Taxonomy & naming
Parotocinclus longirostris was described by Julio Cesar Garavello in 1988 and is recognised as valid by the Catalog of Fishes (Eschmeyer, CAS), within the family Loricariidae, subfamily Hypoptopomatinae. The original combination is retained under the genus Parotocinclus.
The genus Parotocinclus comprises small loricariids closely related to the well-known dwarf grazers of the genus Otocinclus, from which they are distinguished by the presence of an adipose fin. The systematics of the Guyana-Shield Parotocinclus were treated by Schaefer and Provenzano (1993, Ichthyological Exploration of Freshwaters 4(1): 39–56), the principal reference for the regional fauna. The species has no L-number and no established English common name.
Morphology
Parotocinclus longirostris is among the smallest loricariids, reaching a maximum recorded length of about 1 in standard length (SL). It has the small, flattened, armour-plated body and ventral suckermouth typical of the dwarf Hypoptopomatinae, and — characteristic of the genus — retains an adipose fin.
The specific epithet longirostris is Latin for 'long-snouted', pointing to an elongate snout as a diagnostic feature relative to its congeners. Detailed coloration and meristic counts beyond the maximum length are not summarised in the cached references and are not reproduced here.
Habitat
The species occurs in South America in the Amazon River basin. It is a freshwater, demersal fish of tropical waters. Facultative air-breathing is reported for the genus Parotocinclus, an adaptation that allows these small fishes to tolerate the low-oxygen conditions of shallow, warm, vegetation-choked waters.
Specific microhabitat, current, and water-chemistry data for this species are not published in the cached sources. The small flattened body and suckermouth are consistent with life among leaf litter, marginal vegetation, and submerged wood, as is typical of the genus, but this is a genus-level inference rather than a measured account.
Feeding
No species-specific diet study is available, but the cached data give a trophic level of about 2.6, consistent with a largely herbivorous to omnivorous grazing habit. Small Parotocinclus typically rasp algae, biofilm, and fine detritus (aufwuchs) from submerged surfaces. A precise, documented diet for Parotocinclus longirostris is not recorded, so finer detail is left as no data published.
Mating
No mating or courtship behaviour has been documented for Parotocinclus longirostris in the cached sources. Reproductive behaviour in the wild is unreported.
Breeding
There is no published breeding account for this species. Spawning mode, clutch size, and parental care are unknown, and no aquarium breeding reports are recorded in the available references.
In the aquarium
Parotocinclus longirostris is not established in the aquarium trade, and no husbandry protocol exists in the cached literature. The only firm guidance comes from its natural setting: a tropical, freshwater, demersal fish of the Amazon basin.
By analogy with other small Parotocinclus and the related Otocinclus, it would be expected to require a mature, well-planted tank with abundant biofilm and algae for grazing, gentle current, and clean, warm water — and, given the genus's facultative air-breathing, undisturbed access to the surface. These are inferences from the genus rather than tested recommendations for this species.
Conservation
The IUCN Red List assessed Parotocinclus longirostris as Least Concern in 2018, consistent with a distribution across the wide Amazon basin and no evidence of significant decline. No species-specific threats are itemised in the cached sources; the broad regional pressures on Amazonian freshwaters — deforestation, sedimentation, and hydrological change — apply at the basin scale but have not been linked to a documented decline in this species.