Taxonomy & naming
Teleocichla cinderella was described by the Swedish ichthyologist Sven O. Kullander in 1988, in the landmark Copeia paper 'Teleocichla, a new genus of South American rheophilic cichlid fishes with six new species' (Copeia 1988(1): 196–230). That single work created the genus and named all six of its original members at once: Teleocichla centrarchus (the type species), Teleocichla gephyrogramma and T. monogramma from the Rio Xingu, Teleocichla prionogenys and Teleocichla proselytus from the Rio Tapajós near Itaituba, and Teleocichla cinderella from the Rio Tocantins near Tucuruí. The name has stood unchallenged as the original combination ever since, and the nomenclatural act is registered in ZooBank. Kullander coined the genus name to flag the striking parallel between these fishes and the African rheophilic cichlids of the genus Teleogramma from the Congo: both are slender, worm-shaped, reduced-swimbladder rock-dwellers, though the resemblance is convergence rather than kinship. Within the New-World cichlid subfamily Cichlinae, Teleocichla belongs to the eartheater tribe Geophagini and sits close to the pike cichlids Crenicichla, with which it shares an elongate body and long, narrow head — but it differs critically in the mouth, having a small, downturned, non-predatory gape suited to picking tiny prey rather than the wide ambush jaws of a pike. The type locality, on the Tocantins at Tucuruí, is the source of the species' poignant footnote: it was submerged by the Tucuruí dam reservoir only a few years after the description, and the population's status there has been uncertain ever since.
Morphology
This is a dwarf cichlid. FishBase, following Kullander's 2003 checklist, gives a maximum standard length of about 2 in — roughly 3 in in total length — and the largest specimen in Kullander's original 1988 type series measured 3 in (about 3 in) SL, which the describer pointed to as an emphasis of just how small these fishes are. (A figure of 5.5 in TL circulates in some compilations, but it is far above every measured specimen and is best regarded as an error or a mix-up with one of the larger undescribed congeners.) The body is the elongate, cylindrical, slightly worm-like form typical of the genus, with a long low head, a small terminal-to-subterminal mouth, and a reduced swim bladder that keeps the fish negatively buoyant and pinned to the bottom — an adaptation to life in current rather than open water. Coloration is deliberately understated: shades of grey and black, mottled and barred, that give the fish an 'ashy' appearance against wet rock. It is precisely this drab, sooty livery that Kullander invoked in the species name, a play on the fairy-tale Cinderella by way of the Latin word for ashes. As in the genus generally, the markings are cryptic camouflage rather than display; bright nuptial colour, where it appears at all in Teleocichla, is confined to the fins of territorial males. Sexual dimorphism in this particular species is poorly documented, but in Teleocichla as a whole territorial males develop longer, more colourful unpaired fins than the plainer females and subordinates, and ripe females become noticeably fuller-bodied.
Habitat
Teleocichla cinderella is endemic to Brazil and, as far as is known, to the lower Rio Tocantins basin within the greater Amazon drainage — its type and only confirmed locality being the rapids at Tucuruí, in the state of Pará. Like all members of its genus it is strictly rheophilic, a creature of fast, well-oxygenated clearwater rapids rather than the slow, weedy backwaters favoured by most small Neotropical cichlids. The Tocantins is a clearwater river draining the crystalline Central Brazilian Shield, and its rapids run warm, soft and only mildly acidic. No in-situ chemistry was published for the now-drowned Tucuruí site itself, but field measurements made by Rainer Stawikowski and colleagues in the directly comparable rapids of the Rio Xingu give a reliable picture of the habitat: clear water of about pH 6.5, very soft (around 1 degree of general hardness and less than 1 degree of carbonate hardness), low conductivity near 120 microsiemens, and a water temperature that during the low-water season climbed to roughly 90 °F, with shallow margins reaching the mid-30s. FishBase brackets the genus tolerance even wider, at 75–99 °F. The fish occupy the rocky main-river bottom in shallow water — typically around a metre deep at low water, far deeper and far swifter when the river is in flood — sheltering in pits, crevices and beneath flat stones. There they hold station in the current by turning their pectoral fins out flat like aeroplane wings, so that the rushing water presses them down onto the rock instead of sweeping them away.
Feeding
Where the related pike cichlids are predators that ambush other fish, Teleocichla took a different evolutionary path, and its small downturned mouth is the key. Observers have compared it to the mouth of a marine dragonet (family Callionymidae): a modest gape built not for seizing large prey but for picking small items off the substrate. Teleocichla cinderella is therefore a benthic micro-invertebrate forager, working over and into the rock for tiny crustaceans, insect larvae and other small animals living in the thin film of algae and detritus (the aufwuchs) that coats current-swept stone; some congeners have also been seen snapping at invertebrates drifting past in the current while peering out from a crevice. FishBase places the genus at a trophic level around 3.1, consistent with a small carnivore-leaning omnivore rather than a herbivore or a piscivore. Kullander suggested this 'callionymid mouth' was the decisive innovation that let Teleocichla colonise the rapids niche without competing head-to-head with other cichlids — a small fish exploiting a food supply the larger rheophilic Crenicichla could not efficiently reach.
