Taxonomy & naming
Geophagus neambi was described by Paulo H. F. Lucinda, Carlos A. S. de Lucena and Náthia C. Assis in 2010, in a Zootaxa paper (No. 2429) that simultaneously introduced a second Tocantins eartheater, Geophagus sveni. The holotype (MCP 43670, in the fish collection of the Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre) was taken at the Lajeado Hydroelectric Reservoir near Porto Nacional, Tocantins state, at 10°41'36"S, 48°24'52"W on the Rio Tocantins; paratypes are held at MCP and at the Universidade Federal do Tocantins (UNT). The Catalog of Fishes lists the name as valid, placing it in subfamily Cichlinae. Within Geophagus — the genus Heckel erected in 1840 and which Sven Kullander restricted in 1986 to the true sand-sifters with paired caudal extensions of the swim bladder — Geophagus neambi belongs to the putative Geophagus surinamensis species group, an assemblage of deep-bodied eartheaters carrying a dark mid-flank blotch. The describers separated it from its close relatives by a distinctive flank pattern of eight or nine narrow vertical bars that fork (bifurcate) above and below the lateral spot, the spot itself sitting in roughly the fourth bar. It had been known to hobbyists well before its formal description, traded as Geophagus sp. 'Tocantins' and Geophagus sp. 'rio Areões', the latter referring to an indigenous reserve in the Rio das Mortes drainage; aquarium specimens under those labels were later confirmed as Geophagus neambi by co-author Lucinda.
Morphology
Geophagus neambi is a moderately large, deep-bodied eartheater. FishBase records a maximum of about 8 in standard length in males and 7.5 in in females, with a published weight near 374 g; in practice most specimens are smaller, and Seriously Fish gives a working maximum of 6.5–8 in SL. The body shape is typical of the surinamensis group: laterally compressed, with a steep forehead and the protrusible, downturned mouth of a benthic sifter. Living fish are a warm tan to golden-olive, the flanks scored with fine horizontal rows of iridescent blue-green to orange spots and streaks — the anterior parts of those stripes running slightly more orange than the rear. A single dark blotch marks the middle of each side. The most reliable diagnostic features are negative and patterned: Geophagus neambi lacks the dark preopercular spot and the complete infra-orbital (cheek) stripe seen in many congeners, and instead shows eight or nine vertical bars on each flank — usually visible only when the fish is stressed, spawning or preserved — with the bar carrying the lateral spot, and those behind it, forking above and below into a branched pattern. The caudal fin is brownish-red, peppered with blue iridescent spots that can merge into vertical streaks; breeding adults flush a bright orange across the chest. Externally the sexes look alike.
Habitat
The species is endemic to Brazil, restricted to the upper and middle Rio Tocantins basin in the country's central-north. It is recorded through the Tocantins mainstem in Tocantins state and into the Rio das Mortes drainage of the Araguaia system (a major Tocantins tributary) near Nova Xavantina, Mato Grosso, from which it is collected for the aquarium trade. All of this falls within the Tocantins-Araguaia freshwater ecoregion, a basin noted for very high fish endemism. Like other surinamensis-group eartheaters, Geophagus neambi favours gently sloping marginal zones with soft bottoms of bare sand or fine mud along shores and around islands, often with scattered rocks, submerged roots, branches and leaf litter nearby. A 2007 study of sandbank-dwelling fishes in the Tocantins drainage recorded the species (then misidentified as Geophagus altifrons) over open sand alongside Satanoperca jurupari, Exodon paradoxus, and a range of characins and small catfishes. These are warm, shallow-water fish of the river margins; FishBase classifies the species as demersal and tropical. Reported aquarium-relevant chemistry spans a temperature of about 75–90 °F and a pH from roughly 5.5 to 7.5 over soft to moderately mineralized water — consistent with the soft, warm, near-neutral to mildly acidic clear- and whitewater of the Tocantins margins.
Feeding
Geophagus neambi is a benthophagous sand-sifter, the feeding mode that earns the genus its common name 'eartheater'. It takes mouthfuls of substrate, sorts edible particles in the buccal cavity and pharyngeal apparatus, and expels the cleaned sand and silt through the gill openings and mouth. FishBase places it low on the food web, with an estimated trophic level near 2.3. The stomach contents of wild fish are dominated by small aquatic and terrestrial invertebrates, plant material such as seeds, organic detritus and ingested sediment — the diet of a bottom-grazing generalist rather than a predator. Once settled, the fish readily rise into the water column to intercept drifting food, but their default behaviour is patient browsing of the substrate, and even adults seem unable to handle large prey items. A soft, sandy bottom is therefore not décor but a functional requirement: it is the medium through which the fish feeds, and without it normal foraging behaviour and long-term condition both suffer.
