Taxonomy & naming
Nanochromis wickleri was described in 2006 by Ulrich K. Schliewen of the Bavarian State Collection of Zoology and Melanie L. J. Stiassny of the American Museum of Natural History, in the journal Zootaxa (1169: 33–46). The holotype (ZSM 29695) and its paratypes were collected at Lake Mai Ndombe close to the town of Inongo, just south of the harbour, in what was then Bandundu Province of the Democratic Republic of the Congo. The genus Nanochromis itself dates to Pellegrin (1904), erected as a replacement name for Boulenger's preoccupied Pseudoplesiops, with Nanochromis nudiceps as type species; it belongs to the chromidotilapiine cichlids of the subfamily Pseudocrenilabrinae, a West and Central African lineage of small, biparental cave spawners. Over the decades the genus has repeatedly shed species to other genera — Greenwood split off Limbochromis and Parananochromis in 1987, and in 2007 Stiassny and Schliewen removed several softer-water forms to the new genus Congochromis — leaving a tight cluster of true Nanochromis confined to the Cuvette Centrale and the rapids of the lower Congo. Within that residue the authors tentatively assigned wickleri to a morphologically diagnosable subclade they named the 'nudiceps group', while stressing that a comprehensive phylogenetic analysis would be needed to confirm the placement. No junior synonyms exist; the species has been recognized as valid since its description, and a subsequent molecular study (Schwarzer et al. 2011) recovered the two Mai Ndombe lake species, wickleri and Nanochromis transvestitus, as having diverged from one another several million years ago, consistent with the lake's status as a long-isolated lacustrine refuge.
Morphology
At a maximum recorded length of about 3 in standard length, Nanochromis wickleri is one of the larger members of its genus and, unusually, a notably deep-bodied one — most Nanochromis are very slender for their length. The original description diagnoses it by several features that set it apart from every congener. The most striking is the soft dorsal fin, which carries an elevated count of 10–11 soft rays where other Nanochromis have only 5–8; the full dorsal formula runs to 16–17 spines. In mature fish the second and third dorsal-fin spines also extend into strongly produced membranous 'lappets', trailing flaps of fin membrane that no other species in the genus develops. The anal fin bears three spines and eight soft rays, and the species has 28 vertebrae. The snout is long, with a steeply inclined, strongly convex upper profile and an almost straight lower one; the cheek and nape are nearly naked of scales, and the upper lateral line runs right against the base of the dorsal fin. The caudal fin is longer than it is deep and subacuminate, its central rays the longest. Internally the lower pharyngeal jaw is extremely gracile, with narrow horns, a short blunt keel, and only a sparse covering of fine, weakly bicuspid teeth — the dentition of a fish that takes small, soft prey rather than crushing hard shells. As in the rest of the genus, the sexes differ: Nanochromis show pronounced sexual dimorphism in which females carry conspicuously rounded, often reddish or violet bellies in breeding condition while males tend to grow larger and bear longer, more produced fins.
Habitat
Nanochromis wickleri is endemic to Lake Mai Ndombe (formerly Lake Leopold II), a vast, shallow blackwater lake occupying the lowest interior point of the Cuvette Centrale, the saucer-shaped depression at the centre of the Congo basin. The lake is large — roughly 84 mi long and up to 34 mi wide, covering some 2,186 mi² — but extraordinarily shallow, averaging only about 10 ft deep, and its water is stained dark as strong tea by humic acids leached from the surrounding swamp forests. It is among the most acidic large lakes on Earth: pH readings around the lake and its flooded margins typically run between 4.0 and 5.5, the water is very soft (often too dilute to register meaningful hardness), and equatorial temperatures stay warm and constant year-round, in the mid-to-upper 20s °C. The type series of wickleri came from a sandy beach interspersed with flat laterite terraces at depths of only 3–7 ft; the species is reported to keep to such firm-bottomed, rocky or lateritic stretches rather than the soft mud of the open lake. It is one of just two Nanochromis in the lake — the other being the famous reversed-dichromatism dwarf Nanochromis transvestitus — and both are sedentary lake-dwellers, far less adapted to current than the rheophilic Nanochromis of the lower Congo rapids. Mai Ndombe is a remnant of a far larger interior lake that once filled the Cuvette Centrale, and its long isolation makes it a hotspot of localized endemism: the cichlids Hemichromis cerasogaster and Nanochromis transvestitus are found nowhere else, and wickleri belongs to this same restricted lacustrine fauna. The lake remains poorly surveyed, so the species' true range within and around it is incompletely known.
Feeding
No direct dietary study of Nanochromis wickleri has been published — the lake is too lightly sampled and the species too recently described for gut-content work. Its anatomy and its membership in the genus, however, point clearly to a benthic micro-omnivore. The lower pharyngeal jaw is delicate, with sparse, fine, weakly bicuspid teeth rather than the robust molars of a mollusc-crusher, indicating a diet of small, soft items. FishBase estimates a trophic level near 3.3. Like other Nanochromis, it is a bottom-oriented forager that works sand and hard substrate for small invertebrates, larvae, crustaceans, and organic detritus, and its diet in nature almost certainly includes a substantial vegetable and aufwuchs component — the genus as a whole is regarded as omnivorous and requiring roughage. In the blackwater economy of Mai Ndombe, where the open water is nutrient-poor and much of the food base derives from terrestrial input and decomposing leaf litter washed in during the floods, a small generalist that grazes and sifts the firmer substrates is well placed. It is of no interest to fisheries.
