Taxonomy & naming
Steatocranus mpozoensis was described in 1976 by the American ichthyologists Tyson R. Roberts and Donald J. Stewart in their landmark monograph 'An ecological and systematic survey of fishes in the rapids of the lower Zaïre or Congo River' (Bulletin of the Museum of Comparative Zoology 147(6):239–317). The species account appears on page 297, illustrated on Plate 12 (figure c). The holotype, catalogued as MCZ 50586 in the Museum of Comparative Zoology at Harvard, was taken in the rapids of the Mpozo River at roughly 5°51′S, 13°31′E; a series of paratypes is held at the MCZ and the Natural History Museum, London. The genus Steatocranus was erected by George Albert Boulenger in 1899 for Steatocranus gibbiceps, and in their 1976 revision Roberts and Stewart synonymised Leptotilapia Pellegrin, 1928 and Gobiochromis Poll, 1939 into it, describing mpozoensis alongside glaber and ubanguiensis as new species. Within the genus, Roberts and Stewart noted that mpozoensis is one of the low-bodied, slender species, contrasting with the high-headed gibbiceps and casuarius; it is most similar to gibbiceps but distinguished by its narrow, relatively pointed snout, its dentition, and a higher gill-raker count. The genus sits in the African subfamily Pseudocrenilabrinae, and the Cichlid Room Companion places it in the tribe Steatocranini. A molecular study of the lower Congo radiation by Schwarzer and colleagues (2011) recovered mpozoensis within a clade of lower-Congo endemics together with Steatocranus glaber and forms allied to gibbiceps and tinanti, a group dated to roughly 3 to 4.5 million years old. The disjunct West African Steatocranus irvinei of the Volta has since been removed from Steatocranus into the genus Paragobiocichla (Weiss et al., 2019), leaving Steatocranus as a strictly Congo-basin lineage.
Morphology
This is a small cichlid. FishBase lists a maximum of 2 in standard length, drawn from the CLOFFA checklist, but museum material runs larger: in their meristic survey Weiss and colleagues (2019) record the largest specimen of Steatocranus cf. mpozoensis — a male from Boma — at 3.5 in SL (4.5 in total length), and a number of examined fish exceed 3 in SL, so 3–3.5 in SL is a more realistic ceiling for well-grown adults. The body is elongated and only moderately deep, the typical low-slung profile of a rheophilic Steatocranus rather than the swollen-headed look of the popular buffalohead, Steatocranus casuarius. In keeping with the genus, the head and nape are essentially scaleless, the squamation reduced, and the pelvic fins are rounded with a thickened, skin-covered leading spine — all features read as adaptations to clinging and manoeuvring in current. The snout is relatively narrow and pointed and the mouth subterminal, set for working over rock. Roberts and Stewart figured the dentition as part of their genus-wide comparison. Live colour is documented mostly from aquarium and field photographs rather than the original description: a muted grey-brown to olive ground, often with a paler underside and dark markings that can resolve into longitudinal lines or faint vertical bars depending on mood. As in other lionhead cichlids, dominant and breeding males tend to develop a heavier, more swollen nape and grow larger than females, but the sexes are otherwise similar and no strong colour dimorphism is recorded for this species.
Habitat
Steatocranus mpozoensis is a narrow-range endemic of the lower Congo (formerly lower Zaïre) River system in the far west of the Democratic Republic of the Congo. It is known from the Mpozo River — a small left-bank tributary that joins the Congo near Matadi — and from the main river in the Matadi and Boma regions, downstream of the Yalala cataract and not far from the head of the estuary. In the molecular survey of Schwarzer and colleagues (2011), it stands out as the single Steatocranus species found below Yalala, where the rapids give way to the lowest stretch of free-flowing river before tidewater. This is rheophilic habitat in the most extreme sense: the lower Congo carries an enormous discharge through a narrow, rocky channel, generating the planet's largest rapids, with depths exceeding 656 ft and current velocities of several metres per second in the main flow. The fish themselves live in the broken, rock-strewn margins and tributary rapids rather than the deep central torrent, in shallow water generally no more than a couple of metres deep where they can shelter among stones. Roberts and Stewart measured the chemistry of these waters during their 1973 collecting: mainstream rapids were warm, very high in dissolved oxygen, near-neutral in pH, and remarkably low in alkalinity — soft, mineral-poor water. Tributaries such as the Mpozo ran slightly cooler than the mainstream. Equatorial water temperatures in this reach sit broadly in the mid-20s Celsius.
Feeding
No gut-content study has been published specifically for Steatocranus mpozoensis, and FishBase carries no diet record beyond an estimated trophic level of about 3.2, which places it as a low-level omnivore leaning toward small animal prey. Its feeding ecology is best inferred from the genus and from its mouth structure. Steatocranus are benthic foragers of the rapids, working over and between rocks with a subterminal mouth to scrape and pick at the thin biofilm of algae, detritus, and the small invertebrates that live in the boundary layer of fast water — aquatic insect larvae, micro-crustaceans, and the like. Roberts and Stewart noted that the congener Steatocranus gibbiceps, the most abundant cichlid in their rapids collections, was a specialist that swallowed gastropod snails whole; mpozoensis, with its different dentition and narrower snout, is not described as such a mollusc-feeder and is better regarded as a generalist gleaner of the rock surface. In the aquarium the species behaves as an unfussy omnivore, taking prepared, frozen, and live foods readily. Within its rapids community it occupies the crowded benthic guild alongside other Steatocranus, the dwarf Nanochromis, the rheophilic Lamprologus, and the highly specialised Teleogramma, all of them partitioning the rocky substrate of one of the most demanding freshwater habitats on earth.
