Taxonomy & naming
Mazarunia charadrica was described in 2012 by Hernán López-Fernández, Donald C. Taphorn and Elford A. Liverpool, in a paper in Neotropical Ichthyology (volume 10, number 3, pages 465–486) that gave the previously monotypic genus Mazarunia a phylogenetic diagnosis, redescribed the type species Mazarunia mazarunii, and erected two new species — charadrica and pala. The species had been flagged in the literature two years earlier as 'Mazarunia sp. 1' in López-Fernández et al.'s 2010 study of relationships within the eartheater tribe Geophagini, then formally named once the authors had assembled enough material. The holotype, an adult of 2.5 in standard length, is catalogued UG/CSBD 1667 (ex-ROM 83808) in the fish collection of the Center for the Study of Biodiversity at the University of Guyana in Georgetown, and was taken from a shallow pool in Waruma Creek in the upper Mazaruni drainage in April 2008; an extensive paratype series, much of it housed at the Royal Ontario Museum in Toronto, spans the Kukui River and other tributaries. The genus sits in the subfamily Cichlinae, tribe Geophagini — the South American eartheaters — and its closest relative is Guianacara, another Guiana-Shield genus; that sister-group relationship was the central result of the 2012 phylogenetic analysis. Mazarunia is diagnosed by an unusual osteological feature shared with no other cichlid: the complete loss of the sixth infraorbital bone. Among its own three species, Mazarunia charadrica is set apart by the structure of its first epibranchial bone (the uncinate process and anterior arm of roughly equal width, with reduced anteroventral expansion), by cycloid scales on the opercle, postorbital, lateral chest and anal-genital regions where its congeners have ctenoid scales, by the absence of the mid-lateral spot present in both Mazarunia mazarunii and Mazarunia pala, and by the diffuse dark 'cap' over the top of the head. The specific name is feminine and the original combination has stood unchanged.
Morphology
Mazarunia charadrica is a small cichlid; FishBase records a maximum of 3.5 in in standard length, making it modestly larger than the type species Mazarunia mazarunii (about 2 in SL) and comparable to its congener Mazarunia pala, but still firmly in dwarf-cichlid territory. The body is moderately deep and laterally compressed, the head broadens slightly toward the throat, and the mouth is subterminal — set a little below the tip of the snout — in keeping with a fish that picks food from the bottom. The fin counts run to roughly 15–17 dorsal spines and 8 soft rays, three anal spines and 7–8 soft rays, over 26 vertebrae. The species' two most useful field marks are colour-pattern features. The first is the 'black cap': the supraorbital stripe is diffuse and expanded into a dark area covering the top of the head, running up from the lower lip across the front of the eye and back toward the dorsal-fin origin, so that the fish appears to wear a dusky hood. The second is a juvenile pattern of seven vertical dark bars; the middle bars (roughly the third through sixth from the head) are boldest in young and medium-sized fish but fade in adults, many of which retain only the third (mid-lateral) bar. Unlike Mazarunia mazarunii and Mazarunia pala, this species lacks a discrete mid-lateral spot and the infraorbital and supraorbital bars seen in the type species. In life it is more colourful than its muted preserved specimens suggest: the head below the eye is bright pink, yellow or orange, extending onto the gill cover and onto the body just behind it, and there is a vivid orange blotch above the base of the pectoral fin; the iris is greenish with golden highlights, and the dorsal and anal fins shade from gray to maroon. Sexual dimorphism follows the dwarf-cichlid template — males develop a small nuchal hump in front of the first dorsal-fin spine and possibly longer dorsal- and anal-fin filaments, while ripe females are deeper-bodied — though the published description emphasises osteology and meristics over external sexual characters.
Habitat
Like every member of its genus, Mazarunia charadrica is found nowhere on Earth but the upper Mazaruni River drainage, a headwater system of the Essequibo basin in the Cuyuni-Mazaruni region of western Guyana. It is, however, the most widely distributed of the three Mazarunia: it is known from the upper Mazaruni main channel, its direct tributaries the Kamarang and Kukui rivers, Abbou Creek, and several tributaries of the Kako River including Waruma, Sandaa and Paikwa creeks, and the describers expect it to occur in essentially all upper-Mazaruni tributaries. What makes this range so striking is its isolation: the upper Mazaruni sits on a highland plateau of the Pakaraima Mountains, ringed by rapids and falls and hydrogeographically cut off from the rest of the Essequibo, and it supports one of the highest proportions of endemic freshwater fishes of any river fauna in the Neotropics — most of its species occur in no other river. Within this 'lost world,' Mazarunia charadrica is the most reophilic (current-loving) of its genus. While it can be collected alongside its congeners in sandy main-channel sites with sluggish flow, it is most abundant in steep tributaries with rocky substrates and abundant rapids — the torrent habitats its name commemorates. The water it lives in is among the softest and most acidic any cichlid inhabits: field measurements from the type series record blackwater of fairly high transparency (2–3 ft Secchi depth), currents from still to about 2 ft/s, temperatures of roughly 71–76 °F, a pH of just 4.4–4.8, dissolved oxygen of 5.2–9.3 mg/L, and an extraordinarily low conductivity below 10 µS — a nutrient-poor, ion-poor, tannin-stained highland stream.
