Taxonomy & naming
Cyathopharynx sp. 'green flush' is an undescribed form complex — a recognizable geographic colour morph (or cluster of morphs) documented in the hobby and biotope literature (notably Konings' Cichlid Press titles and the photographic survey at tanganyika.si) but not yet given a formal scientific description. Cyathopharynx belongs to the "featherfin" cichlids — lek-spawning sand-and-rock dwellers whose males build crater bowers and trail greatly elongated, egg-dummy-tipped pelvic fins. Forms in this complex are tracked by trade name pending a formal revision. The Catalog of Fishes is the authority for the valid names.
Morphology
A streamlined cichlid of the intermediate (rock-meets-sand) zone. The sexes differ sharply: nuptial males switch on intense metallic blue-green and gold and grow long pelvic streamers tipped with swollen yellow lappets, while females and non-displaying males stay plain silvery and short-finned. Geographic populations differ mainly in the colour the male turns when displaying; the complex is identified by that local nuptial colour, documented best in photographs rather than prose.
Habitat
Featherfins live where rock gives way to open sand in the well-lit upper zone of the lake. Populations are recorded around Lake Tanganyika part of Lake Tanganyika, where males clear and defend display craters on the sand near rock. The water is hard and strongly alkaline, as everywhere in Tanganyika.
Feeding
A micro-feeder: it grazes fine algal biocover and the micro-invertebrates within it from rock and sand, and picks plankton from the water column when it is available. The long, coiled gut is that of a low-protein grazer — "a lot of food but only a little meat," as Konings put it of the genus — and captive fish do best on a vegetable-based diet.
Mating
Spawning is at a lek: males gather and each builds and defends a sand-crater bower, displaying in full nuptial colour to passing females. There is no pair bond — the male contributes only genes and a crater, and females visit, spawn, and leave to brood alone.
Breeding
A maternal (ovophilous) mouthbrooder. The female lays a small clutch — genus-typically a few dozen large eggs, often fewer — into the male's crater, picks them up, and is fertilized at the male's anal-fin egg-dummies; she then incubates the eggs and larvae in her mouth for several weeks with no male care thereafter.
In the aquarium
Kept for the male's spectacular display, the featherfin needs space, open sand for craters, and hard alkaline water. Single males colour up best; the long pelvic filaments are easily nipped, so tankmates are chosen with care. As with all Tanganyikan locality forms, these populations are kept as single-provenance groups so the local nuptial colour is not lost to cross-breeding.
Conservation
Undescribed forms are not individually assessed by the IUCN. The featherfins are widespread, but individual locality populations are small and easily over-collected; captive-bred, provenance-labelled stock is the responsible choice.