Taxonomy & naming
Satanoperca curupira was described in 2018 by Renata R. Ota, Sven O. Kullander, Gabriel C. Deprá, Weferson J. da Graça and Carla S. Pavanelli in Zootaxa 4379(1): 103–112, from material collected in the Rio Madeira basin in the State of Rondônia, southwestern Brazilian Amazon. The holotype is held at the Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura, Universidade Estadual de Maringá (NUP 13671), with paratypes distributed among INPA, MCP, MZUSP and NUP. The genus Satanoperca was erected by Albert Günther in 1862 for eartheaters split out of Geophagus; curupira is one of roughly a dozen valid species in it. Within that genus it belongs to the Satanoperca jurupari species-group — the lower-headed, finely lined 'demon eartheaters' as opposed to the big-blotched daemon/lilith group. The describers diagnosed it against all congeners by a combination of colour-pattern characters: three to seven dark-brown oblique stripes on the lacrimal (versus two well-defined stripes, or none, in other species) together with an irregular pattern of dark-brown stripes across the cheek and opercular (gill-cover) series, where other members of the group have either an unmarked cheek or light-beige rounded spots. The fish had been known to aquarists for years before it had a name: Uwe Werner collected it in Rondônia in 1996 and reported it in a 2004 DATZ article as 'Satanoperca sp. Jarú', after the Rio Jaru where some of his stock originated, and one of his field photographs was later used in the formal description.
Morphology
Satanoperca curupira is a moderately large eartheater. The largest type specimens measured roughly 6 in in standard length (snout to tail base), and wild adults that Werner collected ran about 6.5–7 in in total length, so it is a fish in the same size class as a typical Satanoperca jurupari rather than a giant. The body is the classic Satanoperca shape: laterally compressed and fairly deep, with a long, pointed snout, a terminal mouth with thick lips, and large eyes set high on the head so that the pupil sits at about the level of the upper lateral line — the geometry of a fish built to take mouthfuls of sand and scan the substrate. Ground colour is a yellowish-brown back fading to a yellowish-white belly, with a brownish head. The diagnostic feature is the 'face mask' of three to seven fine oblique red-brown lines on the lacrimal running from the upper lip toward the eye; these lines vary considerably between individuals — sometimes straight and parallel, sometimes broken into dots or worm-like vermiculations, and the cheeks and gill covers carry further irregular dark-brown striping. Across the flanks run about seven dark vertical bars, six descending from the dorsal-fin base and a seventh on the caudal peduncle, several of which can be incomplete, diffuse or Y-shaped. Unlike Satanoperca jurupari, the dark midlateral longitudinal band is barely visible or absent altogether. Sexual dimorphism is subtle: males grow slightly larger and carry longer, more pointed dorsal and anal fins, and in mature fish the male's ventral (pelvic) fins are noticeably longer than the female's — a difference Werner used to sex his breeders.
Habitat
The species is endemic to Brazil and, within it, restricted to the Rio Madeira basin — a far narrower range than the pan-Amazonian Satanoperca jurupari it lives alongside. It is recorded from the main channel of the Madeira and from several tributaries that drain the Brazilian Shield: the rios Jaciparaná, Jamari, Jaru and Machado, plus the Rio Roosevelt (a tributary of the Aripuanã) and the Rio São Luis (a tributary of the Guaporé). These are predominantly clear- and blackwater rivers and streams of the southern Amazon, draining ancient shield rock rather than the silty Andean whitewater of the Madeira's headwaters. Werner found it in small, fast-flowing rivers over sand, frequently in the company of Satanoperca jurupari, the two species genuinely syntopic — netted together in the same stretches. The describers noted that its tightly bounded distribution mirrors that of several other Satanoperca species, which tend to be basin endemics rather than wide-ranging generalists. In-situ water chemistry has not been formally published for the species, but the clear/blackwater shield streams it inhabits are characteristically warm, soft and acidic, and aquarists who keep wild stock report it doing best in soft, acidic water — consistent with the broader Madeira-tributary habitat.
Feeding
Like all eartheaters of its group, Satanoperca curupira is a sand-sifting benthic invertivore. It takes mouthfuls of fine sediment, sorts edible items from grit inside the mouth and pharynx, and expels the cleaned sand through the gill openings and mouth — the winnowing technique that gives the geophagines their name. In the wild this yields a diet of small benthic invertebrates, insect larvae, micro-crustaceans and associated organic matter culled from the sand bed. The long snout, high-set eyes and protrusible jaws are all adaptations to this constant browsing of the substrate. In aquaria the species shows the same preference for fine foods and feeds somewhat fastidiously: Werner noted that his fish took even Mysis reluctantly but eagerly attacked smaller fare — Artemia, copepods, water fleas, grindal worms, bloodworms and finely chopped mussel — and also accepted flake and sinking sticks. As a sand-sifter it occupies the same bottom-foraging guild as Geophagus and the other Satanoperca it co-occurs with, partitioning the resource by microhabitat rather than diet.