Mating
Reproductive behaviour has not been described from the wild for Steatocranus mpozoensis, but its mode is documented at the genus level and is consistent across the lionhead cichlids: they are monogamous, pair-bonding fish that hold a territory centred on a rocky crevice or cavity. FishBase explicitly characterises the species as 'pair-bonding and cave spawning.' By analogy with the much better studied Steatocranus casuarius and Steatocranus tinanti, pairs form a durable bond and both partners cooperate in defending a small territory around the chosen shelter. Because the fish have a reduced swim bladder and live pressed to the substrate, courtship and territorial display play out as bottom-bound posturing, lateral spreading, and jaw-to-jaw confrontation among males rather than open-water chasing. Territoriality is concentrated around the spawning cavity and is at its most intense once a pair has committed to a site; outside breeding these are comparatively retiring, rock-hugging fish. Males average larger than females and a dominant male may develop a swollen nape, the usual signal of breeding condition in the genus.
Breeding
Steatocranus mpozoensis has not, as far as the published record shows, been bred and documented in detail, but it is unambiguously a biparental cave spawner — the reproductive strategy shared by every Steatocranus whose breeding is known. In this mode the female deposits a modest clutch of adhesive eggs on the ceiling or wall of an enclosed cavity among the rocks, and the pair tends them together: the female concentrates on cleaning and fanning the eggs while the male guards the approaches to the cave. Clutches in the genus are small by cichlid standards — congeners such as Steatocranus casuarius typically lay on the order of 20 to 60 large eggs — reflecting the trade-off of cave-brooding fish toward fewer, well-protected young. The eggs hatch into wrigglers that are kept in the cavity, and once free-swimming the fry are shepherded by both parents and bolt back to shelter at any disturbance, a behaviour suited to a turbulent rock habitat where open water is dangerous. Given the genus's biology, spawning is likely tied to favourable, warm, well-oxygenated conditions rather than to a strong seasonal flood cue. All of these specifics are extrapolated from close relatives; the actual fecundity, egg size, and developmental timing of mpozoensis itself remain undocumented and would be worth recording from aquarium stock.
In the aquarium
Steatocranus mpozoensis is essentially never seen in the aquarium trade. The genus is represented in the hobby almost entirely by Steatocranus casuarius (the buffalohead or lionhead cichlid) and to a lesser extent Steatocranus tinanti and a handful of undescribed 'Steatocranus sp.' forms; mpozoensis, a narrow-range fish from a remote and poorly collected reach of the lower Congo, has only occasionally turned up among mixed wild imports, and is not commercially distributed. Anyone who did keep it should treat it exactly as an advanced rheophilic Congo cichlid, because its requirements are dictated by the rapids it comes from. That means a tank built around moving, highly oxygenated water: strong filtration and added flow (a powerhead or two), excellent surface agitation, and immaculate water quality, since rapids fish tolerate dissolved waste poorly. A footprint of around 31.5 in or more for a pair is sensible — the genus is territorial and benefits from floor space and broken sightlines. Aquascaping should be rock-dominated, with piles of smooth stones and slate arranged to create the caves and crevices these fish use both as refuges and as spawning sites; a sand or fine-gravel base suits their bottom-crawling habit. Because of the reduced swim bladder, Steatocranus mpozoensis will not hover in mid-water but will hop, perch, and dart across the hardscape, so the layout should give it surfaces to occupy at every level. Water should mirror the wild: warm (roughly the mid-20s Celsius), soft and low in mineral content, and near neutral — the lower Congo runs near pH 7 with very low alkalinity, so anything from mildly acidic to mildly alkaline (around pH 6.5–8.0) is acceptable provided it is stable and well oxygenated. Feeding is straightforward: a varied omnivore diet of quality sinking foods, frozen invertebrates, and the occasional vegetable matter. Tankmates, if any, should be other robust, current-loving Congo species rather than placid community fish, and conspecific aggression around breeding sites should be expected. This is a specialist's fish that would be kept for its biology and rarity rather than its colour.
Conservation
The IUCN Red List assesses Steatocranus mpozoensis as Data Deficient (DD), in an assessment by T. Moelants dated 16 February 2009. The Data Deficient category reflects exactly the situation the literature describes: a species known from very few collections in a small area, with too little information on its population, range limits, and ecology to judge its extinction risk. That narrow, single-region distribution — the Mpozo River and the lower Congo around Matadi and Boma — is itself a source of concern, because narrow-range endemics of the lower Congo are inherently vulnerable to localised disturbance. The lower Congo rapids are a globally exceptional freshwater ecosystem and a recognised centre of cichlid endemism, but they sit immediately downstream of the Inga hydropower complex, and the long-discussed Grand Inga scheme and associated development would alter flow, sediment, and connectivity in precisely the rapids habitat these fish depend on. Pollution and habitat modification around the busy river port of Matadi add further local pressure. None of this has been quantified for mpozoensis specifically, which is the heart of its Data Deficient listing; better field survey of the Mpozo and the reach below Yalala is the obvious priority before any firmer conservation judgement can be made.