Taxonomy & naming
The French ichthyologist Jacques Pellegrin described this fish in 1902 as Acara geayi, from material collected on the Camopi River in French Guiana; the syntype series is held in the Muséum National d'Histoire Naturelle in Paris (MNHN 1901-0441 to 1901-0444, eight specimens, catalogued by Blanc in 1962). When the omnibus genus Acara was dismantled, geayi was shifted into Aequidens, the catch-all for South American acaras with three hard anal-fin rays, and for decades hobbyists and ichthyologists alike struggled to place it: imported into the American hobby in the late 1960s, it was variously sold as a Geophagus and even under the invalid name 'Geophagus thayeri'. Sven Kullander first proposed (1980) that it belonged not with the true Aequidens but near Acarichthys heckelii, and nine years later, in 1989, Kullander and Hans Nijssen erected the genus Guianacara — literally 'acará from the Guianas' — to receive it, designating geayi the type species alongside oelemariensis, owroewefi and sphenozona. That 1989 work, published as part of their monograph 'The Cichlids of Surinam' (co-authored with Han Nijssen), also split the new genus into two subgenera: Guianacara sensu stricto, holding geayi together with owroewefi and sphenozona, and Oelemaria, erected for the single species G. oelemariensis. Kullander's 1998 morphological analysis recovered Guianacara and Acarichthys as sister genera forming the tribe Acarichthyini within the eartheater subfamily Geophaginae, a relationship broadly (if not always cleanly) echoed by later molecular work (Farias et al. 1998; López-Fernández et al. 2005). The genus has since grown to include species described from Venezuela's Guiana Shield (Guianacara stergiosi and Guianacara cuyunii, López-Fernández, Taphorn & Kullander 2006; Guianacara dacrya, Arbour & López-Fernández 2011), with several undescribed forms still known from northeastern Brazil. Genuine Guianacara geayi is diagnosed within the genus by its wedge-shaped mid-lateral saddle spot with unusually large spots in the soft dorsal fin that extend onto the spiny portion as well, combined with the loss of black pigment on the anterior dorsal-fin membranes at adulthood (a juvenile character retained into maturity only by G. owroewefi and G. oelemariensis). It also holds a small piece of taxonomic trivia from before the genus existed: Kullander formally transferred the species into Acarichthys in 1980, a placement — following Regan's 1905 observation that it "falls in the genus Acara" close to what is now Acarichthys heckelii — it held for nine years until Guianacara was erected around it in 1989.
Morphology
Guianacara geayi is a moderately deep-bodied, laterally compressed cichlid with a notably straight to gently sloping forehead — a profile that, together with its sand-grubbing habits, long encouraged confusion with the true eartheaters. Weidner's field data on true wild Guianacara geayi (Approuague and Oyapock drainages) give adult males a total length up to about 8 in, with females running 1–1.5 in smaller; the widely repeated hobby figure of roughly 5 in almost certainly describes Guianacara sphenozona or another relative sold under the geayi name, since genuine geayi rarely reaches the trade. Bull males develop a blocky, somewhat humped head, and fish of either sex are reported to reach sexual maturity at a modest size. The ground colour is a muted yellowish-, pinkish- or beige-green overlain in places with rows of iridescent gold-scaled flecks, and the dorsal, anal and caudal fins carry light spotting. The defining mark of the genus is melanic: a dark vertical bar descends from the nape, passes through the eye (the supra- and infra-orbital bars) and reaches the lower margin of the gill cover, producing the masked, 'bandit' look — in geayi this suborbital element runs straight down to the lower edge of the operculum before kinking slightly upward again, leaving a small black angle on the cheek. A second dark sign — a wedge-shaped mid-lateral saddle spot, shared in form with the closely related Guianacara sphenozona — sits on the flank where the dorsal fin meets the body; the character that actually separates the two species is the soft dorsal fin, where geayi carries distinctly larger spots that extend onto the spiny portion of the fin as well as the soft rays, rather than being confined to the soft dorsal alone. Juveniles of both species retain dark pigment on the membranes of the front dorsal-fin spines, but this fades out in adult geayi (as in sphenozona); among the genus, only Guianacara owroewefi and G. oelemariensis keep the black anterior dorsal rays into adulthood. Sexual dimorphism is present but, per the original description, not strongly marked — males simply grow larger, with more pointed and elongated tips to the unpaired fins, somewhat more light spotting on those fins, and a less rounded ventral profile than females.