Mating
Detailed reproductive behaviour comes chiefly from Werner's aquarium observations of wild-derived stock, since nothing has been published from the wild. Outside breeding the fish are peaceable and gregarious, and pair formation is undramatic — Werner saw no overt courtship displays, sparring or territorial confrontation before his fish spawned, the pair simply forming quietly within a group. Sexes are hard to separate until the fish are in condition, when the male's slightly greater size and distinctly longer ventral fins become apparent. When a pair does meet they greet one another with mild flank-nudging and gentle tail-beating rather than the ritualised aggression of substrate-spawning cichlids, and Werner found the species notably non-aggressive even in fairly confined quarters. This restrained social style is typical of the jurupari-group eartheaters, which invest in mouthbrooding rather than in defending a substrate nest, and which therefore have little need for the heavy territoriality seen in cave- and pit-spawning cichlids.
Breeding
Satanoperca curupira is an immediate (ovophilous) biparental mouthbrooder — the defining reproductive mode of the Satanoperca jurupari group, and the trait that most sets these eartheaters apart from substrate-spawning relatives. Spawning happens without warning and without any preliminary digging: the female lays small batches of eggs on a gently sloping stone surface while the pair circle, the male fertilises each batch, and the eggs are picked up into the mouth almost at once. Werner's fish produced only about five to seven snow-white, slightly oval eggs per batch over a spawning. Both parents brood: the female typically takes the eggs first and carries them more often and for longer overall, while the male takes turns at irregular intervals — in one spawning the female brooded alone for the first ten days, in another the partners alternated from the start. Brooding is hard to detect externally because the fish make almost no visible chewing motions; the only tell is an occasional bulging of the throat as the eggs are shuffled. The fry are first released at about twelve days; an initial brood numbered roughly 100–300 young, released briefly at first and instantly taken back into the parents' mouths at any disturbance, with both adults sharing the duty. During release the pair hover 6–8 in apart, heads lowered and fins spread with the spine-tips and fin margins flushed black, while the fry forage between them. Strikingly, both parents continue to feed while carrying — gently sucking in fine food past a half-closed mouth — and a brooding male may even release some or all of the fry through his gill slits to swallow a clump of mosquito larvae, then re-collect them. Free-swimming young take Artemia nauplii from the start and grow quickly; Werner kept his with the parents for about five weeks, the female still willing to shelter them late in that period.
In the aquarium
Satanoperca curupira is an uncommon but established aquarium fish, traded for years as 'Satanoperca sp. Jarú' before it was named and reaching hobbyists mainly as wild imports or their tank-raised offspring. It is a fish for the experienced eartheater keeper rather than a beginner. Because it stays active and reaches around 6 in, and because it is best kept as a small group from which pairs form, a long tank is needed — a footprint on the order of 59 in (about 90 US gal) or larger suits a group of four to six, in line with the 150-cm tank Werner used.
The single non-negotiable requirement is a deep bed of fine, soft sand. This is a dedicated sand-sifter that feeds by taking the substrate into its mouth; gravel prevents normal feeding and risks abrading the gills. Décor is otherwise simple — driftwood, leaf litter, a few smooth stones (which double as spawning sites) and subdued lighting all suit a fish of shaded shield-stream waters. Filtration should be generous and the tank biologically mature before the fish go in, as Satanoperca are sensitive to dissolved waste and prone to head-and-lateral-line erosion when water quality slips; large, regular water changes are the standard insurance.
Water should be warm, soft and acidic, mirroring the clear/blackwater Madeira tributaries: roughly 77–84 °F, pH about 5.5–7.0, and low hardness. The species tolerates a fairly wide pH band (hobby reports span pH 4.0–7.0), but for spawning Werner brought his water down to around 1 °dGH, 4–6 °dKH and pH 6.5 using ion-exchanged water and peat — soft, acidic conditions consistently improve breeding readiness. Feeding takes some care: these fish favour fine foods and can be fussy, so offer small frozen and live items (cyclops/copepods, daphnia, Artemia, grindal worms, bloodworm, finely chopped mussel) alongside good sinking granules and flake, and avoid large or hard-shelled foods.
Temperament is the species' great virtue and its quiet liability. It is peaceful, even toward conspecifics, which makes it an excellent community eartheater but a poor competitor: Werner found that smaller Geophagus proximus dominated his curupira at feeding time and bullied them off the food once the Geophagus were guarding fry, and even wild angelfish had to be chosen as gentler companions. Keep it with calm, similarly mannered South Americans — peaceful tetras and other characins, smaller or equally placid eartheaters, and other non-pushy cichlids — and avoid boisterous or food-aggressive tankmates that will outcompete it. As a relatively new fish in the hobby, much of its long-term care and breeding is still being worked out.
Conservation
Satanoperca curupira has not been evaluated for the IUCN Red List; there is no Red List assessment or category for the species, so its global conservation status is formally Not Evaluated. The original describers carried out a preliminary, internal assessment following IUCN guidelines as part of the description, but that is not a published Red List entry. The species' main vulnerability is intrinsic: unlike the wide-ranging Satanoperca jurupari, it is a Madeira-basin endemic with a comparatively restricted distribution, the pattern the describers noted for several Satanoperca species — and narrow-range endemics are inherently more exposed to localised habitat change. The Rio Madeira drainage faces real and accelerating pressures, including large hydroelectric dams on the Madeira itself (Santo Antônio and Jirau) and their alteration of the river's flow and sediment regime, plus deforestation and gold-mining with associated mercury contamination across Rondônia and the wider southern Amazon. None of these has been documented as a specific threat to this particular cichlid, but they form the backdrop against which the conservation of a restricted-range Madeira endemic should be read. It carries no CITES listing and is taken only in small numbers for the specialist aquarium trade.