Taxonomy & naming
Orthochromis kalungwishiensis was described in 1994 by Peter Humphry Greenwood and Sven O. Kullander, who originally placed it in the genus Schwetzochromis. It was reassigned to Orthochromis in the 1998 revision of rheophilic East African haplochromines by De Vos and Seegers, and Eschmeyer's Catalog of Fishes lists it as valid as Orthochromis kalungwishiensis (Greenwood & Kullander, 1994), with the parentheses signalling that combination change. The genus Orthochromis was erected by Greenwood in 1954 for small, current-loving haplochromine cichlids of African river rapids; the name combines Greek 'orthos' (straight) and 'chromis' (a cichlid), in reference to the straight body profile of these stream fishes. As now applied, Orthochromis is a loose grouping of rheophilic haplochromine lineages across the Malagarasi, Lufubu, other Lake Tanganyika–region rivers and the upper Congo (Lualaba, Luapula, Lufira and associated) drainages rather than a single natural clade. The specific epithet is a toponym, formed from the Kalungwishi River — the species' type locality and only known home — with the Latin suffix '-ensis' ('belonging to').
Morphology
Orthochromis kalungwishiensis is a small cichlid, reaching about 4 in standard length according to FishBase — among the larger of the rheophilic Orthochromis but still a modest fish. It has the genus's typical rheophilic form: an elongate, low and only moderately compressed body suited to holding position in current, with the straight dorsal profile that gives the genus its name. Like the other current-dwelling Orthochromis it shows muted brown-grey colouration broken by darker vertical bars on the flanks, the cryptic livery of a fish that lives among rocks in moving water. Unlike a few of its congeners (such as Orthochromis gecki and Orthochromis indermauri), it does not carry the distinctive orange anal-fin eggspots; the species was diagnosed by Greenwood and Kullander on a combination of meristic and morphometric characters within the rheophilic haplochromine assemblage. Detailed notes on sexual dimorphism are limited in the literature.
Habitat
The species is endemic to the Kalungwishi River, a major tributary that drains into Lake Mweru on the Zambia–DR Congo border, within the upper Congo basin; the type locality is at Kundabwika Falls, immediately above the rapids, in Northern Province, Zambia (around 9°13′S, 29°18′E). This is classic rheophilic habitat — clear, fast-flowing water over rocky substrate near falls and rapids, with the fish reported from near the shore down to depths of around two metres over rock. As a benthic rheophile it holds station among the stones in the current rather than ranging into still or open water, and on current knowledge it does not enter Lake Mweru itself but remains a creature of the flowing river. Its restriction to a single river system is the defining feature of its distribution.
Feeding
No dedicated dietary study has been published for Orthochromis kalungwishiensis. By the ecology of the genus it is best understood as a benthic grazer-invertivore of fast water, taking aufwuchs — the film of algae and associated micro-invertebrates coating the stones of sunlit riffles — together with aquatic insect larvae and other small bottom invertebrates dislodged in the current. The low body and ventrally-oriented mouth characteristic of rheophilic Orthochromis suit a fish that rasps and picks at rock surfaces while bracing against flow. Any finer account of its diet would, for now, be inferred from the genus rather than directly observed.
Mating
Courtship has not been described in detail for kalungwishiensis, but rheophilic Orthochromis are maternal mouthbrooders and the species is expected to follow the standard haplochromine pattern. A male holds and defends a small territory among the rocks, displays to passing females, and leads a receptive female over a chosen spawning site; the female takes the eggs into her mouth, where fertilisation is completed. In species that carry anal-fin eggspots these act as decoys during fertilisation, but kalungwishiensis lacks conspicuous eggspots, so any analogous signalling would rest on body coloration and display rather than fin ocelli. The specifics for this species in its rapids habitat are inferred from the genus rather than documented.
Breeding
There is no published account of clutch size or fry development specific to Orthochromis kalungwishiensis. By the consistent biology of the rheophilic Orthochromis it is a maternal mouthbrooder: the female incubates the fertilised eggs and then the larvae in her buccal cavity for some weeks before releasing free-swimming fry, which may shelter back in her mouth when threatened, with the male giving no parental care. In a river haplochromine of this size, broods are likely modest — on the order of tens of relatively large eggs — the small clutch offset by the protection oral incubation provides in fast, predator-rich water. As with much of this fish's biology, the figures here are extrapolated from the genus rather than recorded for the species.
In the aquarium
Orthochromis kalungwishiensis is not a fixture of the aquarium hobby. It is a single-river endemic from a remote part of the upper Congo basin and is essentially absent from the ornamental trade, so there is no established body of keeping or breeding experience for it; even among the rheophilic Orthochromis only a few species reach specialist tanks.
Any husbandry notes are extrapolated from its close relatives and its habitat. Rheophilic river cichlids of this kind need clean, hard, alkaline, very well-oxygenated water kept in strong motion, a rocky and rubble substrate with crevices and current-breaks, and stable warm temperatures. Powerheads or a river-tank flow manifold, vigorous filtration and frequent water changes are the essentials; soft, still, organically loaded water is the opposite of what they tolerate. They are small, busy, substrate-bound fish best kept as a group in a species setup or with other robust rheophiles. The honest summary is that this is a fish for the committed river-cichlid keeper, and one most readers will encounter on the page rather than in a tank.
Conservation
Orthochromis kalungwishiensis has not been assessed by the IUCN Red List and carries no formal conservation status. Its conservation interest is straightforward: it is a single-river endemic, known only from the Kalungwishi system, which makes its entire known population dependent on one river and its falls and rapids. Rheophiles of this kind are highly sensitive to anything that ponds, silts or de-oxygenates flowing water — hydropower and dam development, water abstraction, mining-related sedimentation and catchment deforestation among the regional pressures, and the Kalungwishi has itself been a focus of hydropower interest. There is also a recognised regional threat to upper-Congo cichlid diversity from hybridisation and competition where non-native species are introduced. No CITES listing or fishery interest applies, but the narrow range and demanding fast-water niche make the species a reasonable candidate for future conservation attention.