Taxonomy & naming
Aulonocara sp. "Nyassae Mumbo" is a provisional, informal name for a Mumbo Island population that Lake Malawi field workers place close to Aulonocara nyassae Regan, 1922 — the genus's type species — without asserting that the two are conspecific. It is treated here in the convention used by Ad Konings and others, who tag distinct local populations with the genus, "sp.", and a working epithet (here combining the affinity, "nyassae", with the locality, "Mumbo") precisely to flag a form that is not formally described in its own right. The affinity to Aulonocara nyassae is stated honestly as a similarity in colour and morphology, not a determination: the Mumbo form may ultimately prove a colour population of Aulonocara nyassae, a distinct undescribed species, or a member of a broader complex around that name — the matter is unresolved. Crucially, the validly described Aulonocara nyassae is a real, named species with its own authority and history; this quoted "Nyassae Mumbo" form is a separate, informal designation and carries no such standing. With no published description of the Mumbo form there is no holotype, no fixed type locality, no authority, and no year for it; any FishBase number or IUCN status attached to this informal name would be unfounded.
The designation "Nyassae Mumbo" is a hobby/field tag with no nomenclatural standing of its own. It is not italicised in formal usage, takes no authority and no date, and would gain neither unless a worker publishes a description fixing a type and diagnosis for the Mumbo form under the International Code of Zoological Nomenclature. The genus Aulonocara Regan, 1922 is well founded, diagnosed by the conspicuously enlarged cephalic lateral-line canals and sensory pores shared across the peacock group, and Aulonocara nyassae Regan, 1922 is its type species; long-standing confusion has surrounded the application of the nyassae name to various yellow peacocks across the lake, which is part of why distinct regional populations such as the Mumbo form are flagged informally pending revision. The responsible course, taken here, is to use the quoted informal name, withhold any invented author or year for it, state the affinity to Aulonocara nyassae honestly as provisional, and describe what is observed rather than assert that the Mumbo form is the same species or that it constitutes a new one.
Morphology
Aulonocara sp. "Nyassae Mumbo" is a peacock of typical genus build — a moderately deep, laterally compressed haplochromine body, mature males running larger than females — bearing the diagnostic head apparatus of the genus: lateral-line canals widened into a system of conspicuously enlarged sensory pores used to detect buried prey. Sexual dichromatism is marked, as across the peacock radiation: dominant territorial males carry nuptial colour in the yellow-to-blue register characteristic of the nyassae-allied peacocks, while females and non-territorial males are plainer, smaller and cryptically marked over silvery-brown. Precise meristic and morphometric figures for the Mumbo form are not available because no formal description of it has been published, so a fixed maximum length or fin-ray count should not be cited as established for this informal name. What is reliable is qualitative: a yellow-and-blue peacock of the nyassae grade from Mumbo, with the genus's enlarged cephalic pores and the strong male/female colour split the group is known for.
Habitat
Aulonocara sp. "Nyassae Mumbo" is reported from the Mumbo Island area in the south-western arm of Lake Malawi, a region of rocky islands grading into sandy floor that hosts a rich peacock community. The form occupies the classic Aulonocara intermediate zone — scattered rocks and rubble standing on sand rather than continuous rock or pure sand — at the moderate depths typical of the rock-and-sand peacocks, broadly the upper habitat band on the order of several metres down to around 49–82 ft. The water is Lake Malawi's warm, hard, strongly alkaline medium: temperatures around 75–82 °F, pH in the alkaline 7.7–8.6 range, and high carbonate hardness. Because the name is informal and no field assessment has formally delimited the Mumbo form's distribution, the locality given here marks the island region with which the form is associated in field and hobby usage, not a formally established range.
Feeding
Like all peacocks, Aulonocara sp. "Nyassae Mumbo" is a sand-sifting micro-invertivore that locates prey through the ampullary and enlarged lateral-line pores of the head. It hovers just above the substrate between and around the rocks of its habitat, holding station while the cephalic sensory system registers the faint movements of invertebrates buried in the sand; on detecting prey it darts down, takes a mouthful of sediment, sifts out edible items, and expels the spent grains through the gills and mouth. This benthic strategy ties the fish to clean, invertebrate-rich sand rather than to algae grazing. In captivity the implication mirrors that of its described relatives: a fine sand bed that permits natural sifting (coarse gravel inhibits the behaviour and can abrade the gills), plus a varied diet of fine prepared foods and small live or frozen invertebrates such as chironomid larvae and brine shrimp.