Feeding
No dedicated dietary study of Mazarunia charadrica has been published — the species has been collected and described far more than it has been observed feeding — but its anatomy and relationships mark it as a benthic invertivore. FishBase's model places it at a trophic level near 3.2, the value typical of a small carnivore that works the bottom and the surfaces of stones and wood for aquatic insect larvae, micro-crustaceans and other small invertebrates rather than rasping algae or, like the larger eartheaters Geophagus and Satanoperca, taking and winnowing mouthfuls of sand. Its subterminal mouth is consistent with picking prey from the substrate. In the clear-to-blackwater, rapid-strewn tributaries it favours, the available menu is dominated by the larvae of midges, mayflies, blackflies and other rheophilic stream insects that cling to rocks in flowing water — the staple of most small Guiana-Shield stream fishes — and the species can be assumed to forage opportunistically among the rocks, crevices and leaf litter of the streambed. In the impoverished waters of the upper Mazaruni, where dissolved nutrients are very low, this invertebrate-gleaning niche is the one that supports the bulk of the small fish fauna.
Mating
The courtship and pair-forming behaviour of Mazarunia charadrica has not been documented in the wild or in captivity; what can be said is extrapolated from its body plan, its placement among the biparental Geophagini, and observations of its better-studied relatives. As a small substrate-spawning cichlid it almost certainly forms a pair bond around a defended site rather than holding a harem or aggregating to spawn, with both partners participating in territory defence. At dwarf-cichlid size, territorial disputes are correspondingly modest in scale, contested over a patch of rocky streambed rather than a large arena, and the genus is not regarded as strongly aggressive. The vivid pink-and-orange head colours that emerge in life are the kind of signal that typically intensifies during courtship and pair maintenance in such fishes, but because Mazarunia charadrica has essentially never been the subject of a behavioural study — wild or aquarium — the specifics of its colour signalling, pair formation and the division of labour between the sexes remain undescribed and are best treated as open questions rather than asserted detail.
Breeding
Mazarunia charadrica is, on the evidence of its anatomy and its relatives, a biparental substrate spawner rather than a mouthbrooder — eggs are laid on a sheltered surface, guarded and fanned by the parents, and the hatched larvae moved to protective cavities or crevices where the pair continues to tend them. For the type species Mazarunia mazarunii, the one consistently reported reproductive detail is that both parents guard the clutch and deposit the larvae in small holes among submerged roots, and Mazarunia charadrica can reasonably be expected to follow the same general pattern, adapted to the rockier, faster habitats it prefers. Beyond that, the specifics are genuinely undocumented: no clutch count, incubation time or fry-development sequence has been published for this species. As a fish reaching about 3 in it would lay a small clutch in keeping with its size; genus-typical and family-typical figures for dwarf substrate spawners of this kind run on the order of a few dozen to perhaps a hundred or so eggs per spawn rather than the hundreds or thousands of a large eartheater. Parental care is presumably biparental and extended through the free-swimming fry stage. The honest summary is that the reproductive biology of Mazarunia charadrica has not been formally described — a reflection of how little this remote endemic has been studied in life.
In the aquarium
Mazarunia charadrica is, in practical terms, not an aquarium fish: it is a remote single-drainage endemic that has essentially never entered the ornamental trade, and there is no body of documented aquarium experience to draw on. Anything written about keeping it is therefore extrapolation from its biotope and its relatives, and any specimen that did reach a hobbyist should be regarded as a conservation-minded specialist project, not a fish to be sought out casually from the wild given its Vulnerable status and tiny range.
Were it kept, the central challenge would be water chemistry. This species lives in some of the softest, most acidic water tolerated by any cichlid — a recorded pH of 4.4–4.8 and conductivity below 10 µS — conditions that are difficult to create and to hold stable in a closed system and that demand reverse-osmosis or rainwater heavily blackened with peat, leaf litter and botanicals, with little or no buffering. Temperature should sit on the cool side for a tropical fish, around the low-to-mid 20s °C (its wild range is roughly 71–76 °F), and because it is the most reophilic of its genus it would appreciate a brisk, well-oxygenated current over a substrate of sand, rounded stones and leaf litter, with rockwork providing the crevices it uses for shelter and presumably for spawning.
Because adults top out near 3 in, a modest footprint — on the order of 31.5 in of tank length for a pair — would be ample, and a species or quiet blackwater-biotope setup is far wiser than a busy community. Small live and frozen foods (bloodworm, daphnia, micro-crustaceans, baby brine shrimp) suit a small benthic invertivore. The realistic bottom line is that this is a fish to admire in its native streams and in the literature rather than one with an established place in the hobby; husbandry guidance here is necessarily inferred, and prospective keepers should weigh its rarity and protected, fragile habitat before contemplating it at all.
Conservation
The IUCN Red List assesses Mazarunia charadrica as Vulnerable (VU) under criterion B1ab(iii), in an assessment by D.C. Taphorn and D. Rodríguez-Olarte dated 1 November 2023 and published in 2024; the population trend is recorded as unknown. The listing reflects the fish's small, single-drainage range — an estimated extent of occurrence of roughly 2,283–11,101 mi² confined to the upper Mazaruni and limited to about six threat-based locations — rather than any measured decline; there is no assessment of current population numbers. The dominant threat the assessors name is gold mining: extensive, largely illegal open-pit and river-dredge gold (and diamond) mining in the upper Mazaruni degrades aquatic habitat, increasing siltation, turbidity and contamination in exactly the clear, rocky, blackwater streams this species depends on, and the basin currently has no formal protection from this or from deforestation for agriculture. Human population numbers in the region are low but steadily increasing. These pressures are the same ones that hang over the wider upper-Mazaruni 'lost world' fauna, whose exceptionally high endemism makes it disproportionately vulnerable to biodiversity loss for its small area. Researchers including López-Fernández and Taphorn have repeatedly urged formal protection — a reserve or national park, regulated mining, controls on deforestation and flow alteration, and prevention of non-native fish introductions — to safeguard a fauna in which the great majority of species, this little cichlid among them, exist nowhere else on Earth.