Taxonomy & naming
Peter Humphry Greenwood, the British Museum (Natural History) ichthyologist who spent decades untangling the Lake Victoria cichlid flock, described this fish in 1966 as Allochromis welcommei, in a paper presenting two new Haplochromis species from the lake (Annals and Magazine of Natural History, ser. 13, vol. 8, pp. 303–318). The type series was collected near Damba Island in the northern, Ugandan part of Lake Victoria; the holotype (BMNH 1965.8.6.1) and a substantial series of paratypes and study material are held at the Natural History Museum, London. In his 1980 monograph on the genus, Greenwood judged the species distinctive enough — chiefly for its unusual teeth and its scale-eating habit — to erect a new monotypic genus for it, Allochromis, of which welcommei remains the sole member. Eschmeyer's Catalog of Fishes now treats the valid name as Allochromis welcommei (Greenwood, 1966). This atlas keeps the familiar Haplochromis heading, following the conservative convention (van Oijen et al., 1991) of retaining the lacustrine and riverine Lake Victoria haplochromines in Haplochromis pending a complete revision of the flock — but readers should be aware that the modern, more narrowly drawn genus is Allochromis. The fish belongs to the Pseudocrenilabrinae, the great African cichlid subfamily, and to the Lake Victoria 'superflock' of haplochromines.
Morphology
Allochromis welcommei is a small haplochromine, reaching about 4 in in standard length (FishBase, from the CLOFFA checklist) — a few inches of fish. Like most members of the flock it has the generalised deep-bodied haplochromine shape, but its specialisations are in the mouth: Greenwood diagnosed Allochromis on its unusual dentition and dental pattern, the hardware of a scale-eater. As is typical of Lake Victoria haplochromines, the species is sexually dimorphic in colour, with breeding males developing the bright nuptial coloration the flock is famous for while females remain a more cryptic silvery or brownish — the precise male pattern of welcommei is poorly documented in life, since the species was rare and was largely lost from the lake before modern aquarium photography. Because identification of Lake Victoria haplochromines is notoriously difficult and many species differ only subtly, the dentition and the scale-eating ecology are the most reliable field characters.
Habitat
The species is endemic to the Lake Victoria basin, recorded from the Ugandan and Tanzanian waters of the lake; the IUCN assessment lists Uganda and Tanzania as range states. Within the lake it occupied a range of bottom types, and FishBase notes an ontogenetic habitat shift: smaller specimens were found in sheltered, shallow water over mud, while larger fish moved onto rocky bottoms. The recorded depth range extends to about 46 ft. Lake Victoria itself is a large, shallow, warm equatorial lake straddling the equator; its surface waters are warm year-round (roughly 73–81 °F) and the water is alkaline, with pH generally in the range of about 7.2 to 9.0 — the chemical envelope shared by the whole haplochromine flock. The lake's defining ecological change over the period of this fish's history was a dramatic loss of water clarity through eutrophication, which matters for a flock whose species recognition depends heavily on visual cues.
Feeding
This is the species' claim to fame: it is a lepidophage, a scale-eater, and is generally regarded as the only specialised scale-eating cichlid in the Lake Victoria system. The evidence comes straight from gut contents — examined material held fragments of fin rays and cycloid scales matching those covering the caudal region of other cichlids, while the intestine contained numerous small scales and the empty silica frustules of diatoms ingested incidentally. The picture is of a fish that approaches other cichlids and rasps or plucks scales and fin tissue from their flanks and tails, a feeding mode that requires both specialised teeth (the basis of the genus Allochromis) and behavioural stealth. In trophic classifications of the flock, welcommei is grouped with the scale- and parasite-eating haplochromines (Witte & van Oijen, 1990), guilds that sit apart from the conventional piscivores. FishBase places it at a trophic level around 3.3. Scale-eating is a rare and demanding specialisation worldwide, and welcommei is one of the small number of African cichlids to have evolved it.
Mating
No detailed account of courtship or pair formation in Allochromis welcommei has been published — the species was scarce and disappeared from the open lake before its behaviour could be studied closely. Its reproductive biology is therefore inferred from the broader Lake Victoria haplochromine flock, which is remarkably uniform in this respect. These are polygynous, sexually dichromatic mouthbrooders: males develop bright nuptial colours and display to females, and mate choice in the flock is strongly visual, mediated by male colour against the lake's light environment. There is no lasting pair bond. One consequence specific to this lake's decline bears directly on welcommei: as eutrophication clouded the water, the visual cues underpinning mate recognition broke down, and the IUCN explicitly flags hybridisation under reduced transparency as a potential threat to this species — a reminder that for these fish, courtship and conservation are the same problem seen from two angles.
Breeding
Like essentially all Lake Victoria haplochromines, Allochromis welcommei is a maternal mouthbrooder: after spawning, the female takes the fertilised eggs into her mouth and broods them there through hatching and the early free-swimming stage, releasing fry that can retreat back into her mouth when threatened. The male provides no parental care. Specific figures for this species — clutch size, brooding duration, fry size at release — were never published; the species was lost before such data were gathered. As a genus-typical reference, Lake Victoria haplochromines of this body size are small-clutch brooders, typically carrying on the order of a few dozen eggs (commonly cited at roughly 20–60 for fish of this size), a trade-off of fecundity for the protection mouthbrooding affords. The combination of low fecundity and prolonged maternal care is normal for the flock and helps explain both its explosive speciation and its vulnerability to a novel predator.
In the aquarium
Allochromis welcommei is essentially not an aquarium fish. It is a rare, threatened, scale-eating specialist that vanished from the open waters of Lake Victoria around the mid-1980s and has no established presence in the hobby; there is no body of captive-keeping experience to report, and it should not be confused with the various colourful 'Victorian haplochromines' that are traded (many of those are other species or undescribed forms). For the sake of honesty rather than encouragement: were such a fish ever to be maintained, its scale-eating diet would make it a poor and antisocial tankmate — a dedicated lepidophage harasses and damages other fish by design — and it would need the hard, alkaline, warm water (pH well above 7, temperatures in the mid-20s °C) typical of Lake Victoria. The realistic role for this species in aquarium culture would be a conservation-breeding context, not the general hobby. Anyone wanting to keep Lake Victoria cichlids responsibly is far better served by the robust, well-established haplochromines already in the trade.
Conservation
The IUCN Red List assesses Allochromis welcommei as Vulnerable under criterion D2 (assessed 1 April 2010 by Witte, de Zeeuw & Brooks; published 2016), a category reflecting a very restricted, plausibly precarious situation rather than documented abundance — the population trend is listed as unknown. The principal threat named is predation by the introduced Nile perch (Lates niloticus), whose explosive increase from the 1980s is implicated in the collapse of much of the Lake Victoria haplochromine flock; this is regarded as a potentially reversible pressure. A second, more insidious threat is hybridisation driven by reduced water transparency: eutrophication, erosion and sedimentation have clouded the lake and degraded the visual mate-recognition that keeps these species distinct. The species is also taken incidentally in fisheries, though not specifically targeted. Eschmeyer's Catalog of Fishes flags it as 'probably extinct,' and it was not recorded in the open lake after the mid-1980s despite survey effort (Witte et al., 2016); however, museum records indicate it persisted in at least one Kyoga-system satellite water (Lake Nawampasa), so a categorical extinction is not warranted. Its status should be read against the wider tragedy of the Lake Victoria cichlid flock, one of the largest documented vertebrate extinction events of the twentieth century.