Mating
As a Lake Malawi haplochromine, Aulonocara sp. "Nyassae Mumbo" follows the polygynous, lek-like social pattern of the peacock radiation, with no pair bond. Males in nuptial colour establish and defend small territories on the sand or at the base of rocks, each typically centred on an excavated pit or sheltered spot beneath rubble; females are non-territorial and move singly or in loose groups, visiting displaying males. Courtship is brief and conventional for the genus: a ripe female approaches a colour-flashing male at his site and spawning follows directly. Because dominant males of these rock-and-sand peacocks hold colour for extended periods, the lek is effectively active across much of the year. In the aquarium the practical corollary is the group standard — a single male with several females avoids the relentless aggression that surplus males direct at rivals and at similarly patterned tankmates.
Breeding
Aulonocara sp. "Nyassae Mumbo" is, like every member of the genus, a maternal (ovophilous) mouthbrooder. After courtship draws a willing female to the male's spawning site, she lays a small batch of eggs and immediately takes them into her mouth; drawn to the egg-spot markings on the male's anal fin, she mouths at these and takes in milt that fertilises the clutch already held in her buccal cavity. Aulonocara clutches are modest — typically a few dozen eggs in this size class — and the female broods them in her mouth for roughly three to four weeks, feeding little or not at all, before releasing free-swimming fry; she then provides no further care, and there is no biparental investment. The fry can take brine shrimp nauplii once any remaining yolk is absorbed. Like its relatives, the form is expected to breed readily in captivity, which makes maintaining it as a clean, unhybridised line — and not crossing it with Aulonocara nyassae or other yellow peacocks — important for keepers who value its identity.
In the aquarium
Aulonocara sp. "Nyassae Mumbo" is kept and traded as a regional yellow peacock, and — as with all informal forms allied to a confused described species — the single most important husbandry caution is provenance. Because the nyassae name has long been applied loosely across the lake and the rock-and-sand peacocks cross readily, fish sold under this Mumbo tag vary in origin and purity. A keeper who wants the form as a distinct entity should buy from a specialist breeder who keeps records and does not mix related peacocks, and should avoid the casual all-male peacock tank if the goal is ever to breed true.
A single colony of one male with three or four females is the natural and recommended arrangement. Males in permanent nuptial colour are perpetually ready to spawn and will harass unreceptive females in a bare tank, so provide a footprint of at least 47 in with generous open swimming space, a fine sand bed at least 2 in deep to support sifting behaviour, and a background of stacked rock giving broken sightlines and refuges. Dense planting is neither required nor natural.
Water chemistry should mirror Lake Malawi's upper column: temperature about 75–82 °F, pH 7.7–8.6, and moderate-to-hard general hardness, with soft or acidic water avoided. Weekly partial water changes of 20–30 % matter because accumulated nitrate stresses Malawi cichlids even when ammonia and nitrite read zero. Diet is the standard peacock regime — a quality cichlid pellet or flake staple plus frozen or live chironomid larvae, brine shrimp and daphnia fed over the sand to encourage natural sifting — while high-fat foods, which predispose Malawi cichlids to bloat, are best avoided; spirulina-enriched foods are a sensible regular addition. Breeding follows the standard peacock routine and usually needs no intervention beyond optionally moving a clearly carrying female to a holding tank.
Conservation
No IUCN Red List assessment exists for Aulonocara sp. "Nyassae Mumbo", and none can, because the Mumbo form has not been formally described — the Red List evaluates validly named taxa. Its conservation standing is therefore unknown, and no status, category, or assessment year should be attributed to it. (The validly named Aulonocara nyassae to which it is allied is a separate matter and should not have its status borrowed for this informal form.) Contextually, the rock-and-sand yellow peacocks of Lake Malawi's south-western islands are exposed as a group to ornamental-trade collection pressure, and several validly named peacocks with narrow ranges have drawn conservation concern; whether the Mumbo form is a distinct narrowly distributed population at similar risk or part of a wider-ranging complex cannot be resolved until the taxonomy is. The honest position is that this is an unevaluated, informally named form whose very identity relative to Aulonocara nyassae is unsettled; responsible keepers should favour captive-bred, record-kept stock.