Taxonomy & naming
Tropheus sp. mpimbwe is an undescribed form complex — a recognizable geographic colour morph (or cluster of morphs) documented in the hobby and biotope literature (notably Konings' Cichlid Press titles and the photographic survey at tanganyika.si) but not yet given a formal scientific description. Tropheus is a small genus of stout, blunt-headed rock-grazers endemic to Lake Tanganyika, famous for fragmenting into well over a hundred allopatric colour races along the shoreline. Forms in this complex are referred to by their trade name until a revision formally treats them. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) remains the authority for the valid names in the genus.
Morphology
Like all Tropheus, this is a deep-bodied, blunt-snouted cichlid built for scraping rather than chasing, typically in the 4.5–6 in range. What distinguishes this complex from its relatives is coloration: each isolated population carries its own pattern of body colour and flank marking, which is precisely why aquarists track them by collection point. We deliberately avoid asserting a single "correct" colour description here — the reliable references are the photographs in Konings and at tanganyika.si, which document the living fish across the complex better than prose can.
Habitat
Tropheus is a lacustrine endemic of the rocky littoral, hugging boulder and cobble shoreline where it finds both grazing surface and refuge, and it is most abundant in shallow, well-lit water — roughly the upper few metres, and as a genus generally within the top ~66 ft. Populations of this complex are recorded around Lake Tanganyika part of Lake Tanganyika. Sand flats and open water act as hard barriers, which is what keeps each rocky population genetically and visually distinct.
Feeding
This is a dedicated grazer of "aufwuchs," the dense biofilm of algae and associated micro-organisms coating Tanganyika's rocks. The fish spends most of the day rasping this mat from hard surfaces; small invertebrates are taken only incidentally with the algae. The diet is essentially herbivorous (trophic level ~2.0), and the long digestive tract that comes with it is the single most important thing to respect in captivity.
Mating
Tropheus are highly social yet fiercely intraspecifically aggressive, ranking among the more combative Tanganyikan cichlids. Individuals hold and defend feeding territories on the rock face, and courtship plays out on the rock surface, the male displaying to the female before spawning.
Breeding
It is a maternal mouthbrooder: after a rock-top courtship the female takes up her eggs and they are fertilized near the male's vent, after which she alone carries the developing eggs and larvae in her buccal cavity for roughly four weeks. Clutches are small — on the order of 5–20 large eggs — so the female releases a handful of well-developed fry rather than a cloud of tiny ones. There is no biparental care.
In the aquarium
This is not a beginner's fish. The cardinal rule is dietary: Tropheus are prone to "bloat," a frequently fatal gut inflammation linked to protein- or fat-rich food, so keepers feed spirulina- and vegetable-based foods and avoid mammalian proteins, bloodworms and tubifex entirely. They are kept in larger groups to diffuse aggression, in hard, alkaline water with strong filtration. Because each locality form is genetically distinct, responsible keepers never mix different Tropheus populations in one tank — doing so destroys the very provenance that makes these forms worth keeping.
Conservation
Undescribed forms are not individually assessed by the IUCN, and no single lake-wide threat applies. The real conservation concern is local: because a colour form like this is confined to a short, isolated stretch of shoreline, its population can be depleted in place by over-collection for the trade in a way the species as a whole is not. Buying captive-bred, provenance-labelled stock is the practical safeguard.