Habitat
The species is a Guiana Shield endemic of narrow range. The Catalog of Fishes and FishBase restrict it to the Approuague River drainage of French Guiana and the Oyapock River drainage shared by French Guiana and the Brazilian state of Amapá, with the type series from the Camopi, an Oyapock tributary — placing it within the FEOW 'Guianas' freshwater ecoregion, the network of independent rivers draining the northern and eastern Guiana Shield directly to the Atlantic. These are clear, soft, slightly acidic forest rivers rather than the silt-laden whitewaters of the Amazon. Guianacara geayi favours the calm waters of inland creeks, where it can be locally very abundant, and lingers over stony substrates along shallow banks; it also turns up directly in rapids and in the sheltered back-currents and slack eddies below them, sharing those fast, rocky stretches with loricariid catfishes and characins such as Leporinus despaxi and Parodon guyanensis, and — at one Approuague site — with numbers of the syntopic eartheater Geophagus camopiensis, netted in the same casts and usually outnumbered by Guianacara. Across the genus, López-Fernández and colleagues characterise the preferred biotope consistently: clear, soft, slightly acidic water over a substrate of large rocks interspersed with sandy patches, often where current is relatively brisk; field accounts add that softwater reaches with strong current, occasional rapids and rocky terrain are typical, while the calmer bays cut into the bank — with their sand, wood and leaf-litter deposits and eroded rock cavities — are favoured both as everyday shelter and as breeding sites. Typical aquarium-trade and field figures put the water at roughly pH 5.5–7.2 and 75–82 °F, very soft to moderately soft, though a rapids-margin site on the Approuague was recorded as warm as 90 °F and visibly turbid at the height of the wet season, showing the species tolerates considerably rougher conditions in the wild than the aquarium range implies. Because it is a fish of shallow rocky banks and creek margins, its documented depth band is shoreline-shallow, on the order of the upper metre or two of the water column.
Feeding
Like its eartheater relatives, Guianacara geayi works the bottom, taking mouthfuls of sand and fine sediment and winnowing out the edible fraction, and it readily digs pits and shifts substrate around rocks. Its diet is that of a benthic omnivore with a carnivorous lean: small benthic invertebrates — insect larvae, micro-crustaceans and other meiofauna sieved from sand and leaf litter — together with organic detritus and the aufwuchs scraped from stones along the banks it favours. FishBase places it at a trophic level near 3.3, consistent with a generalist invertivore rather than a strict herbivore or piscivore. In the rocky creek and cascade-margin habitats it occupies, it functions as one of several benthic foragers partitioning the sand-and-stone interface alongside loricariid catfishes and substrate-feeding characins.
Mating
Guianacara geayi is a harem-holding cave spawner: in the wild, mature fish gather along shallow rocky banks in groups led by a single dominant male attended by several females, each of which can establish her own small breeding territory centred on a crevice or cave. This polygynous structure, documented across the genus, means that outside of active spawning the fish are gregarious and comparatively peaceful — they are best kept and observed in groups rather than as isolated pairs. When a female ripens she selects and cleans a small cave or cleft and actively courts the male, who defends the wider territory. Marked size dimorphism shapes the spawning act itself: a large male may be physically too big to enter the female's chosen cave, in which case he fertilises the clutch from the entrance, beating milt inward with his fins rather than entering. Territorial disputes between rival males do occur but, given enough space and broken sightlines, rarely escalate to serious damage.
