Taxonomy & naming
Haplochromis relictidens was described in 2019 by Nathan Vranken, Maarten Van Steenberge and Jos Snoeks in the journal Hydrobiologia, as part of a revision titled 'Grasping ecological opportunities: not one but five paedophagous species of Haplochromis (Teleostei: Cichlidae) in the Lake Edward system.' The holotype, an adult of 4.5 in standard length, is registered as MRAC 2017.006.P.0007 in the collection of the Royal Museum for Central Africa at Tervuren, Belgium, with paratypes split between that museum and the Royal Belgian Institute of Natural Sciences. The type locality is the mouth of the Kazinga Channel over hard substrate, in Lake Edward (roughly 0°12′S, 29°53′E). The revision examined sixty-eight specimens of long-jawed, small-toothed haplochromines and concluded that what had been treated as one or two paedophagous species in the lake was in fact five: the previously known Haplochromis taurinus, a reassessed Haplochromis paradoxus shown also to be paedophagous, and three species new to science — Haplochromis gracilifur, Haplochromis molossus and Haplochromis relictidens. The genus name Haplochromis is retained here, though it functions as a holding name: the East African haplochromine flocks are a vast, recently radiated assemblage whose generic boundaries remain unsettled, and many authors place these species in or near Haplochromis pending a comprehensive revision. No synonyms have been proposed for so recently described a species.
Morphology
This is a modestly sized cichlid: the type series reached a maximum of about 4.5 in standard length. The body is the laterally compressed, deep-headed form typical of haplochromines, with a dorsal fin of 15–16 spines and 7–10 soft rays, an anal fin of 3 spines and 8–9 soft rays, and 29 vertebrae. The diagnostic features lie in the jaws and teeth, and they are the source of the name. In large specimens (over about 3.5 in SL) the lower jaw is slender and acutely pointed while the upper jaw is rounded, so that the anterolateral parts of the upper jaw remain visible from below — an unusual configuration among the lake's cichlids. The outer teeth are very small, blunt to rounded, widely and irregularly spaced, and notably few: only 16–26 in the outer row, against 22–65 in related species. Most strikingly, the number of outer teeth decreases as the fish grows, a reduction the describers built into the epithet. These features separate it from the other Lake Edward paedophages: Haplochromis taurinus, Haplochromis molossus and Haplochromis gracilifur all have stouter lower jaws, and Haplochromis paradoxus a narrower head. Live coloration is known chiefly from mature males, which are green-gold with bright red flanks crossed by very faint vertical bars — a pattern distinct from that of the other paedophagous species in the system, and one of the live-colour cues the authors used to tell the radiation apart.
Habitat
Haplochromis relictidens is endemic to the Lake Edward system, the cluster of waters straddling the border between the Democratic Republic of the Congo and Uganda that comprises Lake Edward, the smaller and shallower Lake George, and the Kazinga Channel that links them. Lake Edward sits at about 2992 ft elevation in the western branch of the East African Rift, with a surface area near 2,186 mi², a maximum depth of roughly 384 ft and a mean depth of about 121 ft. Like other rift lakes its waters are mineral-rich and alkaline, typically running warm and well-buffered at the surface with pH in the upper-neutral to alkaline range and high conductivity; published basin surveys report wide swings once tributaries and inflows are included, but the open lake itself is a hard, alkaline water body. The known records of Haplochromis relictidens come from hard substrate at the mouth of the Kazinga Channel, a shallow, current-swept zone where the channel meets the lake. The species is benthopelagic — it works near the bottom but ranges up into the water column. Because the fish is documented from so few collections, its full distribution and depth range within the system are not yet well mapped.
