Taxonomy & naming
Hypostomus nematopterus was formally described by Isbrücker and Nijssen in 1984, in the Bulletin of the Zoölogisch Museum Amsterdam (volume 10, number 2, pages 9). The type locality is Alikene Creek, a left-bank tributary of the Camopi River in the Oyapock basin of French Guiana. The Catalog of Fishes (Eschmeyer, CAS) recognises the valid combination Hypostomus nematopterus.
This species is catalogued by aquarium enthusiasts under the code L060, one of the DATZ registration numbers assigned to loricariids before formal descriptions were widely circulated in the hobby. It circulates in English-speaking aquarium circles as the Thread-finned Pleco — a reference to the elongated filaments the fish produces on the dorsal and caudal fins, a feature that distinguishes it visually from many congeners. The authority abbreviation paired with the common name L060 appears consistently in trade literature and hobbyist databases such as PlanetCatfish.
Within Loricariidae the species is placed in subfamily Hypostominae, and within Hypostomus it belongs to the broader morphological cluster of spotted-pattern species whose ground colour is dark and overlaid with pale dots or blotches.
Morphology
Adults reach a recorded maximum of 4 in standard length (SL), based on the reference specimen catalogued on FishBase (Ref. 36817). Total length in living fish is somewhat greater, though no precise TL measurement appears in the primary sources consulted.
The body plan follows the typical Hypostomus armour: overlapping bony scutes cover the flanks and dorsum, and the broad, flat head supports a ventrally placed sucking disc. The colour pattern consists of pale spots on a dark brown to almost black background — a common scheme within the genus, shared with dozens of other Hypostomus species but combined here with the distinctive fin filaments that give the fish its vernacular name. The posterior rays of the dorsal fin and the lobes of the caudal fin extend into thread-like filaments in fully mature individuals.
As in the broader genus, H. nematopterus is capable of facultative air-breathing — a physiological trait shared across Hypostomus that allows the fish to gulp atmospheric oxygen when dissolved oxygen in the water is low, such as during the dry season when water levels drop and organic matter accumulates in pools.
Habitat
Hypostomus nematopterus is known exclusively from the Oyapock River basin, which straddles the border between French Guiana and the Brazilian state of Amapá. The type locality, Alikene Creek, is a tributary to the Camopi River within this drainage.
Field data cited in the primary literature (FishBase Ref. 90186) describe a rheophilic microhabitat: rocky substrates of boulders, stones, gravels, and sand in fast-moving water, from headwaters to areas upstream of the lower falls. Exposed wet rocks in this zone are often colonised by aquatic flowering plants of the family Podostemaceae — specifically Mourera fluviatilis and Apinagia richardiana — species associated with fast-running, oxygen-rich Guiana Shield rivers. These rock faces and crevices, perpetually swept by current and encrusted with biofilm, represent the core foraging and refuge habitat of the species.
The Oyapock basin drains Guiana Shield geology, producing soft, acidic to near-neutral blackwaters and clearwaters typical of ancient crystalline rock regions. Specific field measurements of pH and temperature at the type locality are not available in the sources consulted.
Feeding
As a member of Hypostomus, H. nematopterus is an algae scraper and biofilm grazer. The ventral sucking disc and stout, multi-cusped teeth are adapted for rasping diatoms, filamentous algae, and associated microbial films from hard substrates — boulder faces, exposed bedrock, submerged stones, and the stems of Podostemaceae.
In the aquarium, the same feeding apparatus translates naturally to sinking algae wafers, spirulina tablets, blanched vegetables such as courgette (zucchini) and cucumber, and the biofilm that develops on any smooth hardscape over time. Meaty foods are not a dietary requirement and should not form the bulk of captive rations. Driftwood provides supplementary surface area for biofilm growth and also appears to be grazed incidentally, as is common in Hypostomus kept in furnished tanks.
Mating
No field or aquarium observations of courtship behaviour in H. nematopterus are recorded in the sources consulted. General loricariid biology suggests males establish territories around suitable shelter sites — crevices between boulders or undercut rock faces — and defend them against rival males during the reproductive period. Given the rheophilic habitat of this species, courtship likely takes place among boulders in fast-flowing reaches, consistent with the breeding biology of other rheophilic Hypostomus.
No aquarium breeding reports for this species appear in the hobbyist literature available, which is unsurprising given its rarity in trade: specimens are occasionally exported from French Guiana as wild-caught individuals, and captive-bred stock is essentially unavailable.
Breeding
No confirmed breeding reports for Hypostomus nematopterus in captivity appear in the sources consulted. In the broader genus, cave or crevice spawning with paternal brood care is the norm: the male selects a cavity among rocks or submerged wood, the female deposits adhesive eggs on the cavity walls, and the male guards and fans the clutch until the fry are free-swimming. Whether H. nematopterus follows this pattern precisely is unconfirmed.
The restricted natural range of this species and its near-absence from captive collections means breeding data are unlikely to accumulate rapidly. Any future captive success would represent a meaningful conservation contribution, given the species' Endangered status.
In the aquarium
Hypostomus nematopterus is rarely encountered in the aquarium trade. Wild-caught specimens are occasionally exported from French Guiana; captive-bred stock is not known to exist. Any fish obtained will almost certainly be wild-caught, which raises both cost and acclimation considerations.
The rheophilic nature of the species demands strong water movement and high dissolved oxygen. A powerful canister filter combined with a supplementary powerhead or spray bar is advisable. Décor should replicate the boulder-strewn, fast-water environment of Guiana Shield streams: large smooth stones and rounded river pebbles, minimal fine sediment, and robust plants or none at all. The fish requires hiding places among and beneath rocks.
Water chemistry consistent with the soft, clear Guiana Shield environment is recommended: mildly acidic to neutral pH (6.5–7.2), low to moderate hardness, and temperatures in the range of 75–82 °F. The fish should not be kept in warm, sluggish, heavily planted community tanks — these conditions are poorly matched to its wild ecology.
Given the species' Endangered status and rarity in the hobby, acquisition should be considered carefully. Providing appropriate rheophilic conditions and attempting captive breeding would represent a tangible contribution to ex-situ knowledge of this threatened taxon.
Conservation
The IUCN Red List assessed Hypostomus nematopterus as Endangered (EN) on 14 January 2021, under criterion B1ab(iii). The listing reflects a restricted extent of occurrence (EOO) confined to the Oyapock River basin, combined with evidence of continuing decline in habitat quality.
The Oyapock drainage is a single river system. This geographic confinement means that any significant deterioration of water quality, riparian forest cover, or hydrology across the basin threatens the entire known range of the species simultaneously. There is no satellite population in an adjacent drainage that could act as a source for recolonisation. Threats identified in the IUCN assessment include habitat degradation — likely reflecting gold mining (garimpo) pressure common across French Guiana and Amapá, deforestation, and the associated sedimentation that buries the rocky substrates on which H. nematopterus depends.
The species holds no CITES listing and has no established captive population. Its scarcity in the aquarium trade means ornamental collection pressure is not a documented threat, but it also means there is no established ex-situ insurance population. Conservation of H. nematopterus is, in practical terms, entirely dependent on the protection of intact Oyapock basin habitat — an argument for sustained oversight of this biodiverse Guiana Shield corridor.