Taxonomy & naming
Three Venezuelan ichthyologists — Jaime H. Hernández-Acevedo, Antonio Machado-Allison and Carlos A. Lasso — described Aequidens superomaculatum in 2015, in volume 16 of the journal Biota Colombiana. The genus Aequidens is much older, erected by Eigenmann and Bray in 1894 (first as a subgenus of Astronotus) for medium-sized South American 'acaras' with even-sized teeth; the name means 'equal teeth.' It was long a sprawling catch-all, and has since been pared back as many former members moved to genera such as Andinoacara, Bujurquina, Laetacara and Cleithracara. Aequidens superomaculatum sits in subfamily Cichlinae, tribe Cichlasomatini. Its describers separated it from close relatives by a bundle of characters: worm-line (vermiculated) markings on the cheek, snout and preopercle, a high vertebral count, an unbroken lateral stripe, and the feature the name commemorates — a dark lateral blotch carried high on both flanks. The epithet joins the Latin super, 'above,' to maculatum, 'spotted,' for that high-set mark. The type locality lies in Estado Amazonas, Venezuela, on the Río Casiquiare–Río Baria about three kilometres downstream of the La Neblina base camp, at the foot of the great Cerro de la Neblina massif. No junior synonyms are recognised.
Morphology
This is a moderately large acara. The type series reaches 5.5 in standard length — roughly 6.5 in total length — and the describers call it a moderately long species; the IUCN account puts the ceiling near 6.5 in total length. FishBase's listed 2.5 in SL reflects only the smallest measured specimen and badly understates the fish. The build is typical Aequidens: robust, moderately elongate and laterally compressed, its depth going about 2.3 times into the standard length, with a short snout and a large eye. Colour is what settles the identification. A complete, uninterrupted lateral band runs at every size — in many relatives the band is broken or segmented at the lateromedial spot — and a rounded-to-oval dark blotch sits high on each flank, touching the base of the spiny dorsal fin and set off from the lateral band by a single scale row. That high position is exactly what the name superomaculatum records. Fine vermiculations mark the cheek, snout and preopercle; the juvenile suborbital bar fades by about 1 in SL, and the vertebral count is high (14+13=27), one of the traits allying it with the Aequidens pallidus group. In life the facial vermiculations glow an iridescent blue-green, and the body is a warm pale brown with yellow-ochre highlights around the lateral blotch — the colour that drew hobbyist attention before the fish had a scientific name. The 2015 description worked from unsexed material and records no sexual dimorphism.
Habitat
Aequidens superomaculatum lives in the blackwater rivers of southern Venezuela: the Casiquiare Canal drainage and the upper reaches of the Orinoco and Río Negro. The Casiquiare is the celebrated natural channel that ties the Orinoco to the Amazon system through the Negro, making this one of the few places on Earth where two great river basins stay continuously connected. The type locality is on the Río Baria near its junction with the Casiquiare, at the base of Cerro de la Neblina (around 0°53′N 66°00′W) in Venezuela's Amazonas state. These are warm, lowland, generally acidic and nutrient-poor blackwaters draining the Guiana Shield and the upper Orinoco–Negro lowlands. The IUCN assessment records the fish specifically from black-water rivers of just 4.6–5 µS/cm conductivity (after Brewer-Carías 1988) — water about as ion-poor as fresh water gets, the soft, dark, tannin-stained chemistry of the upper Negro and Casiquiare. The type series came from shallow river margins and from a pool joined to the main channel: the calm, shallow blackwater — on the order of 0–7 ft — where small acaras live. The 2015 description tabulated no temperature, pH or depth, so the warm, acidic figures given here are basin-typical rather than measured for the species.
Feeding
No dedicated dietary study has been published for Aequidens superomaculatum. Judging by the consistent ecology of the genus, it should be a small benthic omnivore — working over the substrate and through leaf litter and structure for aquatic insect larvae, micro-crustaceans and other small invertebrates, and taking detritus, algae and plant matter as well. Its blackwater haunts are nutrient-poor and often thick with sunken leaves and wood, exactly the setting where a small acara picks invertebrates off the bottom and out of decaying vegetation rather than chasing food in open water. This is a portrait drawn from the genus and the habitat, not from gut-content data for the species itself.
Mating
Courtship has not been described for Aequidens superomaculatum, but Aequidens are uniformly monogamous, pair-bonding, biparental substrate spawners, and this species is expected to follow suit. A pair forms and holds a shared territory, cleans a spawning surface — a flat stone, a submerged leaf, a firm patch of bottom — and courts with lateral displays, spread fins and heightened colour, the facial vermiculations and body tones brightening in a fish in condition. As in many small acaras, the sexes are probably much alike outside of breeding, told apart mainly by subtle differences in size and finnage and by the female's behaviour and shape when she is ready to spawn.
Breeding
No account of spawning, clutch size or fry development has been published for Aequidens superomaculatum specifically. By the consistent biology of the genus, it is an open, biparental substrate spawner: adhesive eggs are laid on a cleaned firm surface and tended by both parents — the female fanning and guarding the clutch, the male holding the territory — with the larvae shifted to pits after hatching and the free-swimming fry herded and protected as a school by both adults. Plenty of Aequidens breed in aquaria on exactly this template, and the hobbyist interest in the 'Casiquiare' acara that this fish represents makes captive spawning plausible. Even so, the specifics for Aequidens superomaculatum remain undocumented, and everything described here is inferred from the genus rather than recorded for the species.
In the aquarium
Aequidens superomaculatum had a place in the hobby before it had a name: fish from the Río Casiquiare on the Venezuela–Colombia frontier sold as an unnamed Aequidens — the 'Casiquiare acara' — well before the 2015 description, and material identified as this species has turned up in the specialist trade since. It stays an uncommon, somewhat specialist import rather than a staple, and well-tested husbandry literature is thin; the guidance below leans on the genus and on its blackwater origins.
Tank: a medium-sized acara of perhaps 5 in SL (around 6.5 in total length) wants a roomy planted or biotope-style setup with open swimming space, soft substrate, leaf litter and wood.
Water: its native rivers are warm, soft and acidic blackwater, so soft, gently acidic, well-filtered water with some tannin staining best reflects where it comes from — and the blue-green facial vermiculations show best over a dark substrate.
Diet: a varied omnivore menu of small frozen and live invertebrates, quality micro-pellets or flake, and some plant matter suits it.
Tankmates: like most acaras it is fairly peaceful for a cichlid outside breeding and mixes with similarly sized soft-water community fish, turning territorial once a pair spawns.
The honest framing is that this is a desirable but only intermittently available blackwater acara, best approached as a soft-water specialist's fish.
Conservation
The IUCN Red List assesses Aequidens superomaculatum as Least Concern (assessed 22 October 2020 by L. Mesa-Salazar, reviewed by D.C. Taphorn, published 2022). The reasoning is geographic: the fish is confined to the remote Casiquiare region, but its estimated area of occupancy (8,85 mi²) and extent of occurrence (35,305 mi²) are far too large for a threatened listing. It carries no CITES listing, and the assessors note it is unknown whether the species enters the ornamental trade. It also falls within the Alto Orinoco–Casiquiare Biosphere Reserve, which takes in the Parima-Tapirapecó and Serranía La Neblina national parks — protection that shields it from habitat loss far more than the narrow-range Brazilian endemics of its genus enjoy. The threats the assessment flags are real but indirect: deforestation, habitat transformation and mercury pollution from illegal gold mining across the upper Orinoco–Negro region. Population size and trend are unknown, and the species' true range and abundance within this little-surveyed wilderness are still incompletely documented.