Taxonomy & naming
Tylochromis robertsi was described by Melanie L. J. Stiassny in 1989 as part of her monographic revision of the genus, 'A taxonomic revision of the African genus Tylochromis (Labroidei, Cichlidae); with notes on the anatomy and relationships of the group' (Annales du Musée Royal de l'Afrique Centrale, Série Sciences Zoologiques, vol. 258). The holotype (MRAC 182224) was collected at Gangala na Bodio on the Dungu River, a headwater of the Uele system in the northeastern Democratic Republic of the Congo, and is held at the Royal Museum for Central Africa in Tervuren; an extensive paratype series is distributed among the AMNH, BMNH, IRSNB, MCZ and MRAC. The name has not been synonymised since and remains valid. Tylochromis itself was erected by Charles Tate Regan in 1920 (type species Paratilapia jentinki Steindachner, 1894) and is the sole genus of the tribe Tylochromini, a lineage that branches near the base of the African cichlid radiation (subfamily Pseudocrenilabrinae). Stiassny's revision recognised on the order of fifteen valid species and treated the group's relationships in detail, and her companion paper in American Museum Novitates examined Tylochromis anatomy as a window onto the phylogenetic position of the African Cichlidae as a whole. Within the genus, robertsi belongs to a cluster of relatively shallow-bodied, elongate forms; Stiassny diagnosed it in part by an unusual lower-jaw skeleton, with the inferior vertebral apophysis short and directed backward rather than following the standard Tylochromis pattern.
Morphology
Tylochromis robertsi reaches about 8.5 in in standard length, placing it among the medium-sized members of a genus that includes both smaller and considerably larger species. The body is comparatively shallow and elongate for a Tylochromis. The predorsal profile rises steeply over the snout — often lending a blunt-nosed look — then is interrupted by a fleshy thickening of the interorbital region before climbing more gently to the dorsal-fin origin, where the back is deepest. The lips are thick and fleshy, the lower jaw frequently inclined slightly from horizontal when the mouth is shut, and the lower pharyngeal jaw is robust, as in all members of this sediment-processing genus. Fin counts run to 14–16 dorsal spines and 12–15 soft rays, three anal spines and 7–8 anal soft rays, over 28–29 vertebrae (usually 29); the lateral-line scale count is 36–40, and the gill rakers are short, broad and widely spaced along the lower limb of the first arch — 14 or 15 of them. The first branched pelvic ray is often drawn out into a filament that can reach past the front of the anal fin, the caudal fin is emarginate and finely scaled to its edge, and the pectorals are rather short. In life the body is a green-grey above and silvery below, washed with bronze; scales on the back and upper flanks are ringed with dark brown to produce a lattice-like pattern, while restricted ventral pigment leaves two or three rows of pale spots along the lower flank. There is a dark brown band over the upper lip and ethmoid region, a short black nape bar, faint traces of about five short bluish vertical stripes that do not cross the midline, a streak of red at the corner of the mouth, and dark brownish-red fins with rows of light spots on the dorsal. Juveniles wear a stronger, zigzagging pattern of broad bars; mature males show characteristic caudal-fin striping that may break into a series of spots.
Habitat
Tylochromis robertsi is a freshwater, benthopelagic fish endemic to the central Congo River basin. Stiassny's material and subsequent records place it along the mainstream middle Congo and through a fan of its right-bank and northern tributaries — the Ubangi and its Uele headwaters (including the Dungu, the type locality), the Kotto, the Mongala, the Itimbiri and the Aruwimi — as well as at Wagenia (Boyoma) Falls near Kisangani, with a single outlying record from the Kama-Elila, a Lualaba tributary. Politically this spans the Democratic Republic of the Congo and the Central African Republic. In terms of freshwater ecoregions the range straddles the Uele, the Cuvette Centrale of the central Congo lowlands, and the Sudanic Congo–Oubangi. These are warm equatorial rivers; FishBase lists a preferred range of roughly 72–77 °F for the species. As a bottom-oriented sediment feeder it is associated with the channels and margins of large rivers rather than with any single specialised microhabitat, and no detailed in-situ chemistry has been published for it specifically. A precise depth band has not been recorded; like other riverine Tylochromis it works the shallow, soft-bottomed margins and shoals of the main channel, so a near-surface to shallow benthic envelope on the order of 0–33 ft is the reasonable working figure pending field measurement.
