Taxonomy & naming
Teleogramma gracile was described by the Belgian-British ichthyologist George Albert Boulenger in 1899, in his account of new Congo fishes published in the Annals of the Congo Museum, and it is the type species of the genus Teleogramma Boulenger, 1899. The holotype (a single specimen, MRAC 73) was registered from "Matadi" in the present-day Democratic Republic of the Congo, though the Catalog of Fishes and later workers regard that type locality as probably erroneous — the species is reliably known from rapids upstream of Matadi rather than the town itself. So strange was the fish's elongate, flattened body that Boulenger originally placed the genus not in the Cichlidae but in the wrasse family Labridae; George S. Myers (1939) recognised it as a cichlid, and Takahashi & Nakaya (2001) provided a detailed osteological and myological description that formally allocated the genus to the Cichlidae and listed a suite of synapomorphies uniting its species. Within the family, Teleogramma belongs to the subfamily Pseudocrenilabrinae; a multilocus phylogeny by Schwarzer and colleagues (2014) nested it firmly within the chromidotilapiine lineage, an early, primarily riverine West- and Central-African radiation whose origins predate the great lacustrine flocks of East Africa. The genus was long held to contain four species — Teleogramma gracile, Teleogramma brichardi, Teleogramma depressa and the upstream Teleogramma monogramma — until Stiassny & Alter (2015) added the deepwater snail-eater Teleogramma obamaorum, bringing the total to five. In their molecular tree, Teleogramma gracile falls within a closely knit "clade B" of lower-Congo populations whose extremely short branch lengths and conflict between morphology and DNA hint at rapid, recent divergence and possible ongoing gene flow among incipient species.
Morphology
Teleogramma gracile is a small cichlid: FishBase records a maximum of about 3 in standard length, and members of the genus as a whole barely reach 4 in. The body is the hallmark of the genus — elongate, laterally compressed toward the rear, with a markedly dorsoventrally flattened head that lets the fish press itself low against rock in fast current. A pair of prominent tubular nostrils projects from the snout, and the lateral line runs as a single continuous canal rather than splitting into the separate upper and lower branches seen in most cichlids; these features, together with details of the jaws and gut, are diagnostic for Teleogramma. Teleogramma gracile is separated from its congeners chiefly by its lower lateral-line scale count (about 33–35 pored scales, versus the much higher counts of Teleogramma brichardi), a slightly more pointed snout, somewhat more elevated eyes, and, in some males, several vertical rows of dark maculae (spots) in the caudal fin. Base coloration is a sombre grey-brown, fitting for a fish that lives among dark, current-scoured rock. The species is strongly sexually dimorphic in a way typical of the genus: ripe females develop a distinctively marked, contrastingly coloured dorsal "blaze" on the caudal fin and a pronounced red flush across the belly — a breeding-condition signal that males lack — a dichromatism Roberts & Stewart documented across the lower-Congo Teleogramma in their 1976 survey.
Habitat
The species is a lower-Congo endemic, restricted to the rapids of the lower Congo (Zaire) River in the Democratic Republic of the Congo, with FishBase also citing records from the Republic of the Congo on the opposite bank. Verified collection localities lie in the rapids country between Pool Malebo and Matadi — among them Lenga Lenga near the first chutes beyond Pioka, Bulu and Tadi west of Luozi near Kibunzi, and the Luozi region itself, where specimens come from rocky margins of the main channel. This is an extreme rheophilic biotope: the lower Congo carries one of the largest discharges of any river on the planet through a series of cataracts and deep bedrock canyons, generating turbulent, fast, well-oxygenated flow. Teleogramma gracile is a benthic, rock-associated fish of these rapids, sheltering in crevices and interstices among current-swept boulders and outcrops rather than in open water. The river here is warm tropical freshwater — broadly soft and near-neutral, in the range that suits most lower-Congo cichlids — but it carries a heavy sediment load and intense humic staining from the upstream Cuvette Centrale, so the water is turbid and light attenuates rapidly, by Stiassny's field observation within roughly the first half-metre to metre below the surface. FishBase classes the species as demersal; precise in-situ depth, temperature and chemistry for Teleogramma gracile specifically are not well documented in the literature, and the figures used here reflect the genus's shallow rocky-rapids habitat and the general chemistry of the lower Congo.
Feeding
Teleogramma is an insectivorous genus, and Teleogramma gracile feeds as a benthic invertebrate-picker of the rapids. Gut-content work summarised by Stiassny & Alter (2015) found the lower-Congo congeners to be almost exclusively insectivorous, taking aquatic larvae and nymphs — principally mayflies (Ephemeroptera), and to a lesser extent caddisflies (Trichoptera), stoneflies (Plecoptera) and chironomid midges — extracted from rock surfaces and from the interstices between stones. (The one dietary outlier in the genus is the recently described deepwater species Teleogramma obamaorum, which has switched to crushing small gastropods; Teleogramma gracile retains the ancestral insectivorous habit.) FishBase places the species at a trophic level of about 3.3. Functionally, then, Teleogramma gracile works the biofilm-and-invertebrate community of the rock substrate, gleaning the larval insects that cling to current-scoured surfaces in a habitat where the relentless flow continually delivers drifting prey. Its slender, flattened build and crevice-dwelling habits keep it within the boundary layer close to the rock, where it can forage without being swept off by the main current.