Breeding
Reproduction has been documented chiefly in aquaria; published wild spawning accounts are scarce. Guianacara geayi is a biparental cave (substrate) spawner with a strong female bias to brood care. Courtship, once a pair has formed and secured a well-protected home, involves the two circling nose to tail with all fins spread; spawning then takes place inside the cave, with the female attaching her eggs mainly to the vertical walls and only very rarely to the overhanging roof. The clutch is large for the fish's size — up to about 400 small (0.5 in), green-grey eggs, adhering along their long axis — and the male fertilises them, directly if he can enter or by spraying milt through the opening if he is too large. About four days after spawning the female frees the hatching larvae from their shells and gathers them onto the cave floor; over the following week the male repeatedly attempts to enter the breeding chamber but is never admitted. Rearing the resulting fry — up to roughly 250 in a good brood — is straightforward once they are free-swimming, since they take newly-hatched Artemia immediately and greedily, though growth is notably slow and the young take a long time to reach a saleable size; they themselves reach sexual maturity at around 3 in, at roughly 9–12 months old. Once released from the cave, the school of fry is led around the tank by both parents, whose contrast-rich breeding coloration is thought to help keep the shoal oriented and gathered. The species is regarded as relatively willing to spawn in captivity given suitable caves, soft slightly acidic water, and a settled harem.
In the aquarium
The bandit cichlid is a rewarding, manageable medium-sized cichlid that suits an aquarist ready to keep it as a group rather than a single pair. Because it is gregarious and only seasonally territorial, the standard advice is to keep six or more in a roomy tank — a footprint on the order of 47 in / 4 feet or larger comfortably houses a harem and lets subordinate fish stay out of a breeding female's way. The décor should reproduce its rocky-creek home: a soft sand substrate it can sift and dig (it will excavate pits and undermine loose rockwork, so bed stones on the tank bottom before adding sand), plenty of smooth rocks and driftwood arranged into caves and visual barriers, and at least one or two genuine spawning caves — an inverted terracotta flowerpot with the base knocked or chipped out is the classic choice. The trick Leibel describes is to size the cave entrance so the female can enter freely but a bull male — or a predator — cannot, the same 'hidey-hole' approach used for other size-dimorphic cave spawners. Live plants struggle against the constant digging and tend to be uprooted, so anchor or pot them or rely on hardscape.
Water should be soft and slightly acidic, around pH 5.5–7.2 and 75–82 °F, with hardness up to roughly 15 dH tolerated; the fish appreciates clean, well-oxygenated water and benefits from a mix of calm zones and areas of brisker current, which can be created with a powerhead and shelters from the flow. These are relatively peaceful, somewhat shy cichlids that nonetheless should not share a tank with fish small enough to be eaten or with overly boisterous tankmates; medium-sized, even-tempered South Americans of similar size make the best companions. Feeding is undemanding — they take quality flake, granules and cichlid pellets readily and colour up best on a varied menu of frozen and live foods such as bloodworm, white mosquito larvae, Mysis, brine shrimp and daphnia. The most common keeper error is one of identity rather than husbandry: most Guianacara sold as 'geayi' are actually Guianacara sphenozona (the western Guianas form) or one of the Venezuelan species — Ad Konings documented one such Venezuelan trade fish, sold as 'Red Cheek Geayi', and showed on geographic grounds that it could not be conspecific with the Suriname populations of the genus, an early record of just how far the trade name had drifted from the true species — since true Guianacara geayi comes from the rarely-collected rivers of French Guiana; their care, however, is essentially identical.
Conservation
The IUCN Red List assesses Guianacara geayi as Least Concern (assessed 18 November 2020 by R.G. Frederico, published 2023). The assessment notes no threats currently known to affect the species and lists its population trend as unknown, reflecting its occurrence in the comparatively intact, sparsely populated river systems of French Guiana and northern Amapá. It carries no CITES listing. That said, its global range is genuinely small — two adjacent Atlantic drainages on the eastern Guiana Shield — so it has less geographic buffer than the wide-ranging Amazonian cichlids, and the broader Guianas region faces localized pressures from artisanal and illegal gold mining (with attendant mercury contamination and sedimentation), deforestation and shifting land use. None of these is documented as a present danger to this particular fish, but a narrow-range endemic of clear forest rivers is exactly the kind of species whose status warrants periodic re-checking against those regional trends.