Feeding
FishBase characterises Tylochromis robertsi as an opportunistic benthic macrophage that feeds mainly on plant material and on insects and their larvae, and it sits low on the food web, with an estimated trophic level near 2.4. This makes it something of a generalist within its genus. The Tylochromini are best known as sand-sifters with heavy, molariform lower pharyngeal jaws adapted to crushing snails and other hard-shelled invertebrates, and the genus as a whole is described as insectivorous and molluscivorous. Tylochromis robertsi keeps the robust pharyngeal apparatus and the broad, well-spaced gill rakers of a sediment processor, but its diet leans toward softer fare — vegetation and aquatic insect larvae winnowed from the bottom — rather than committing to a hard-shelled-prey specialism. Functionally it forages the soft sediments and channel margins of the middle Congo, taking organic material and small invertebrates as opportunity allows.
Mating
Reproductive behaviour in Tylochromis robertsi has not been documented in detail in the wild, but its mating system is reported clearly: it is a maternal (female) mouthbrooder that does not form a pair bond. This places it with the many polygamous African cichlids in which the sexes associate only briefly to spawn and the male contributes nothing to care of the brood. In such a system a ripe female spawns with one or more courting males, takes up the eggs, and thereafter raises the clutch alone, while males invest their effort in display and competition rather than in defending a shared territory. The species shows modest sexual differences consistent with this arrangement — mature males develop the characteristic caudal-fin striping (sometimes resolving into spots) noted in Stiassny's description — but no elaborate nuptial coloration or sustained territoriality has been reported for it. The detailed courtship, spawning site and lek or roving structure remain undescribed.
Breeding
Tylochromis robertsi is a female mouthbrooder: after spawning, the female carries the fertilised eggs and then the developing larvae in her mouth, a strategy that shelters the brood through its most vulnerable stages and frees the parent from defending a fixed nest. Because no pair bond forms, there is no biparental care — the male takes no further part once spawning is over. Specific reproductive figures for this species, such as clutch size, egg dimensions and the duration of brooding, have not been published; what is on record is the mode itself, reported consistently by Stiassny (1989) and in the FishBase compilation. As a guide, mouthbrooding Tylochromis are not especially fecund by cichlid standards, and congeners typically carry modest clutches on the order of a few dozen to perhaps a hundred or so relatively large eggs — the trade-off inherent in oral incubation, where brood size is limited by the volume of the buccal cavity. No spawning of Tylochromis robertsi appears to have been documented in aquaria, so the wild cues that trigger reproduction and the pace of fry development are not known for this species in particular.
In the aquarium
Tylochromis robertsi is essentially an aquarium unknown: it is a Congo-basin riverine cichlid that is not part of the ornamental trade, has no established hobby presence, and does not appear to have been kept or bred in captivity in any documented way. Tylochromis as a genus is regarded as a difficult subject for the home aquarist — these are large, restless, sediment-grubbing fish that want space, current and a deep sand bed to work, and the genus is rarely offered. Anything written here about keeping robertsi specifically would be invention, so the honest position is that no husbandry record exists. If a fish of this type were ever maintained, the sensible starting point would extrapolate from its biology rather than from experience: a long tank with a substantial footprint and a deep bed of fine sand for natural sifting, brisk filtration and gentle to moderate flow to echo the moving river water it inhabits, warm temperatures in the low-to-mid 20s °C consistent with the equatorial Congo, and a varied bottom-oriented diet built around insect larvae and other invertebrate foods with some plant matter, reflecting its role as an opportunistic benthic feeder. Given an adult length around 8.5 in and the genus's general boisterousness, it would be a fish for a large, robust community of similarly sized riverine species rather than a peaceful display tank. None of this is tested, and the species should be regarded as one for the public-aquarium or research setting, not the hobby.
Conservation
The IUCN Red List assesses Tylochromis robertsi as Least Concern (assessed 16 February 2009 by T. Moelants, published 2010), with the population trend listed as unknown. The species is widely distributed through the central Congo River basin and faces no documented species-specific threats, which underpins the Least Concern listing; it carries no CITES listing and is considered harmless to humans. As with most Congo-basin fishes, the relevant pressures are basin-wide and diffuse rather than targeted — deforestation and land-use change in the catchment, expanding artisanal and commercial fisheries, and the sediment, pollution and flow disruption that accompany mining and infrastructure across this vast and still incompletely surveyed drainage. None of these is identified as a present danger to this particular cichlid, and a wide-ranging riverine generalist is far less exposed than the basin's many narrow-range endemics, but the broad data gaps for central Congo fishes mean its status is best read as 'no evidence of decline' rather than as a guarantee of security.