Feeding
Haplochromis relictidens is a paedophage — a predator on the eggs and larvae of other cichlids. In the haplochromine flocks of the East African lakes, paedophagy most often takes the form of robbing brooding females: a paedophage harasses a mouthbrooding female and induces her to spill or release her clutch, then snatches the eggs and fry. The long, slender oral jaws set with small, sparse teeth that define this species are the morphological signature of that guild — adaptations for engulfing soft, slippery young rather than for crushing snails, scraping algae or seizing adult fish. Stomach-content observations made during the 2019 revision confirmed the paedophagous diet for the species. Its trophic position is therefore high among the lake's cichlids despite its small size, since it consumes the most vulnerable life stage of its relatives. Paedophagy has evolved repeatedly and independently within these flocks; the discovery that the Lake Edward system supports five distinct paedophagous species, rather than the one or two long assumed, was the central finding of the study that named this fish, and a vivid example of how finely the haplochromine radiation has partitioned a single feeding strategy.
Mating
No courtship or pair-formation behaviour has been described specifically for Haplochromis relictidens, which is known only from preserved and freshly collected specimens rather than from sustained field or aquarium observation. Its reproductive biology can only be inferred from the well-studied pattern shared across the haplochromine cichlids of the East African lakes. In that pattern, mating is polygynous and promiscuous: there is no lasting pair bond. Males develop their brightest nuptial colours when ready to breed — in this species the green-gold body and red flanks of mature males — and display to passing females, often over a small temporary territory or display site, to solicit spawning. The conspicuous, species-specific male colour pattern is itself the key reproductive signal that keeps these closely related, recently diverged species from interbreeding, which is precisely why the describers relied on live male colours to separate the five paedophages of the system. Beyond this general framework, the species-level details of its mating remain undocumented.
Breeding
Breeding has not been directly documented for Haplochromis relictidens, but its mode can be stated with confidence from the biology of the group: like essentially all haplochromine cichlids of the East African lakes, it 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 the fry once they can fend for themselves and, in many species, briefly taking them back in when threatened. Clutch sizes in small haplochromines of this size class are modest — typically a few tens of eggs, on the order of 10–40, the exact figure unrecorded for this species. There is a pointed irony in a maternal mouthbrooder that makes its living as a paedophage: the very brooding behaviour that protects this species' own young is the behaviour it exploits in others, raiding the mouths of brooding females of neighbouring cichlids for their eggs and larvae. No data exist on fry development, breeding season or spawning triggers for Haplochromis relictidens specifically.
In the aquarium
Haplochromis relictidens is not an aquarium fish. It was described in 2019 from museum and field collections, is known only from the Lake Edward system, and does not appear in the ornamental trade; there are no established husbandry accounts for it, and it is most unlikely to be encountered by hobbyists. Anything written about keeping it would be extrapolation from its better-known relatives rather than experience with the species itself. If it were ever maintained, the reasonable expectations would follow from its origins and habits: hard, alkaline, well-filtered water in the broad range that suits East African rift cichlids (roughly pH 7.5–9 and warm temperatures around 73–81 °F), a tank with open hard-bottom areas reflecting the channel-mouth habitat, and the understanding that a dedicated paedophage is a difficult and unrewarding subject — it is adapted to rob the broods of other mouthbrooders, so it would be actively destructive to any cichlid breeding in the same tank. For now the honest statement is simply that this is a wild, very recently described species with no aquarium history.
Conservation
Haplochromis relictidens has not been evaluated by the IUCN Red List; its conservation status is formally Not Evaluated, as is typical for a cichlid described only in 2019. That absence of a rating should not be read as reassurance. The species is a narrow-range endemic known from very few specimens at a single area of one rift lake, and the Lake Edward system as a whole faces mounting pressure: a growing lakeside human population, intensifying and partly unregulated fishing, catchment deforestation and erosion, pollution, and the looming prospect of oil exploration in and around the Virunga–Queen Elizabeth protected-area complex that frames the lake. The wider region's cichlid history is also a cautionary one — the catastrophic collapse of the Lake Victoria haplochromine flock after the introduction of Nile perch shows how quickly these endemic radiations can unravel. Lake Edward has so far escaped that particular fate, lacking an established Nile perch population, but its haplochromines remain poorly surveyed and undefended. For Haplochromis relictidens specifically there are no population data at all, and a baseline assessment would be the necessary first step toward judging its status.