Taxonomy & naming
Neoplecostomus microps was originally described by Franz Steindachner in 1877 as Plecostomus microps, published in the Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften, Mathematisch-Naturwissenschaftliche Classe (volume 74(1. Abth.), pages 688[130], plate 13). The type locality is given as 'Rio de Janeiro (possibly Rio Parahyba)' — an early collection where geographic attribution was imprecise; lectotype NMW 45337.1, with one paralectotype, lectotype selected by Langeani (1990). The Catalog of Fishes (Eschmeyer, CAS) lists the valid combination as Neoplecostomus microps (Steindachner 1877), with parenthetical authority indicating transfer from the original Plecostomus.
The genus Neoplecostomus was erected by Eigenmann & Eigenmann (1888) for a group of small loricariids from coastal Atlantic Forest drainages of south-eastern Brazil. It currently contains approximately 20 described species. Subfamilial placement has been debated: Armbruster's (2004) morphological analysis placed Neoplecostomus in a broadly defined Hypostominae, while later molecular work recognised a distinct Neoplecostominae (Chiachio et al. 2008; Pereira et al. 2010). The Catalog of Fishes currently treats the genus within Hypoptopomatinae. Molecular phylogenies (Roxo et al. 2012, 2014, 2017; Silva et al. 2019) consistently recover Neoplecostominae as a clade embedded within or closely allied to the broader Hypoptopomatinae sensu lato, a situation the literature acknowledges as not fully resolved at the subfamilial level.
The code LDA034 was assigned by Das Aquarium magazine; no L-number has been assigned.
Morphology
Adults reach approximately 4 in standard length (SL), placing this species toward the smaller end of the Neoplecostomus size range. Body shape is typical of the genus and of small rheophilic loricariids generally: depressed, robust, and covered in overlapping bony scutes, with a broad, flat head and a ventral suctorial mouth. Coloration is cryptic — typically mottled grey-brown to olive-brown above, matching the rock and gravel substrates of its native streams, with a paler underside.
PlanetCatfish image series for this species shows a compact, moderately patterned fish. The eyes are notably small relative to head size — consistent with the species epithet microps (small-eyed) — a feature that Steindachner used as a primary character in the original description.
Sexual dimorphism in Neoplecostomus microps is documented from hobbyist observations: males develop an epidermal outgrowth or fleshy pad on the inner surface of the pelvic fin, visible in PlanetCatfish images labelled 'male'. Additionally, males and females differ in urogenital anatomy: males possess separate anal and urogenital pores, whereas females have a single combined pore. Gravid females are noticeably broader-bodied when viewed from above.
Habitat
Neoplecostomus microps is endemic to south-eastern Brazil, with its distribution centred on the Paraíba do Sul River basin of Rio de Janeiro state; PlanetCatfish also records occurrences from the Macaé drainage of coastal Rio de Janeiro. These are Atlantic Forest stream systems characterised by clear, cool water, rocky or gravel substrates, and moderate to strong current.
Field data cited by PlanetCatfish from Brito et al. (2016, Biota Neotropica 16(2)) provide the most detailed environmental measurements available: at collection sites, water temperature ranged from 53–78 °F (consistent with cool montane streams at higher elevation and warmer lowland stretches), electrical conductivity from 12.2 to 73.2 µS/cm (very soft, low-mineral water), and dissolved oxygen from 7.45 to 10.78 mg/L (well-saturated). FishBase notes a temperature preference of 68–77 °F for husbandry purposes, though this underrepresents the cold end of the natural range.
The cold tolerance of N. microps — with documented field temperatures below 54 °F — is remarkable among loricariids and reflects the montane character of portions of its range. Streams of the Serra dos Órgãos and adjacent ranges in Rio de Janeiro state receive cool temperatures in winter months from both altitude and latitude.
Feeding
Neoplecostomus microps, like other members of the genus, is an aufwuchs grazer and periphyton scraper. Its ventral mouth, fine teeth, and association with rocky substrates are consistent with a diet centred on biofilm, diatoms, filamentous algae, and fine organic detritus scraped or rasped from rock surfaces. The genus is not xylophagous (wood-eating), in contrast to Panaque or Panaqolus.
No detailed gut-content studies appear to have been published specifically for N. microps, but the feeding ecology of several Neoplecostomus species has been broadly described in the context of Atlantic Forest stream ichthyology. These streams typically support rich periphytic algal communities on rocks in riffles, which form the dietary base for many rheophilic suckermouth catfishes.