Mating
Like its congeners, Teleogramma gracile is a pair-bonding cichlid, and FishBase characterises the species succinctly as rheophilic and pair-bonding. In the rapids, individuals are territorial around the rock crevices that serve both as shelter and as spawning sites. Pair formation is mediated by the genus's striking sexual dichromatism: a female coming into breeding condition advertises her state with the contrastingly marked dorsal blaze on her tail and the red flush spreading across her belly, visual signals directed at a prospective male. This female-driven courtship coloration is a recurring theme among the chromidotilapiine cichlids to which Teleogramma belongs, where females are often the more brightly ornamented sex in breeding dress. The detailed courtship sequence of Teleogramma gracile has not been described in the wild, but in the closely related and aquarium-kept Teleogramma brichardi, courtship involves the pair meeting at the cave entrance with quivering and lateral display before the female leads the male inside — behaviour that is a reasonable model for this slender congener. Pairs defend the immediate vicinity of their chosen crevice through the spawning period.
Breeding
Teleogramma gracile is a cave spawner. FishBase records the genus reproductive mode plainly as pair-bonding and cave-spawning, and the species follows the chromidotilapiine pattern of laying a small clutch of adhesive eggs on the roof or wall of a sheltered cavity — in the wild, a crevice between rapids boulders. Fecundity is low, as befits a small fish that invests in concealment and parental care rather than egg numbers: Stiassny & Alter (2015) counted only 15–19 mature eggs (each about 0.5 in) in ripe females of the deepwater congener Teleogramma obamaorum, and reported that ripe females of the similarly sized Teleogramma brichardi and Teleogramma monogramma carried higher counts averaging roughly 25–35 eggs, which is the best available genus-typical estimate for the clutch of Teleogramma gracile. Care is biparental in the cave-spawning chromidotilapiine manner, with the female tending the eggs and wrigglers inside the cavity while the pair guards the territory; the precise division of labour and the developmental timetable have not been documented for wild Teleogramma gracile. The spawning of this particular species has rarely if ever been reported in detail in captivity, but its better-known relative Teleogramma brichardi has been bred in aquaria, the female laying creamy-white eggs on a cave ceiling and guarding the brood — a reasonable template for what Teleogramma gracile does in the wild.
In the aquarium
Teleogramma gracile is very much a specialist's fish and is rarely seen in the hobby; its rapids-dwelling relative Teleogramma brichardi (Brichard's slender cichlid) is the genus's only at-all-common aquarium representative, and most husbandry guidance for the genus derives from it. Anyone attempting Teleogramma gracile should treat it as a small, current-loving, territorial rheophile. The defining requirement is flow and oxygen: these are fish of cataract water, so a powerhead or strong circulation pump and brisk turnover are essential, along with the high dissolved oxygen that comes with it. The aquascape should be built from stacked rock and stone to create a maze of caves and crevices — both shelter and potential spawning sites — over a substrate of sand or smooth gravel, with the structure giving subordinate or non-receptive fish places to break line of sight. A footprint on the order of a 35.5 in / 30-gallon tank or larger suits a small group of these little cichlids; like other rheophilic Congo dwarves, they hold territories and the aggression is manageable in an over-structured tank but escalates in a bare one. Water should be warm, soft to medium and around neutral, roughly pH 6.5–7.5 and 75–82 °F, mirroring the lower Congo; clean, well-filtered conditions matter, as rapids fish are adapted to highly oxygenated water and tolerate fouling poorly. Diet in captivity should lean on small live and frozen invertebrate foods — bloodworm, daphnia, brine shrimp, and similar — reflecting the insectivorous wild diet, supplemented with quality sinking prepared foods that the fish can take from the bottom. Tankmates, if any, should be other small, current-tolerant Congo rapids species kept with awareness of the strong intraspecific territoriality at spawning time. It should be said plainly that detailed, reliable captive accounts of Teleogramma gracile specifically are scarce; the parameters above are extrapolated from its biotope and from the keeping of its congener Teleogramma brichardi.
Conservation
The IUCN Red List assesses Teleogramma gracile as Vulnerable under criterion D2 (assessed 16 February 2009 by T. Moelants; published 2010), the listing reflecting a very restricted range in the lower Congo rapids in which a localised threat could rapidly affect the whole population. The population trend is recorded as unknown, and the species carries no CITES or CMS listing. The principal flagged threat is potential future mining in the Luozi region, one of the species' core localities; more broadly, the lower Congo rapids — a global hotspot of fish endemism, home to many narrow-range cichlids, mormyrids and catfishes found nowhere else — face pressure from hydroelectric development on the river's enormous hydraulic gradient (the Inga dam complex sits squarely within Teleogramma habitat), from sedimentation, and from the inherent vulnerability of species confined to a single short stretch of an extreme and hard-to-survey environment. As a small, geographically restricted endemic of this remarkable river, Teleogramma gracile is exactly the kind of species whose fate is tied to the conservation of the rapids themselves.