Taxonomy & naming
Neoplecostomus jaguari was formally described by Andrade and Langeani in 2014 in Neotropical Ichthyology, from specimens collected in the ribeirão do Forja and córrego Casca d'Antas, two tributaries of the Rio Jaguari in the Rio Piracicaba-Capivari-Jundiaí sub-basin, upper Rio Paraná basin, Minas Gerais, Brazil. The holotype (LIRP 2277, 3.5 in SL, male) was taken from the ribeirão do Forja at Extrema municipality (22°52′20″S, 46°17′27″W). The Catalog of Fishes (Eschmeyer, CAS) recognises the valid combination Neoplecostomus jaguari under the authority of those two authors.
The genus Neoplecostomus was erected by Eigenmann and Eigenmann in 1888. The family-level placement of the genus has varied across classifications: FishBase currently lists it within Hypoptopomatinae, but the original description and subsequent phylogenetic literature (including Langeani's 1990 genus revision and Roxo et al.'s 2012 molecular work) treat Neoplecostomus as the core member of the subfamily Neoplecostominae, a distinct lineage of small, stream-adapted loricariids of the Brazilian Shield. The site facet follows FishBase; the reader should be aware that much of the primary literature recognises Neoplecostominae as a valid subfamily.
The species epithet jaguari derives from the Tupi-Guaraní compound meaning 'river of the jaguar', in reference to the Rio Jaguari from whose headwater tributaries all known specimens originate.
Morphology
The holotype measures 3.5 in SL; the type series spans 2–3.5 in SL, making N. jaguari a moderately small loricariid — roughly 3.5 in maximum in standard length. The body plan is elongated and dorsoventrally flattened in the manner typical of rheophilic loricariids adapted to life on exposed hard substrates. Meristic data include 9 dorsal soft rays and 6 anal soft rays. A lateronasal plate is present, along with 4–6 posteronasal plates, features noted in the original description.
The most remarkable morphological character of the species is its strong sexual dimorphism in dentition. Females carry 30–38 teeth on the dentary and 30–39 on the premaxillary, while males have only 13–18 dentary teeth and 14–20 premaxillary teeth — approximately a threefold difference in count. Female teeth are described as longer and more slender; male teeth are shorter and more robust. The mandibular width of females (18.5–21.6% of head length) substantially exceeds that of males (11.8–15.7% of head length), reflecting this greater dental load. Males additionally possess dermal flaps and a urogenital papilla that are useful for sex determination in hand.
Habitat
All known material comes from two small tributaries of the Rio Jaguari — the ribeirão do Forja and the córrego Casca d'Antas — in the upper Rio Paraná basin, Minas Gerais. These streams drain high-elevation terrain in the Brazilian Crystalline Shield, a region of ancient Precambrian basement rocks that produce oligotrophic, fast-flowing watercourses with bedrock and boulder substrates.
The original description characterises the habitat as 'high streams in the Brazilian Crystalline Shield'. Specific water-chemistry measurements are not available in the literature consulted. Headwater streams in this region of Minas Gerais are generally cool to seasonally warm (approximately 61–79 °F depending on altitude and season), very soft, oligotrophic, and circumneutral to slightly acidic (approximately pH 6.5–7.5). Dissolved oxygen is high in these well-aerated, stony streams. These are the conditions under which the species' rheophilic morphology — flattened body, sucker mouth — would be most functional.
Feeding
No direct dietary data have been published for Neoplecostomus jaguari. The genus as a whole is understood to be composed of biofilm and periphyton scrapers — algivores and detritivores that rasp microalgae and fine organic matter from rocky substrates in fast-moving water, which is the functional guild occupied by most small rheophilic loricariids of the Brazilian Shield. The striking sexual dimorphism in tooth number and morphology (females with far more, longer, slender teeth; males with fewer, shorter, robust teeth) may reflect different feeding strategies or substrate preferences between the sexes, but this has not been investigated.
Mating
Reproductive behaviour has not been observed or described for Neoplecostomus jaguari in the wild or in captivity. The sexual dimorphism in dentition and mandibular morphology documented by Andrade and Langeani (2014) — along with the presence of dermal flaps and a urogenital papilla in males — confirms that the sexes can be distinguished externally, but nothing is known about courtship, mate choice, or territoriality in this species.
Breeding
No breeding records for Neoplecostomus jaguari exist in captivity or in field studies. The species has not been established in the aquarium trade, and no hobbyist documentation of reproduction has been located. Clutch size, spawning substrate, incubation period, and parental behaviour are all unknown.
In the aquarium
Neoplecostomus jaguari has not been maintained in captivity in any documented account and is absent from the ornamental trade. Its extreme endemism — two small headwater streams in a single Minas Gerais municipality — means collection pressure would pose an obvious conservation concern even if demand existed. Any hypothetical husbandry would need to replicate the oligotrophic, well-oxygenated, fast-moving, cool to moderately warm (61–79 °F) conditions of upper Paraná headwater streams, with clean rocky substrates supporting periphyton growth. No practical guidance can be offered beyond these inferences from habitat data.
Conservation
The IUCN Red List assessed Neoplecostomus jaguari as Data Deficient in December 2020. The Data Deficient listing reflects the species' extraordinary geographic restriction — all known specimens come from just two small tributary streams within a single river sub-basin in Minas Gerais — combined with insufficient survey data to determine population size or trend. A restricted-range species occupying headwater streams in the heavily altered Minas Gerais agricultural landscape would be a credible candidate for threatened status if adequate survey data were gathered.
The upper Rio Paraná basin of Minas Gerais has experienced intensive land-use change from sugar-cane cultivation, eucalyptus forestry, and urban expansion. Headwater streams in this region are vulnerable to sedimentation, irrigation extraction, and loss of riparian buffers. The Rio Piracicaba-Capivari-Jundiaí sub-basin in particular is one of the most densely developed catchments in Brazil. Whether populations of N. jaguari persist in both type-locality streams — or have contracted further — is unknown.