Taxonomy & naming
Cynotilapia sp. "Ndumbi" has never been formally described. It has no describing author, no publication date, and no entry under a validated name in Eschmeyer's Catalog of Fishes. The form was first identified in the scientific literature by Ribbink and coworkers during their landmark early-1980s rocky-shore survey of Lake Malawi, which catalogued dozens of geographically restricted mbuna colour forms by field name rather than formal description — "Ndumbi", after Ndumbi Rocks near Likoma Island, is one of these. This database also records the form from Linganjala Reef, a further locality in the same general south-central area of the lake. Cynotilapia (Regan, 1922) is a compact genus of small mbuna defined by unicuspid, dog-like teeth, unusual among mbuna, most of which carry bicuspid or tricuspid teeth suited to scraping algal turf — a dental difference that underpins a genus radiated into an unusually large number of narrow-range colour forms, of which this is one of the more distinctive, being almost entirely black.
Morphology
Ribbink and coworkers recorded the coloration of C. sp. "Ndumbi" as almost entirely black, a striking departure from the blue-based, black-barred pattern typical of most Cynotilapia forms documented around the lake. Beyond that colour account, no detailed morphometric study has been published for this form. It should carry the genus's diagnostic single row of unicuspid, canine-like teeth in each jaw and the compact, moderately elongate body typical of small Cynotilapia. Genus-typical size runs to roughly 3–3.5 in total length, with males somewhat larger than females; the near-black coloration is presumed to intensify in mature, dominant males, following the general pattern of breeding dichromatism in the genus, though this has not been confirmed specifically for this form.
Habitat
The type locality, Ndumbi Rocks, lies near Likoma Island in the south-central part of Lake Malawi; this database also records the form at Linganjala Reef, a further site in the same general area. Unusually for the genus, Ribbink's survey recorded C. sp. "Ndumbi" living in secluded caves in shallow water rather than foraging openly across exposed rock and sand, a more retiring lifestyle than the typical Cynotilapia pattern of picking food from open reef surfaces. Water chemistry in this part of the lake follows Lake Malawi's standard rocky-shore profile — warm, hard, and strongly alkaline.
Feeding
Cynotilapia's diagnostic unicuspid "dog-tooth" dentition sets its feeding apart from most other mbuna, which use closely packed bicuspid or tricuspid teeth to scrape tightly bound algal turf directly off rock. Cynotilapia species instead pick loose diatoms, filamentous algae, and fine organic detritus from rock and sand. Given its documented preference for secluded caves rather than open reef, "Ndumbi" may forage more within sheltered crevice microhabitats than the genus-typical pattern of picking across exposed rock, but no dedicated dietary study has confirmed this, and the account here otherwise follows genus-wide expectations.
Mating
No detailed courtship account exists specifically for "Ndumbi", though its cave-dwelling habit suggests territories may be built around a defended crevice rather than open rock, a variation on the standard Cynotilapia pattern of mature males holding a small patch of reef and displaying to passing females in breeding colour. The genus generally shows lower intraspecific aggression and smaller, less fiercely contested territories than larger mbuna genera such as Maylandia or Petrotilapia. Courtship is expected to follow the typical haplochromine sequence, with a receptive female drawn into a displaying male's territory to spawn.
Breeding
As in every Lake Malawi haplochromine, reproduction is by maternal mouthbrooding. The female takes fertilised eggs into her mouth immediately after spawning and carries them, without feeding normally, until the fry are large enough to be released as free-swimming young; the male provides no further care. Clutch sizes in small Cynotilapia species are modest, typically a few dozen eggs, and the brooding period runs roughly three to four weeks in the genus generally. A secluded cave environment may offer the brooding female extra shelter compared with the open reef most mbuna use, though this has not been directly studied for this form.
In the aquarium
"Ndumbi" is a rare fish in the trade, consistent with Ribbink's original description of it as uncommon even at its own type locality. Where it is kept, it should be provided with unusually generous cave and crevice structure compared with a typical Cynotilapia setup, reflecting its documented preference for secluded, shaded refuges over open rockwork. Otherwise, standard small-mbuna husbandry applies: a sand substrate, water matching Lake Malawi's rocky zone — hard, strongly alkaline (pH roughly 7.7–8.6), and warm (75–82 °F) — and a tank of at least 39.5–47 in footprint for a group of one male to several females. Diet should lean vegetable, a spirulina-based flake or pellet supplemented sparingly with small invertebrates, avoiding fatty, protein-heavy foods because of the elevated Malawi-bloat risk common to the genus.
Conservation
"Ndumbi" has not been evaluated by the IUCN and, as an undescribed form with no formal scientific name, carries no Red List status of any category. Ribbink's original account already flagged it as rare at its type locality, and its documented range — Ndumbi Rocks and Linganjala Reef — is narrow even by the standards of Lake Malawi's fine-grained mbuna endemism. A cave-dwelling, low-density population confined to a small stretch of shoreline is inherently more exposed to localised disturbance than a widespread, open-reef species, even where no specific modern threat has been documented.