Taxonomy & naming
The species was described by the Belgian ichthyologist Max Poll in 1948, in a paper devoted to the new cichlids that Dr. Jacques Schwetz had collected in the Fwa River of the then Belgian Congo ('Descriptions de Cichlidae nouveaux recueillis par le Dr. J. Schwetz dans la rivière Fwa'). Poll did not place the fish in Cyclopharynx at first. He erected the genus Cyclopharynx for a second, deeper-bodied Fwa snail-crusher, Cyclopharynx fwae, and put the present species in a separate monotypic genus, Neopharynx, as Neopharynx schwetzi. The holotype (MRAC 71290) and nine paratypes are held in the Royal Museum for Central Africa at Tervuren. Both names stood side by side for decades — Kullander and Roberts still listed Neopharynx as valid in the 1991 CLOFFA checklist — until Roberts and Kullander (1994) concluded that Neopharynx was not separable from Cyclopharynx and synonymised the two, producing the combination Cyclopharynx schwetzi (Poll, 1948) used today. The genus thus contains exactly two species, Cyclopharynx fwae and Cyclopharynx schwetzi, both confined to the same water. They sit within the huge African subfamily Pseudocrenilabrinae, among the haplochromine-grade cichlids of the Congo basin, and are most often discussed alongside the other Fwa endemics Poll described in the same era, including Schwetzochromis neodon and the haplochromine now called Thoracochromis callichromus.
Morphology
Cyclopharynx schwetzi is a modest fish, reaching about 4 in total length; aquarium specimens are usually shown at roughly 4–5 in, with males the larger and more colourful sex. The body is slender to moderately deep and laterally compressed, with a fairly pointed snout — noticeably more pointed than that of its congener Cyclopharynx fwae — and a straight or only faintly concave forehead profile. The caudal fin is truncate to subtruncate, slightly more rounded in males than in Cyclopharynx fwae. In good condition the fish is hard to overlook: settled, dominant males glow a bright golden-yellow to almost light-orange over the body, and like many haplochromine-grade cichlids the males carry ocelli (egg-spots) on the anal fin. Females and subdominant fish are plainer, a silvery to greyish brassy tone. The genus's defining structure is internal and not visible in a swimming fish: a massively built, almost spherical lower pharyngeal jaw bone bearing rounded, molariform teeth — the rounded throat-mill that gives Cyclopharynx its name and lets it crack the shells of aquatic snails. Sexual dimorphism is therefore expressed mainly in size and colour: bright golden, egg-spotted, larger males versus duller, smaller females.
Habitat
The entire known range of the species is the Fwa, an isolated, exceptionally clear body of water in the Kasai drainage of the middle Congo basin, in the central Democratic Republic of the Congo (the Fwa drains via the Lubu River into the Kasai). The literature consistently records it from the 'rivière Fwa', and FishBase maps it strictly to the Fwa River; in the aquarium hobby the same water is almost always called 'Lake Fwa' or 'Lac Fwa', reflecting its still, lake-like, spring-fed clarity. Either way it is a single, small, hydrologically isolated system, and that isolation is the whole story of the genus — Cyclopharynx evolved in place and never spread. The water is warm, clear and well-oxygenated tropical freshwater; the basin sits squarely in the lowland equatorial tropics (FishBase brackets the range at roughly 5°N–10°S). No detailed in-situ chemistry has been published in the readily available literature, so aquarists work from the general profile of clear central-Congo waters: warm (about 75–82 °F) and circumneutral to mildly alkaline rather than the soft blackwater of the Congo mainstem, with reported keeping pH spanning roughly 7.0–8.5. As a benthic snail-crusher it lives over and among hard substrates where its molluscan prey occurs; published depth figures for this specific water are not available, so the depth band here is given as the shallow, sunlit zone typical of such clear standing waters rather than a measured range.
Feeding
Cyclopharynx is the snail-crusher of the Fwa. The genus is built around a hypertrophied, rounded lower pharyngeal jaw set with blunt molar-like teeth — a crushing mill that processes hard-shelled prey, the classic durophagous (mollusc-crushing) adaptation seen convergently in several lake cichlid lineages. In life the fish forages over the bottom, taking snails and other shelled invertebrates and grinding them in the throat. FishBase additionally reports the species as 'mainly feeds on algae and diatoms', so the working picture is a benthic generalist that grazes aufwuchs and biofilm from hard surfaces while also crushing molluscs when it finds them, rather than a strict, exclusive snail specialist. Hobbyist observation echoes this flexibility: kept fish graze algae from rocks and will also opportunistically take small fry. In the wild community its durophagous niche is what separates it from the Fwa's other endemic cichlids, which partition the same small water by diet and microhabitat.
