Taxonomy & naming
Satanoperca rhynchitis was described by the Swedish ichthyologist Sven O. Kullander in 2012, in a taxonomic review of the French Guianan Satanoperca published in the journal Cybium (36(1): 247–262). The holotype, an adult male of 4 in standard length catalogued as IRSNB 881 at the Royal Belgian Institute of Natural Sciences, was collected in 1969 by Léopold III and J.-P. Gosse from Crique Sikini, a left-bank tributary of the Oyapock River; paratype series are held at IRSNB, the Muséum national d'Histoire naturelle (MNHN), the Swedish Museum of Natural History (NRM) and the former Zoölogisch Museum Amsterdam (ZMA). The species belongs to the eartheater subfamily Geophaginae (treated as Cichlinae in some classifications) and falls within the Satanoperca jurupari species group — the mouthbrooding lineage of the genus, as distinct from the substrate-spawning Satanoperca daemon and Satanoperca acuticeps groups. Before Kullander's work it was lumped under Satanoperca jurupari and circulated in the hobby as Satanoperca sp. 'red lips'. Diagnosis rests on a combination of characters: red lips in live adults, the absence of dark lateral blotches or bands, the absence of white spots on the head, fewer soft dorsal-fin rays (8–10, modally 9, versus 12–14 in some congeners), 25–27 (modally 26) scales in the E1 row, and 12–14 ceratobranchial gill-rakers. Its closest relative is Satanoperca jurupari itself, from which it differs in modal fin counts, a narrower gill blade, and a markedly longer snout. The picture is not entirely tidy: red-lipped fish from the Rio Araguari in adjacent Amapá, Brazil, are morphologically intermediate between rhynchitis and jurupari and were not recovered as genetically distinct, leaving open whether the Guianan form is a full species, a clinal extreme, a rheophilic phenotype, or part of a single Satanoperca jurupari meta-population.
Morphology
This is a relatively modest-sized eartheater. FishBase gives a maximum of 5.5 in standard length, and Kullander's series and the hobby literature place adults at roughly 5–5.5 in SL — smaller than the larger demonfishes of the Satanoperca daemon group. The body is short and fairly deep, with the high-set eye, sloping forehead and protrusible, ventrally-directed mouth typical of the genus. Coloration is restrained: a tan to greyish-silver ground with iridescent flecking, lacking the bold dark lateral blotches of the Satanoperca daemon group and the dark mid-lateral band or row of spots seen in some jurupari-group populations. As in all Satanoperca, a small ocellated (eye-like) spot sits at the upper base of the caudal fin — the single feature that separates the genus from all other geophagines. The species' signature is its snout, which is proportionally longer than in any close relative (14.3–19.4% of standard length, versus 11.3–15.9% in Satanoperca jurupari); the specific name rhynchitis derives directly from this trait. Live adults develop reddish lips, the character behind the old trade name 'red lips'. Meristics recorded by Kullander include 14–16 dorsal spines, 9–10 (modally 9) soft dorsal rays and 27–28 vertebrae. Sexual dimorphism is slight: females tend to grow a little smaller than males and become noticeably deeper-bodied when gravid, but the sexes are otherwise difficult to tell apart.
Habitat
Satanoperca rhynchitis is endemic to French Guiana, recorded only from the Oyapock (Oiapoque), Approuague (including the Kaw), Kourou, Comté, Iracoubo and Sinnamary river drainages along the country's coastal slope; Eschmeyer's Catalog of Fishes extends the documented range marginally into adjacent Brazil, reflecting the intermediate Amapá populations. More than ninety percent of French Guiana is tropical rainforest, with a year-round warm climate and two wet seasons (roughly December–February and April–June) during which river levels, flow and turbidity rise sharply. Kullander noted that the Oyapock is rich in rapids and suggested that the species' elongated snout may be an adaptation to faster-flowing water — a habitat departure from the still, slow blackwaters where most jurupari-group eartheaters live. In-situ chemistry has not been formally published for this species, but the Guianan coastal rivers it occupies are generally warm, soft and slightly acidic to near-neutral. Hobby and field sources converge on a temperature range of about 72–82 °F, a pH around 5.5–7.5 and soft to moderately soft water (roughly 36–215 ppm total hardness). Recorded depths for the species are not documented, consistent with a shallow-water stream and river-margin fish.
Feeding
Like all members of its genus, Satanoperca rhynchitis is a benthophagous sand-sifter — the behaviour that earns the group the common name 'eartheater'. It takes mouthfuls of sand and fine sediment, sorts edible particles in the buccal cavity and pharynx, and expels the cleaned substrate through the gill openings and mouth. FishBase places it at a trophic level of about 3.1, consistent with a micro-invertebrate-and-detritus diet rather than predation. Stomach-content data reported for the species comprise small aquatic and terrestrial invertebrates — cladocerans, ostracods and insect larvae, chironomid (midge) larvae prominent among them — together with plant material such as seeds, organic detritus and ingested sediment. Even large adults appear unable to handle large prey, so in the wild it functions as a fine-particle forager of the sandy stream bed, processing the soft-sediment layer for the small invertebrates and organic matter living within it. Once settled it will readily rise into the water column to intercept drifting food before returning to browse the bottom.
