Taxonomy & naming
Hypostomus nigrolineatus was described by Zawadzki, Carvalho, Birindelli and Azevedo in 2016 in Ichthyological Exploration of Freshwaters (volume 27, number 3, page 273). The Catalog of Fishes (Eschmeyer, CAS) recognises the name as valid. The species is unrelated to the common aquarium fish Panaque nigrolineatus (Peters, 1877), which carries an identical species epithet but belongs to a different genus and a different evolutionary lineage entirely; the shared epithet reflects only the same Latin phrase applied independently by different authors to fishes that happen to display dark linear markings.
The type locality is in the Rio Jequitinhonha basin, Minas Gerais state, eastern Brazil. Paratypes were also taken from the Rio Pardo basin, a separate eastern coastal drainage also originating in Minas Gerais. Both rivers drain eastward to the Atlantic, making this a species of the eastern Brazilian coastal drainage systems rather than the Amazon or Paraná basins.
Hypostomus nigrolineatus is placed in subfamily Hypostominae (Armbruster, 2004), within the broadly construed genus Hypostomus Lacépède, 1803. The description provides a morphological diagnosis distinguishing it from congeners by its colour pattern and several osteological and meristic characters.
Morphology
The original description provides the most complete morphological account available. Paratypes range in size from 4–8.5 in standard length (SL), with some individuals exceeding 7.5 in SL — indicating that this is a moderately large Hypostomus for its drainage.
The colour pattern is the most striking diagnostic feature and the basis for the species name. The head and anterior portion of the trunk bear dark spots. The posterior flanks carry dark longitudinal stripes — a character described in the original diagnosis as unique in Hypostomus, setting H. nigrolineatus apart from the numerous congeners that typically display spotted, blotched, or uniform patterning but not clear lateral striping. This combination of anterior spots and posterior stripes is the primary visual character.
Meristic data from the original description include 9–37 teeth on the premaxilla and 10–39 on the dentary — a wide range suggesting ontogenetic variation or population-level variation in tooth number, as occurs in other Hypostomus. The dentary is angled at approximately 90°. The median plate series contains 25–29 plates, and a moderate median keel of odontodes is present on most body plates. Scutelet coverage on the abdomen is incomplete in young specimens. These characters collectively support the species' placement within Hypostomus while distinguishing it from its nearest neighbours.
Habitat
The type locality is in the Rio Jequitinhonha basin, Minas Gerais, and paratypes extend the known range to the Rio Pardo basin — the only two river systems from which the species has been documented. Both are eastern Brazilian coastal drainages originating in the montane uplands of Minas Gerais and flowing east-northeast to the Atlantic.
These rivers drain the Atlantic Forest biome (or its degraded remnants) through highly weathered Precambrian terrain. They are typically clearwater to slightly tannic rivers with low to moderate conductivity and slightly acidic to neutral pH. The upper reaches where loricariids are typically concentrated involve rocky substrates and moderate to swift current; the lower reaches become broader, slower, and more turbid.
Specific water chemistry data from the collection localities of H. nigrolineatus are not available in the literature consulted. The eastern Atlantic coastal rivers of Minas Gerais are subject to significant anthropogenic alteration, including impoundments and agricultural runoff, which has modified much of the original habitat.
Feeding
No feeding data specific to H. nigrolineatus have been published. Based on the dentition described — numerous small teeth on both premaxilla (9–37) and dentary (10–39) with a dentary angle of approximately 90° — H. nigrolineatus does not appear to belong to the spoon-toothed, wood-eating cochliodon group. This suggests feeding biology more typical of the broader Hypostomus grade: grazing on aufwuchs (algae, diatoms, cyanobacteria) and biofilm scraped from rock, wood, and other hard substrates, with fine detritus consumed incidentally.
In aquaria, such species are typically maintained on algae wafers, spirulina products, and blanched vegetables. No captive specimens have been reported, so these general Hypostomus husbandry norms are the only available guide.
Mating
Mating behaviour in H. nigrolineatus has not been described. As for other members of the genus, breeding males are expected to develop secondary sexual characters — including more pronounced interopercular odontodes — and to exhibit territorial behaviour around preferred cavity sites. No observations from field or aquarium are available for this species.
Breeding
Breeding in H. nigrolineatus has not been documented. The genus Hypostomus is generally characterised by cave or cavity spawning with paternal care, in which the male guards and fans the egg clutch until fry disperse. No species-specific breeding records exist.
In the aquarium
Hypostomus nigrolineatus is not established in the aquarium hobby, and no captive husbandry records have been published. Occasional wild-caught specimens from eastern Brazilian rivers are noted as sometimes appearing in the specialist trade (ETYFish Project), but the species is not a mainstream aquarium fish.
Note that the epithet nigrolineatus is also carried by the much better-known and commercially available Panaque nigrolineatus (the royal pleco, L190 / L191 / L330). Hobbyists purchasing fish labelled 'nigrolineatus' in a general context are almost certainly receiving Panaque nigrolineatus, not this Hypostomus. The two species differ in genus, subfamily tribe, distribution, maximum size, and dietary specialisation, and should not be confused.
If Hypostomus nigrolineatus were to be kept, water parameters consistent with Minas Gerais Atlantic Forest rivers — moderate temperature (around 72–82 °F), slightly acidic to neutral pH, low to moderate hardness — would serve as a starting framework, with the caveat that no husbandry data have been recorded for the species.
Conservation
Hypostomus nigrolineatus has not been assessed by the IUCN Red List. The species was described in 2016 from the Rio Jequitinhonha and Rio Pardo basins — two eastern Brazilian river systems that have experienced extensive habitat alteration through dam construction, agricultural runoff, eucalyptus plantation expansion, and deforestation of the remaining Atlantic Forest remnants in Minas Gerais.
The Rio Jequitinhonha in particular is heavily modified along much of its length, and the Minas Gerais Atlantic Forest is one of the most fragmented and threatened biomes in South America. Whether populations of H. nigrolineatus are sufficiently robust and distributed to withstand ongoing habitat degradation cannot be determined from the available data, but the ecological context is one of elevated concern. A formal IUCN assessment would require updated distributional data and population survey work.