Mating
As a maternal mouthbrooder, the species follows the haplochromine-grade reproductive script rather than forming the lasting pair bonds of substrate-spawning cichlids. There is no published field study of courtship in the wild Fwa, so the account here is built from its FishBase-confirmed mode (ovophilic, maternal mouthbrooder) and from how the fish behaves in aquaria. Males are the showy, territorial sex: a dominant male intensifies to bright gold, takes up and defends a small territory or display site, and courts ripe females with the lateral displays and quivering typical of the group. Egg-spots on the male's anal fin play their usual role in spawning. Outside of active breeding the species is comparatively peaceful for an African cichlid — keepers describe it as relatively mild-mannered next to the notoriously combative Fwa haplochromine Thoracochromis callichromus — but a spawning male will still hold and defend his patch. Females are not territorial in the same way and do the parental work.
Breeding
Cyclopharynx schwetzi is an ovophilic maternal mouthbrooder: the female takes the fertilised eggs into her mouth and broods them there, the eggs being fertilised inside or at the mouth with the assistance of the male's anal-fin egg-spots, exactly as in the Congo and rift-lake haplochromines it resembles. The female alone incubates the clutch, holding the developing eggs and then the larvae in her buccal cavity for the standard several weeks until the fry are released as free-swimming, fully formed young; she may continue to shelter them in her mouth at the first sign of danger for a short while afterward. No clutch count specific to this species appears in the accessible literature; for a 4 in mouthbrooder of this type a genus-typical brood is small, on the order of a few dozen eggs rather than the hundreds a large substrate-spawner produces. Aquarists have spawned the species — it is in private collections precisely because it can be bred — and report the broods of small, well-developed fry expected of a maternal mouthbrooder, with males emerging gold and egg-spotted as they mature. Because the female carries everything internally, no nest, cave or spawning substrate is required beyond a settled, low-stress environment.
In the aquarium
This is a rare, specialist fish, not a beginner's African cichlid, and for most of its history it was a genuine 'holy grail' species — known from museum specimens and a handful of importers long before live fish reached hobbyists in any number. When it does appear it is expensive and trades on its Fwa-endemic provenance. Anyone keeping it is effectively running a small ark population for a fish that barely exists in captivity, which is why all four of the Fwa endemics, this one included, are carried on the CARES Conservation Priority list.
Kept fish are, by African-cichlid standards, relatively peaceful. The most reliable hobby accounts describe Cyclopharynx schwetzi as the mild member of a Fwa community and pair it with its tougher endemic neighbour Thoracochromis callichromus, which is more aggressive and tends to throw male-heavy spawns. A group in a tank of roughly 55 US gal or larger is sensible, with the footprint mattering more than the height; keeping several fish lets a male colour up and display while spreading any aggression. Provide a rocky, hard-surfaced layout with open foraging room — the fish grazes algae from rock and works the bottom for snails — and clean, well-filtered, well-oxygenated water.
Water should be warm and clear: about 75–82 °F, with pH in the neutral-to-mildly-alkaline band (roughly 7.0–8.5) that suits a clear central-Congo water rather than the soft, acidic blackwater regime used for Congo-mainstem fishes. It is not a hard-rift-lake fish and does not need the very high pH and carbonate hardness of a Tanganyika or Malawi tank. Feeding is straightforward for a willing grazer and crusher: it accepts prepared foods, takes algae and biofilm, and will use its pharyngeal mill on small snails offered as enrichment; a varied diet keeps the gold colour bright. The main husbandry cautions are its rarity (a loss is hard to replace), its appetite for small fry that rules out mixing it with tiny tankmates, and the simple fact that almost everything written about its captive needs is inferred from a small circle of keepers rather than from a deep published literature — so a careful, conservative approach is warranted.
Conservation
The IUCN Red List assesses Cyclopharynx schwetzi as Least Concern (assessed 16 February 2009 by T. Moelants; published 2010). That category reflects the absence of a documented decline at the time of assessment rather than any wide safety margin — this is a single-water endemic, and a Least Concern rating for a fish restricted to one small, isolated system should be read cautiously. The aquarium-conservation community treats it as genuinely at risk: it is listed by CARES, the hobbyist program that maintains captive populations of cichlids threatened in the wild, alongside the three other Fwa endemics. The Fwa's whole biological interest comes from its isolation, and that same isolation is its vulnerability — a fish found in exactly one water has no refuge if that water is degraded by siltation, deforestation in its catchment, pollution, or the introduction of competitors or predators, pressures that bear on small Congo-basin systems generally. There is no CITES listing. The conservative course is to treat Cyclopharynx schwetzi as a narrow-range endemic whose long-term security depends both on the integrity of the Fwa and on the maintenance of healthy captive lineages.