Taxonomy & naming
Parotocinclus fluminense was described by Roxo, Melo, Silva and Oliveira in 2017 in the journal Zootaxa (volume 4232, number 2, pages 260–270), in a paper on new species of Parotocinclus from the coastal drainages of Rio de Janeiro, southeastern Brazil. The Catalog of Fishes (Eschmeyer, CAS) lists it under spid 74761 with the authority Roxo, Melo, Silva & Oliveira, 2017.
It is a member of the subfamily Hypoptopomatinae within the family Loricariidae — the lineage of small, dwarf armoured suckermouth catfishes. The specific epithet derives from the Baixada Fluminense, the lowland region surrounding the city of Rio de Janeiro where the species occurs.
Morphology
Parotocinclus fluminense is one of the smaller members of its genus, reaching about 1 in in standard length. It shows the typical hypoptopomatine body plan: a small, depressed, fully armoured body covered in bony lateral scutes, with a ventral suckermouth adapted for clinging and grazing.
Beyond maximum size, granular morphological and colour data for this species are not summarised in the sources available here, and so are not asserted.
Habitat
The species is endemic to the coastal drainages of Rio de Janeiro state (the Baixada Fluminense region) in southeastern Brazil. It is a freshwater, demersal fish of tropical waters.
Its recorded habitat is in association with marginal submerged vegetation covering the bottom and the borders of headwaters, in moderate-flowing sections of rivers. No specific water-chemistry or temperature figures for this species are published in the sources available here.
Feeding
Parotocinclus fluminense has a model-estimated trophic level of about 2.4, consistent with the herbivore/detritivore feeding typical of the genus — that is, grazing on algae, biofilm, and fine organic detritus from submerged surfaces. No direct gut-content or feeding study specific to this species is cited in the sources available here, so the figure should be read as an estimate rather than a measured diet.
Mating
No data on courtship or mating behaviour for Parotocinclus fluminense are published in the sources available here.
Breeding
No data on reproduction, spawning mode, clutch size, or parental care for Parotocinclus fluminense are published in the sources available here. FishBase notes the species has high resilience, implying a relatively short population-doubling time, but no direct breeding observations are cited.
In the aquarium
Parotocinclus fluminense is not an established aquarium-trade species, and no husbandry data for it are published in the sources available here. Its small size and association with vegetated, moderate-flowing headwater margins are consistent with the general profile of dwarf Hypoptopomatinae, but specific care recommendations cannot be drawn from the available material without speculation.
Conservation
The IUCN Red List assessed Parotocinclus fluminense as Near Threatened (NT) on 15 December 2020, under criteria B1b(iii)+2b(iii) — a listing driven by its small geographic range and a continuing decline in the quality of its habitat. The coastal drainages of the Baixada Fluminense around Rio de Janeiro are among the most urbanised and degraded in Brazil, with pollution, water abstraction, and loss of marginal vegetation posing ongoing pressures on the small headwater habitats this species depends on.