aquarium or a Congo community with Alestiid tetras (e.g. Phenacogrammus or Brycinus species) provides the most reliable context; cohabiting with other dwarf cichlids is possible but demands adequate space and sight-break density.
Water quality should be soft (≤8 dH), slightly acidic to neutral (pH 6.0–7.5), warm (72–79 °F / 72–79 °F), and very clean. Peat filtration or Indian almond leaves to acidify and colour the water are recommended by experienced keepers; the low-conductivity chemistry of the Kasai basin is the reference point. Fine sand substrate, multiple caves with narrow entrances, dense planting and wood or leaf-litter cover complete the setup. The species digs actively, so plants should be potted or well-anchored. Fed well and given appropriate conditions, Nanochromis teugelsi is a rewarding and visually distinctive dwarf cichlid — one that repays the extra attention its water requirements demand.
Conservation
Nanochromis teugelsi is assessed as Least Concern on the IUCN Red List (assessed 16 February 2009). Its range encompasses a substantial span of the middle Congo basin — the Kwilu and Kasai drainages, Lake Tumba, and the main channel — and there is no evidence of a range-wide decline at the time of assessment.
The broader Congo basin does face conservation pressures: artisanal and commercial fishing, deforestation of riparian zones, and expanding agriculture affect water clarity and chemistry across the Kasai system. However, the basin's enormous size and relative inaccessibility of many drainages have thus far buffered its fish communities from the kind of collapse seen in smaller, more fragmented river systems. The species' low profile in the aquarium trade means collection pressure is negligible. Monitoring remains limited in this part of Africa, and the 2009 assessment reflects the best information available at that time.