Mating
Outside of breeding, Satanoperca rhynchitis is gregarious and notably peaceful, living in loose aggregations; juveniles in particular show strong shoaling instincts, and groups establish a clear dominance hierarchy rather than fragmenting into rigid territories. Reproduction reorganises this social structure around temporary pair territories. Courtship is initiated by the male, with prospective breeders establishing a defended area typically centred on a piece of driftwood or other solid object on the sand. A gravid female is courted, and once a pair forms the two may jointly hold the territory for a few days before spawning, excluding other fishes — conspecifics above all — from the vicinity. Because the sexes are so similar and maturity is slow (often a year or two), pairs are usually best allowed to form naturally from a group of young fish rather than hand-selected. The strong intra-group antagonism that can appear when these fish are kept in small numbers is the social flip-side of an otherwise mild temperament.
Breeding
Satanoperca rhynchitis is an ovophilous (immediate) maternal mouthbrooder, the reproductive mode characteristic of the Satanoperca jurupari group and in clear contrast to the substrate-spawning Satanoperca daemon and Satanoperca acuticeps groups. Spawning has been achieved in aquaria. There is no single obvious trigger; the conditions that bring fish into breeding are simply a good, varied diet and a stringent maintenance regime built around large, frequent water changes. The pair clears and defends a small site, and the female deposits eggs in small batches; immediately after fertilisation she takes them up into her mouth, repeating the cycle until she is brooding several hundred eggs. In some spawnings the male picks up a portion of the eggs but does not usually hold them for long, and the female is typically driven from the territory once spawning is complete — though some males reportedly show extended brood care. The female incubates the developing eggs and larvae buccally; once the fry are released and free-swimming they are easily reared, taking fine powdered foods, Artemia nauplii and microworm. A precise wild clutch figure has not been published, but the genus-typical 'several hundred eggs' is the working estimate. In a community tank, brooding females are best isolated, as released fry are quickly eaten by other fishes, including their own kind.
In the aquarium
Satanoperca rhynchitis reaches the hobby only occasionally, usually as wild imports from French Guiana or as tank-bred fish under the old 'red lips' label, and it is a fish for the intermediate-to-experienced keeper rather than the beginner. Because it is gregarious and shoals, it should be kept in a group — five to eight individuals is a sensible minimum — which spreads aggression and lets the fish settle; kept in twos and threes, subordinate fish tend to be bullied and the group stays nervous. A group of this size needs a large footprint, with a base around 180 x 23.5 in (roughly 170 US gal) recommended.
The single most important feature of the tank is a soft, fine sand substrate deep enough for natural sifting. Gravel and small pebbles interfere with feeding, can damage the delicate gill filaments and may be swallowed; for a fish that processes the substrate through its gills all day, sand is non-negotiable. Décor is otherwise a matter of taste — subdued lighting, driftwood and scattered roots suit the species well. Leaf litter, though natural, is best avoided here because the constant sifting throws partly-decomposed material into suspension, clouding the water and clogging filters.
Water quality matters more than exact chemistry. These cichlids are highly sensitive to deteriorating conditions and to swings in parameters, and must never go into a biologically immature tank; inadequate maintenance shows up as head-and-lateral-line erosion or stunted growth. The standard approach is heavy biological and mechanical filtration (canister filters and/or a sump) combined with weekly water changes of 50–70 percent, with mechanical media chosen to trap the fine sand the fish stir up. Strong current should be avoided despite the species' rheophilic leanings — position returns to circulate without blasting the fish. Target temperature around 75–82 °F, pH about 5.5–7.5 trending toward the lower, softer end for breeding, and soft to moderately soft water.
Feeding is straightforward provided portions are fine-grade: small live or frozen bloodworm, Tubifex, Artemia and mosquito larvae alongside good sinking prepared foods, ideally some with a high vegetable (Spirulina) content. Several small feedings a day mimic natural browsing and give the best growth and condition. As tankmates, calm midwater and upper-level South Americans that share soft, warm water are ideal; avoid aggressive or territorial substrate-dwellers and anything needing hard, alkaline water. Freshwater stingrays (Potamotrygon) are sometimes combined with eartheaters but have, in some tanks, made the cichlids vanish overnight.
Conservation
The IUCN Red List assesses Satanoperca rhynchitis as Least Concern, in an assessment published in 2021 (assessed 17 January 2021) by Donald C. Taphorn and Douglas Rodríguez-Olarte. It carries no CITES or CMS listing and is rated harmless to humans. The species is naturally restricted to a small set of coastal drainages in French Guiana, a region whose rivers remain in comparatively good condition: more than ninety percent of the country is still under tropical rainforest, and human pressure on its aquatic systems is light by Amazonian standards. That narrow, single-country range is nonetheless worth noting — an endemic of a few rivers is intrinsically more exposed to localised disturbance (deforestation, gold-mining and its mercury contamination, and changes to flow regimes) than a basin-wide generalist would be. None of these is documented as a present threat to this particular cichlid, and its conservation outlook is currently secure, but its limited distribution is the context against which any future change should be read.