In captivity, the few hobbyists who have maintained N. microps report acceptance of algae wafers, spirulina discs, blanched vegetables (courgette, spinach, cucumber), and sinking pellets. The fish grazes actively on biofilm established on rock surfaces and any driftwood offered. Supplementation with occasional small invertebrate foods (frozen chironomid larvae, Artemia) may support conditioning for breeding.
Mating
Mating behaviour in Neoplecostomus microps has not been described in published literature. PlanetCatfish carries no breeding report for this species as of the time of writing.
Hobbyist image documentation on PlanetCatfish does, however, provide useful sexual dimorphism information useful for pairing: males bear an epidermal growth on the pelvic fin and possess separate anal and urogenital pores (versus the single combined pore of females), allowing sexing of conditioned adults without invasive examination. These are stable characters in adults.
Conditioned females are noticeably wider-bodied than males when viewed from above — a typical loricariid gravid condition. The combination of cool, well-oxygenated water and varied nutrition (biofilm, vegetables, and occasional protein) is most likely to bring N. microps into reproductive condition, based on the general husbandry principles for rheophilic Atlantic Forest loricariids.
Breeding
No successful captive breeding of Neoplecostomus microps has been documented in the published literature or on PlanetCatfish. This reflects the species' overall rarity in the hobby and its demanding husbandry requirements rather than necessarily an inherent difficulty in breeding.
The reproductive mode of the genus is not well documented, but by analogy with other small rheophilic loricariids from similar Atlantic Forest habitats (such as Rineloricaria and Hypostomus species from the same drainages), sheltered crevice- or cave-spawning with some degree of paternal care would be the expected mode. Eggs deposited under flat stones in areas of moderate current, fanned by the male, would be consistent with the ecological setting.
A spawning trigger for this species would logically involve simulating the seasonal cycle of its montane habitat: a cooler, lower water period (simulating the drier, cooler austral winter in south-eastern Brazil, approximately June–September, with temperatures potentially dipping to 57–64 °F) followed by warming water and increased food availability replicating the austral spring onset.
In the aquarium
Neoplecostomus microps is extremely rarely available to hobbyists outside Brazil. It has no commercial trade name beyond its LDA034 code and the informal name 'Small-eyed Neoplecostomus', and no import pipeline exists. Specimens occasionally reach European hobbyists via specialist importers and Brazilian exports, but availability is sporadic and unpredictable.
The species' cold tolerance — documented field temperatures reaching 52–54 °F — makes it of particular interest to temperate-country keepers, as it can theoretically be kept in unheated aquaria in cool rooms or even coldwater setups. However, it is not a coldwater fish in the strict sense: it also tolerates warmer water up to approximately 77 °F, and its optimal husbandry range is probably 61–72 °F.
A tank for N. microps should replicate its native habitat as closely as practical: abundant smooth rocks and cobbles creating caves and crevices, strong water flow and high oxygenation (a spray bar or powerhead directed against the glass surface is helpful), and a substrate of fine gravel or sand. Water should be soft and low in mineral content, reflecting the very low conductivity (as low as 12 µS/cm) recorded in the wild. Weekly partial water changes of 25–30% maintain quality. The fish is peaceful toward other species but will defend territories against conspecifics; a group of one male to two or three females in a 100-litre tank with ample rockwork is appropriate.
This species will not thrive in a warm tropical community tank without deliberate cooling. It is best housed with other cool-water species or alone as a biotope specimen.
Conservation
Neoplecostomus microps is assessed as Least Concern (LC) on the IUCN Red List, with the assessment dated 15 January 2021. The assessment reflects a distribution across multiple river systems in Rio de Janeiro state, an absence of evidence of significant population decline, and the species' apparent tolerance of a range of stream conditions within its native habitat.
However, the broader context gives reason for caution. The Atlantic Forest biome — of which south-eastern Brazilian coastal river systems are an integral part — is one of the most heavily deforested and degraded biomes on Earth, retaining only roughly 12–15% of its original extent. Stream systems in the Paraíba do Sul basin have been heavily affected by urbanisation, agriculture, and hydropower development. The genus Neoplecostomus as a whole is highly endemic, with each species typically restricted to one or a few river basins; habitat degradation therefore poses a real long-term risk even for species currently assessed as Least Concern.
N. microps shares its Paraíba do Sul range with the Critically Endangered Delturus parahybae, illustrating the conservation sensitivity of this basin's rheophilic loricariid fauna. Ongoing monitoring is warranted.