Taxonomy & naming
Otocinclus mangaba was formally described by Lehmann A., Mayer, and Reis in 2010 in Copeia (volume 2010, number 4, pages 635–639), from specimens collected at Igarapé do Vinte e Dois, a small creek approximately 12 mi west of Humaitá toward Lábrea in the state of Amazonas, Brazil. The type locality coordinates are 7°35'36''S, 63°10'27''W within the Rio Madeira drainage.
The Catalog of Fishes (Eschmeyer, CAS) recognises Otocinclus mangaba as a valid species. It is placed in the subfamily Hypoptopomatinae within Loricariidae, the armoured suckermouth catfishes. Otocinclus is a large Neotropical genus of diminutive algae-grazing plecos, and O. mangaba can be distinguished from all congeners by a combination of characters: the absence of median abdominal plates between the lateral abdominal plates, and a dark spot at the base of the caudal fin that is separated from the midlateral stripe by an unpigmented area and does not extend posteriorly onto the middle caudal-fin rays.
Morphology
Adults of Otocinclus mangaba are very small, reaching a maximum of 1 in standard length (SL) — among the tiniest members of an already small-bodied genus. The body is elongated and slender, with the typical loricariid armour of bony scutes and a ventrally placed sucker mouth. Meristic counts recorded from the type series are: dorsal spines 2, dorsal soft rays 7, anal soft rays 6, and 22–23 vertebrae.
The diagnostic pigmentation consists of a dark midlateral stripe along the flanks and a distinct dark spot at the base of the caudal fin; these two markings are separated by a pale, unpigmented gap — a character shared with no other Otocinclus at the time of description. The caudal spot does not bleed posteriorly onto the caudal-fin rays themselves. Abdominal plating is reduced: median plates between the lateral abdominal plate rows are absent.
Sexual dimorphism follows the general Otocinclus pattern. Females are typically larger and noticeably broader in the abdominal region than males when viewed from above, particularly when gravid. Like other genus members, O. mangaba is capable of facultative air-breathing.
Habitat
The known range of Otocinclus mangaba is restricted to the Rio Madeira drainage in the state of Amazonas, Brazil. The type locality is Igarapé do Vinte e Dois, a small creek system west of Humaitá — a region characterised by lowland Amazonian forest with blackwater and clearwater tributary systems.
Like other otos, O. mangaba is a demersal fish of shallow, vegetated or algae-covered environments. Small Otocinclus typically occupy the surfaces of submerged leaves, rocks, and woody debris in areas with moderate to low current, where soft algae and biofilm accumulate. Detailed water chemistry data from the type locality are not available in the published record, but the broader Madeira system ranges from warm, slightly acidic clearwater to nutrient-moderate whitewater conditions in its lower reaches.
Feeding
Otocinclus mangaba is an aufwuchs micro-grazer — a forager of soft algae, biofilm, diatoms, and fine organic matter scraped from hard surfaces with its sucker mouth. This feeding mode is shared by the entire genus and is the reason otos are prized in planted aquaria for controlling soft green algae and diatom films without damaging plant leaves.
In captivity, O. mangaba and its congeners require a tank with well-established algae growth or regular supplemental feeding with algae-based foods. Algae wafers, spirulina tablets, and blanched vegetables such as courgette (zucchini) and cucumber are all accepted. The species is not suited to a bare, recently established aquarium where biofilm has not yet developed.
Mating
Specific courtship observations for Otocinclus mangaba are not documented in the published literature or in the hobby record. Based on the well-studied behaviour of congeners such as O. affinis and O. vittatus, the genus engages in active chase-based courtship, with males pursuing females and initiating spawning contact by pressing alongside or beneath the female. No nesting or territory-guarding behaviour is reported in Otocinclus; spawning is a brief, open affair.
Gravid females are distinguishable by their noticeably wider body profile, visible from above.
Breeding
No breeding reports for Otocinclus mangaba are on record at PlanetCatfish or in the aquarium literature. Given the extreme rarity of this species in the trade, captive spawning data are unavailable.
For context from the better-documented congeners: Otocinclus species are egg-scatterers that deposit adhesive eggs singly or in small clusters on plant leaves, glass, or smooth surfaces. Eggs hatch in a few days at tropical temperatures; fry are tiny at emergence and require very fine algae-based food. No parental care is provided. Water temperature, condition, and a high-quality diet are the principal triggers for spawning in the genus.
In the aquarium
Otocinclus mangaba is essentially absent from the ornamental trade; no sightings or keepers are registered on PlanetCatfish and the species is not commercially collected. Any care notes must therefore be extrapolated from congeners.
All Otocinclus are sensitive fish best kept in stable, mature aquaria with established biofilm and algae growth. They should be kept in groups — a minimum of six individuals is often recommended — as they are shoaling animals that show visible stress when isolated. Mortality during acclimatisation is the primary challenge with otos; newly imported specimens should be introduced only into well-cycled tanks and given a period of low disturbance.
Given the sub-1 in size of O. mangaba, tankmates should be small and non-aggressive. Suitable companions include small tetras, rasboras, and other peaceful micro-fish. Soft, slightly acidic to neutral water reflecting Amazonian conditions is appropriate. Supplemental feeding with algae-based wafers is essential if the tank does not sustain natural algae growth.
Conservation
The IUCN Red List assessed Otocinclus mangaba as Data Deficient (DD), last evaluated in November 2018. This reflects genuine gaps in knowledge rather than confirmed population decline: the species is known from a single type locality in the Rio Madeira drainage of Amazonas, Brazil, and its broader distribution, population size, and trends are unknown.
The Rio Madeira drainage has experienced substantial anthropogenic pressure, including large-scale hydroelectric development (the Santo Antônio and Jirau dams), sedimentation from deforestation and agricultural expansion, and mercury contamination from artisanal gold mining. The degree to which these pressures affect small creek habitats where O. mangaba may occur is not assessed. A targeted survey to determine its actual range and abundance would be the prerequisite for any meaningful conservation evaluation.