Mating
The reproductive behaviour of Nanochromis wickleri has not been documented directly, but the genus Nanochromis follows a consistent and well-studied pattern that almost certainly applies. These are cave-spawning dwarf cichlids that form monogamous male–female pairs, and they are marked by strong sexual dimorphism in which the female, not the male, advertises readiness — swelling a brightly coloured belly and presenting it to her partner during courtship. Pair bonds can be durable or may dissolve after a single spawning. Both sexes are highly territorial and frequently aggressive toward their own kind, particularly in the confines of a small habitat; an unreceptive or mismatched fish, usually the weaker of a pair, may be harried relentlessly. A ripe female selects and prepares a secluded cavity, often one with an entrance barely wide enough to admit her, and it is the establishment and defence of this nest cavity that organizes the pair's territory. In its near relative Nanochromis transvestitus, which shares Lake Mai Ndombe, the dimorphism is famously reversed — the female is the gaudier sex — and that lake population has become a textbook example of the unusual breeding systems this genus can evolve.
Breeding
Breeding of Nanochromis wickleri has not been reported from the wild or, in any detailed published account, from aquaria, so its specifics are inferred from the strongly conserved biology of the genus. All known Nanochromis are biparental cave spawners. The female deposits her eggs on the ceiling or wall of a sheltered cavity — in nature a crevice among rock or laterite, in captivity readily a small cave or pot — and tends the clutch and the larvae inside while the male patrols and defends a wider perimeter around the entrance. Females commonly seal themselves into the chamber by pushing substrate across the opening, an alarming but normal behaviour. Clutch sizes in the genus are modest, on the order of a few dozen to perhaps a hundred or so eggs (genus-typical figure, not measured for wickleri). After the fry become free-swimming the female leads the school through the territory, often joined by the male in guarding them, and the parents continue to shepherd the young for several weeks before interest wanes. Spawning in Nanochromis is generally triggered by good condition and stable, very soft, acidic water rather than by any dramatic seasonal cue, though in Mai Ndombe the annual flood pulse — which brings oxygenated, food-rich water into the inundated margins — is the natural season of plenty for breeding fishes across the lake.
In the aquarium
Nanochromis wickleri is not, in practice, an aquarium fish: it is rarely if ever collected for the trade, its remote and barely-sampled lake sees almost no ornamental fishing, and there is no body of hobbyist experience specific to the species. Anyone who did obtain it should treat it as a demanding blackwater dwarf and extrapolate from its better-known congeners, above all the lake-mate Nanochromis transvestitus, which has a reputation as a challenging fish recommended only for experienced keepers.
The defining requirement is water chemistry. Mai Ndombe is one of the softest, most acidic large lakes anywhere, with a pH near 4.0–4.5 and hardness so low it is effectively unmeasurable. To keep this species in health one would need genuinely soft, acidic, tannin-stained water — reverse-osmosis water re-mineralized only minimally, peat or leaf-litter (Indian almond, alder) to lower pH and supply humic acids, and a target in the region of pH 4.5–5.5 with hardness no greater than about 2 dGH. Temperature should sit in the warm, stable equatorial band of roughly 75–82 °F. Bright lighting is wrong for a fish from water so dark you cannot see your hand at a foot's depth; subdued light, ideally with floating plants, suits it.
A pair needs a modest but well-structured tank. Fine sand is the correct substrate, as the fish dig; the layout should combine open foraging areas with dense cover — rockwork, driftwood, plant thickets — and several spawning caves with small, dark entrances. The single most important husbandry point inherited from the genus is intraspecific aggression: adults can be ferociously intolerant of one another in a small space, and a mismatched pair often ends with the weaker fish killed. Plentiful broken sightlines and multiple refuges are essential, and forced pairings are a project for experienced keepers only. Feeding is straightforward in principle — these are omnivores that take sinking pellets, frozen and live foods such as brine shrimp, daphnia and mosquito larvae, and need vegetable matter and roughage rather than an all-meat diet. Tankmates, if any, should be small, peaceful soft-water species that tolerate the same acidic conditions; the chemistry alone rules out most community fish. In short: a specialist's fish, kept the way one keeps Nanochromis transvestitus, and almost never seen.
Conservation
Nanochromis wickleri has not been evaluated by the IUCN Red List (status: Not Evaluated as of the 2025 Red List version), and it carries no CITES or CMS listing. That gap reflects how little is known about the species rather than any judgement of security. It is a narrow-range endemic confined to a single lake, which is intrinsically a vulnerable profile, but Lake Mai Ndombe is large, remote, lightly fished for ornamentals, and lies partly within a region that includes the southwest edge of Salonga National Park, so there is no evidence of an immediate population-level threat. The wider context is worth noting: Mai Ndombe is a blackwater–peatland system of global significance, fringed by some of the largest tropical peat deposits on the planet, and the lake and its swamp forests are increasingly studied as a major natural carbon store now beginning to outgas ancient carbon. Pressures on the Congo basin generally — deforestation, expanding settlement, hydrological change, and disturbance of the peat swamps — form the backdrop against which the long-term prospects of this and the lake's other endemics should be read. For now the honest assessment is that the species is simply too poorly known to assess, and a proper survey of Mai Ndombe's fish fauna is overdue.