Mating
Outside of breeding Geophagus neambi is a notably peaceful and gregarious cichlid that lives in loose aggregations, with juveniles in particular showing strong grouping instincts. Within a group a dominance hierarchy forms, and pairs emerge from it rather than being imposed. Because the sexes are externally identical, pairing is a slow, self-selected process — fish may need a year or more to reach maturity, and the reliable route to a compatible pair is to raise a group of five to eight and let bonds form naturally. Courtship is comparatively understated for a cichlid: fin-flaring, circling, mutual gaping and head-jerking displays, after which a forming pair selects and cleans a spawning site and begins to defend the immediate area against intruders. There is no dramatic colour change beyond the orange chest flush of ripe adults, and no elaborate territorial architecture; the pair's defended zone is modest and centred on the chosen surface.
Breeding
Geophagus neambi is a delayed, larvophilous biparental mouthbrooder — it spawns on a substrate in the manner of an open spawner, then takes the developing eggs or larvae into the mouth. A pair cleans a flat surface, typically a flattish rock, a piece of driftwood or even bare aquarium glass, and the female lays one or more rows of eggs that the male follows to fertilise, the sequence repeated over several hours. Maximum brood size is around 200 eggs. In most spawnings the female gathers the eggs into her mouth soon after fertilisation, while the male defends the surrounding territory, though on occasion both parents share holding from the start or the male drives the female off to brood alone. At about 77–82 °F the fry become free-swimming roughly 8 to 11 days after spawning, at which point the parents begin releasing them to forage and shepherding them back into the mouth at any sign of danger — a rapid flick of the ventral fins appears to serve as the recall signal. Care is frequently shared, the brood passed between parents (often in a substrate depression) on a near-daily basis, and as the fry grow they return to the mouth mainly at night while the defended territory expands. No special trigger is needed beyond good feeding and a stable maintenance regime with large, regular water changes; the free-swimming fry take powdered dry foods, Artemia nauplii and microworm readily.
In the aquarium
Geophagus neambi has been bred in aquaria on many occasions and, away from spawning, is one of the more peaceable larger eartheaters — it will not trouble any tankmate too large to be swallowed. It is, however, a group fish and a demanding one on water quality. Because it is gregarious and forms a hierarchy, it should be kept in a shoal of at least five to eight; in smaller numbers weaker individuals are bullied and the group tends to stay nervous and unsettled. A shoal of this size needs a long tank — a footprint of about 180 by 23.5 in (roughly 170 US gal) or larger is the realistic minimum.
The single most important furnishing is a soft, sandy substrate, deep enough for the fish to sift naturally. Gravel and pebbles inhibit feeding, can abrade or be drawn into the gill filaments, and may be swallowed with risk of internal damage; for a compulsive sifter, fine sand is non-negotiable. Décor is otherwise a matter of taste — dim lighting, driftwood, and scattered roots or branches suit the species, and a flat water-worn rock or two gives potential spawning sites. Leaf litter, though natural, tends to be torn up by the constant sifting and clouds the water, so most keepers omit it.
Water quality matters more than exact parameters. These cichlids are extremely sensitive to deteriorating conditions and to swings in chemistry, and should never go into a biologically immature tank; chronic neglect shows up as head-and-lateral-line erosion and stunted growth. The standard regime is heavy over-filtration (canister filters and/or a sump) combined with weekly water changes of 50 to 70 percent, with mechanical media tuned to trap the fine particles the fish stir up, and filter returns positioned to avoid strong flow — these are fish of calm river margins. A temperature of 79–86 °F and a pH around 6.0 to 7.0 in soft to moderately hard water suit it well; it tolerates a wider band (about 75–90 °F, pH 5.5 to 7.5) but does best mid-range. Feed several small portions a day of fine-grade prepared foods with a vegetable component plus live or frozen bloodworm, Tubifex, Artemia and mosquito larvae. Peaceful South American community fish make ideal companions; avoid hard-water species and aggressive substrate-dwellers. Some keepers house Geophagus with Potamotrygon stingrays, which usually works but has occasionally ended with eartheaters vanishing overnight.
Conservation
The IUCN Red List assesses Geophagus neambi as Least Concern (assessed 7 November 2018 by the Instituto Chico Mendes de Conservação da Biodiversidade, ICMBio; published 2022), with a population trend reported as stable. It carries no CITES or CMS listing and is harmless to humans. The Least Concern rating reflects a reasonably wide distribution through the upper and middle Tocantins and modest collection pressure for the ornamental trade rather than an absence of habitat change. That habitat change is in fact the defining feature of its range: the Rio Tocantins is among the most intensively dammed rivers in Amazonia, and the species' own type locality is the Lajeado (Luís Eduardo Magalhães) hydroelectric reservoir at Porto Nacional. Its range is bracketed and fragmented by large dams — Serra da Mesa and Lajeado upstream, Estreito and the massive Tucuruí complex downstream — which convert flowing, sand-margined river into still reservoir, block migratory routes, alter the flood pulse and sediment regime, and reshape the fish community. The Tocantins-Araguaia basin holds an exceptional level of endemism (well over a quarter of its fishes occur nowhere else), so basin-wide hydropower development is the principal long-term concern for its native ichthyofauna. None of this is documented as a present threat to Geophagus neambi specifically — as a sand-margin generalist it appears to persist in and around the reservoirs — but its conservation status is best read against the continuing transformation of its river rather than in isolation.