Taxonomy & naming
Parotocinclus polyochrus was described by Scott A. Schaefer in 1988. The Catalog of Fishes (Eschmeyer, CAS) recognises the valid combination Parotocinclus polyochrus Schaefer, 1988, and FishBase places it in subfamily Hypoptopomatinae within the family Loricariidae.
The genus Parotocinclus comprises numerous small loricariids distributed across South America, distinguished within the Hypoptopomatinae — the group of dwarf, biofilm-grazing armoured catfishes that also includes Otocinclus. The exact generic limits of Parotocinclus have long been regarded as provisional, the genus having historically served as a catch-all for hypoptopomatine species not assignable elsewhere, and several revisions have moved species in and out of it. No L-number is associated with this species; it is not a fixture of the ornamental trade and circulates, if at all, under its scientific name.
Morphology
Parotocinclus polyochrus is a very small loricariid, reaching about 1 in standard length. Like other members of the subfamily it carries the loricariid body armour of overlapping bony plates and a ventral suckermouth used for grazing and for clinging to surfaces in current.
Beyond its small size and typical hypoptopomatine form, detailed morphological and colour-pattern notes for this species are confined to the original description; no broadly accessible aquarium account documents its appearance further. No reliable account of sexual dimorphism in P. polyochrus has been published.
Habitat
The species is known from the upper Negro River (rio Negro) basin in South America. The Negro is the Amazon's largest blackwater tributary — its waters are stained tea-dark by dissolved tannins leached from flooded forest, typically very soft, ion-poor, and acidic, and low in dissolved nutrients.
As a demersal, tropical freshwater fish of this system, P. polyochrus is associated with the bottom and with submerged surfaces from which biofilm can be grazed. Precise microhabitat data — substrate, depth, current, and seasonal water chemistry at its collection sites — have not been published in accessible sources.
Feeding
Like other small hypoptopomatines, P. polyochrus is a grazer, rasping the thin film of algae, microorganisms, and fine detritus (aufwuchs) that coats submerged surfaces. FishBase records a low trophic level of roughly 2.4, consistent with a largely herbivorous, biofilm-based diet.
Facultative air-breathing has been reported for the genus Parotocinclus, an adaptation that allows these fish to supplement gill respiration in poorly oxygenated water. No species-specific feeding study for P. polyochrus has been published.
Mating
No data on courtship or mating behaviour have been published for Parotocinclus polyochrus.
Breeding
No breeding data — spawning mode, clutch size, or parental care — have been published for Parotocinclus polyochrus, in the wild or in captivity.
In the aquarium
Parotocinclus polyochrus is not an established aquarium species, and no husbandry record specific to it exists. General expectations can only be inferred from its biology and origin: as a small blackwater grazer of the upper Negro, it would require soft, acidic, warm water and a mature tank with abundant grazing surfaces (biofilm-covered wood, leaf litter, and rock). Any keeping recommendation beyond this would be speculation rather than documented practice, and the species should be regarded as one for which no reliable husbandry guidance is available.
Conservation
The IUCN Red List assessed Parotocinclus polyochrus as Least Concern (LC), with the assessment dated 7 August 2019. The category reflects no identified major threat at the time of assessment. The upper Negro basin remains comparatively intact relative to many Amazonian systems, though deforestation, mining, and watershed change are ongoing regional pressures across the broader Amazon.