Mating
The reproductive behaviour of Teleocichla cinderella has not been observed in the wild, and the species has barely, if ever, entered the aquarium trade, so what can be said is drawn from its better-studied congeners and from the genus's general biology. Teleocichla are territorial rock-dwellers: adult males hold and defend small territories centred on a pit, a hole in a stone, or the space beneath a flat rock, advertising ownership with spread, colour-flushed fins, and retreating into cover when threatened. Species differ markedly in temperament — some are relatively social and tolerant, others sharply aggressive — and several Teleocichla species are syntopic, packed so tightly into the same rapids that observers once found at least three different species sheltering under a single rock. With so little spatial separation, reproductive isolation between the species is thought to rest on behavioural barriers — differences in courtship, colour and timing — rather than on the use of separate microhabitats. Pair formation in the genus, where documented, follows the substrate-spawner pattern: a male and a ripe female form a temporary bond on his territory, with the female taking on the bulk of brood care once eggs are laid.
Breeding
No spawning of Teleocichla cinderella has been documented, and its breeding biology must be inferred. Like other members of the genus, and like the closely allied dwarf Crenicichla of the same Tocantins–Xingu rapids, it is a cave or crevice substrate spawner: the eggs are attached to the roof or wall of a sheltered cavity among the rocks rather than scattered or mouthbrooded. German aquarists succeeded in spawning at least one Teleocichla species in the late 1980s, confirming the cave-spawning, biparental-to-female-tended pattern for the genus, but no detailed fecundity figures specific to Teleocichla cinderella exist. By analogy with the dwarf rheophilic cichlids it lives alongside — the small Crenicichla of the Tocantins rapids produce clutches on the order of a few dozen to a few hundred eggs laid on a hidden surface and guarded, typically by the female, with the male patrolling the territory — a modest clutch of perhaps a few dozen to around a hundred eggs guarded in a rock crevice is the most reasonable expectation. The free-swimming fry would be expected to remain close to the parental shelter and bolt back into cover at any disturbance, as is the rule for crevice-spawning rheophilic cichlids. These figures are genus-typical estimates, not measurements of this species.
In the aquarium
Teleocichla cinderella is essentially absent from the aquarium hobby and should be regarded as a fish for advanced specialists at best — and, given its conservation status and the loss of its type locality, one that hobbyists are unlikely to encounter at all. The wider genus has a hard-won reputation for being extraordinarily difficult to obtain and keep: the fish are very hard to catch in their rapids, they ship notoriously badly (exporters have refused to guarantee live arrival), and they do not tolerate being moved into a still, non-rheophilic tank. American aquarists who managed to import congeners such as T. monogramma in the early 1990s described losing nearly the entire shipment within days. Anyone attempting a Teleocichla must recreate the rapids: a long tank with powerful, well-oxygenated flow (multiple powerheads or a river-tank manifold), spotless warm soft water in the range the wild fish experience — roughly 79–90 °F, pH about 6.0–7.0, very low hardness and conductivity — and a floor of smooth water-worn rocks and cobbles providing the crevices and flat-stone shelters these territorial fish require. Pristine water quality and high dissolved oxygen are non-negotiable; these are not fish that forgive a sluggish, organically loaded tank. Feeding would centre on small live and frozen foods — bloodworm, Daphnia, Cyclops, brine shrimp and the like — offered into the current to mimic the substrate-picking the fish does in the wild. Tankmates should be other small rapids specialists or nothing at all; the territoriality typical of the genus makes crowding risky in anything but a large, structurally complex tank. In honest terms, this is a species almost no aquarist will keep, and the genus as a whole remains a connoisseur's challenge rather than a practical pet.
Conservation
The IUCN Red List assesses Teleocichla cinderella as Endangered (EN), under criteria B2ab(iii,v); the assessment was carried out on 7 November 2018 by Brazil's Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio) and published in 2022. The category reflects a very small known range concentrated at a single area in the lower Tocantins together with continuing decline in the extent and quality of its rapids habitat. The proximate cause is starkly concrete: the species' type — and only confirmed — locality, the rapids at Tucuruí, was inundated by the reservoir of the Tucuruí hydroelectric dam within a few years of the fish being described, converting fast, rocky, oxygen-rich rapids into deep, still impoundment water that a reduced-swimbladder, current-dependent specialist cannot inhabit. Damming is the defining threat to the whole Tocantins–Xingu rheophilic cichlid fauna, and Teleocichla cinderella is among its clearest casualties; the Tocantins basin has since been further fragmented by additional hydroelectric projects, and the comparable Xingu rapids — home to several sister species — have been transformed by the Belo Monte complex. Whether Teleocichla cinderella persists in any remaining rapids fragment upstream or downstream of the Tucuruí reservoir is genuinely uncertain. It carries no CITES or CMS listing, and it is of no fishery importance; its fate rests entirely on whether any of its specialised rapids habitat survives the basin's continuing dam development.