Taxonomy & naming
Parotocinclus haroldoi was described by Garavello in 1988 in Naturalia (São Paulo) (volume 13, page 118, Figure 1), from specimens collected at the Córrego do Otaviano, Poço do Sanharó, Riacho Sanharó, Piauí, Brazil. No synonyms are recorded. The Catalog of Fishes (Eschmeyer, CAS) accepts Parotocinclus haroldoi Garavello, 1988 as the valid name.
The species epithet haroldoi is a patronym honouring Dr Heraldo Antônio Britski, one of Brazil's most distinguished freshwater ichthyologists. Britski received both his bachelor's degree (1960) and doctorate (1973) from the Universidade de São Paulo and spent his career at the Museu de Zoologia da USP, making foundational contributions to the systematics of Brazilian freshwater fishes across many families.
The genus Parotocinclus belongs to the subfamily Hypoptopomatinae. A key diagnostic character separating Parotocinclus from the closely related and superficially similar genus Otocinclus is the presence of an adipose fin in Parotocinclus — Otocinclus lacks this fin entirely. Schaefer (2003) provides the standard reference for subfamily-level systematics within Loricariidae.
Morphology
Parotocinclus haroldoi reaches a maximum of approximately 1.5 in standard length (SL) per FishBase (reference 81204); PlanetCatfish records 1 in SL for preserved specimens, consistent with this figure. The body is compact and armoured with the overlapping bony scutes typical of the Hypoptopomatinae, covering the dorsal and lateral surfaces.
The most useful field character separating P. haroldoi from Otocinclus species of similar size and appearance is the adipose fin, a small rounded fin positioned between the dorsal and caudal fins — present in Parotocinclus, consistently absent in Otocinclus. The mouth is disc-shaped and ventrally positioned, adapted for grazing on hard surfaces. Colouration is generally brownish or tan with darker markings.
Formal characterisation of sexual dimorphism in P. haroldoi is not available in the literature. As in other small hypoptopomatines, gravid females are likely broader-bodied when viewed from above.
Habitat
Parotocinclus haroldoi is known from river systems of Piauí State in northeastern Brazil, with the type locality at the Córrego do Otaviano — a small stream associated with the Riacho Sanharó drainage. The rivers of Piauí flow through the semi-arid to transitional zone between the Cerrado and Caatinga biomes, draining into the São Francisco system or the coastal rivers of the northeastern littoral.
Stream habitats in this region experience pronounced seasonality: a distinct dry season can reduce small streams to pools or isolated refugia, while the rainy season brings elevated flow and cooler water temperatures. The fish fauna of Piauí rivers is characterised by a high degree of endemism, and species such as P. haroldoi are known from geographically restricted areas.
Like other hypoptopomatines, P. haroldoi is demersal and closely associated with hard substrates — rocks, roots, and submerged wood — where biofilm and algae accumulate.
Feeding
Parotocinclus haroldoi is an algae and biofilm grazer with a trophic level of approximately 2.3. The disc-like rasping mouth is adapted for scraping aufwuchs from rock and wood surfaces — the community of algae, diatoms, cyanobacteria, and associated organic matter that forms a nutritious film on submerged hard substrates.
In captivity, the species should be maintained in a mature aquarium with natural biofilm on surfaces, supplemented with sinking algae wafers, spirulina-based foods, and blanched vegetables (courgette, cucumber). Competition for food with faster or more aggressive fish should be managed; small, gentle tankmates are most suitable.
Mating
No courtship or mating observations for Parotocinclus haroldoi have been documented in the published literature or hobby record. The genus Parotocinclus is rarely bred in captivity, and P. haroldoi in particular does not appear in breeding accounts on specialist catfish resources.
By inference from related small hypoptopomatines, active male pursuit and chasing of females is probable during the breeding season. Well-conditioned adults in a mature, stable aquarium with good water quality and varied diet would provide the most appropriate conditions for breeding attempts.
Breeding
Captive breeding of Parotocinclus haroldoi has not been reported. The species is not commonly kept in aquaria, limiting the opportunity for documented breeding observations.
Reproductive biology details — including egg deposition site, clutch size, incubation period, and parental care behaviour — are not available for this species. Based on general patterns within the subfamily, adhesive egg deposition on hard surfaces (glass, broad leaves, or smooth stone) is a reasonable expectation, but this remains unconfirmed.
In the aquarium
Parotocinclus haroldoi is an infrequently encountered species in the hobby, with a modest following among catfish specialists attracted by the diversity of the Hypoptopomatinae. Its small size (under 1.5 in SL) makes it manageable in modestly sized aquaria — a tank of 10–15 US gal with mature surfaces and gentle filtration would be appropriate for a small group.
The aquarium should provide flat stones, driftwood, and broad-leaved plants on which biofilm can establish. Water conditions should reflect the warm, seasonally variable rivers of Piauí: temperature 72–81 °F, soft to moderately hard, and slightly acidic to neutral pH. The species is not demanding in terms of water chemistry within this range, but stability and cleanliness are important for a fish of this small size.
Tankmates should be peaceful and non-competitive: small tetras, rasboras, and other small loricariids of similar temperament are suitable. The adipose fin — absent in Otocinclus but present in P. haroldoi — provides a reliable identification mark for aquarists comparing the two genera.
Conservation
The IUCN Red List assessed Parotocinclus haroldoi as Least Concern in November 2018. The species is restricted to river systems of Piauí State, northeastern Brazil, and its known range is geographically limited.
The semi-arid rivers of northeastern Brazil face significant pressures from water extraction for agriculture and human consumption, impoundment, riparian clearance, and the effects of prolonged drought exacerbated by climate variability. Small endemic fishes in isolated stream systems are inherently vulnerable to these pressures even where formal threat assessments do not yet reflect population declines. The Least Concern status should be viewed in the context of limited survey data from this region rather than confirmed abundance.