Taxonomy & naming
Poropuntius melanogrammus was described by Tyson R. Roberts in 1998 in his monographic review of the tropical Asian cyprinid genus Poropuntius, published in the Natural History Bulletin of the Siam Society. The holotype (CAS 94269, 2 in SL) was collected from a mountain stream in the Meklong tributaries of western Thailand. Roberts' 1998 revision was the primary authority establishing the species' morphological diagnosis and its distinctions from congeners across the region.
The genus Poropuntius belongs to the family Cyprinidae and encompasses medium-sized barbel-like fishes distributed across mainland Southeast Asia and adjacent drainages. The genus is not to be confused with the broad, now-dismembered genus Puntius, from which many Asian barbs were redistributed following the systematic revisions of the 2000s and 2010s; Poropuntius was already recognised as a distinct lineage prior to those splits. A subsequent study of regional Poropuntius fauna covering the Chao Phraya, Mae Klong and Salween drainages (published in MDPI Fishes) recovered a specimen (UF 237509, 3.5 in SL) from Ulong Creek, Khwae Noi drainage, Kanchanaburi Province in 2015, confirming the species' continued presence in the Mae Klong system.
The Catalog of Fishes (Eschmeyer, CAS) is the authority for the current valid name, Poropuntius melanogrammus Roberts, 1998.
Morphology
Poropuntius melanogrammus is a slender, moderately elongate cyprinid. The original holotype measured 2 in SL, and FishBase records a maximum length of 2 in SL for male or unsexed individuals; however, a 2015 specimen from the Khwae Noi drainage reached 3.5 in SL, suggesting the species may attain larger sizes than the holotype series indicated.
The species is characterised by the dark lateral stripe that gives it its name — melanogrammus derives from Greek melanos (dark/black) and gramme (line). A notable anatomical feature reported in Roberts' original description is the absence of visible barbels and the presence of a cornified sheath on the lower jaw, a hard keratinised structure associated with scraping algae or biofilm from rocky substrates. This trophic morphology is a diagnostic trait that helps distinguish P. melanogrammus from other members of the genus. The species is described as benthopelagic in habit, consistent with a bottom-associated lifestyle in stream environments.
Habitat
Poropuntius melanogrammus is known exclusively from the Mae Klong river system in western Thailand, specifically from swift, clear-water mountain tributaries in the Khwae Noi (Kwai Noi) drainage, Kanchanaburi Province. Roberts' original description placed the holotype collection in a mountain stream among Meklong tributaries, and the 2015 MDPI Fishes specimen was taken from Ulong Creek in the same drainage.
The habitat profile — swift, clear-water streams in highland terrain — is consistent with a rheophilic species adapted to well-oxygenated, current-swept substrates. Such environments in western Thailand are characterised by clean gravel, rock and cobble bottoms, where biofilm and periphyton growth provide a food source for hard-jaw scrapers. Water temperatures in these upland western Thai streams are warm tropical but moderated by elevation and flow, and the water is typically soft to moderately hard with a near-neutral pH reflecting the mixed geology of the Tenasserim Hills drainage divide.
Feeding
The cornified sheath on the lower jaw of Poropuntius melanogrammus is a strong morphological indicator of a scraping feeding mode, in which the fish rasps algae, diatoms and biofilm from hard substrates such as rocks and cobble. This kind of trophic specialisation is found in various rheophilic cyprinids adapted to fast-flowing, clear streams where periphyton is the dominant primary production pathway.
Beyond what can be inferred from jaw morphology and habitat, direct dietary data for this species are sparse in the available literature. In an aquarium setting, species with analogous jaw adaptations typically accept sinking algae wafers, spirulina-enriched foods and blanched vegetable matter in addition to small invertebrate foods. As with most barbs, an omnivorous diet with a strong plant-matter component is likely appropriate.
Mating
No specific observations of courtship or mating behaviour have been reported for Poropuntius melanogrammus in the literature. As a member of family Cyprinidae, it can be expected to follow the egg-scattering, non-guarding reproductive pattern typical of barbs: a gravid female is pursued by one or more males, and eggs and milt are released together over substrate or among vegetation without the formation of a pair bond or territory beyond the brief act of spawning.
In rheophilic barbs from swift streams, spawning often takes place over coarse gravel or cobble, where water movement helps aerate eggs and disperses them into interstitial spaces away from adult predation. No breeding has been documented in captivity for this species.
Breeding
Poropuntius melanogrammus has not been bred in captivity in any documented account. Based on the biology of comparable rheophilic Poropuntius and related cyprinids, the species would be expected to be an egg-scatterer with no parental care: eggs are broadcast over the substrate and left to develop independently, with adults providing no guarding, nest construction or brooding of any kind. Adults likely consume eggs opportunistically after spawning.
For any attempt at aquarium breeding, providing well-oxygenated, moderately flowing water over a coarse gravel substrate would be the most habitat-appropriate approach, mirroring the swift mountain-stream conditions of the Khwae Noi drainage. Fry, if obtained, would presumably require fine live foods such as infusoria and newly hatched brine shrimp nauplii in the early stages.
In the aquarium
Poropuntius melanogrammus is essentially unknown in the aquarium hobby. Its restricted natural range, specialised habitat requirements and lack of hobbyist documentation mean it is not available through the ornamental trade and has not been maintained or bred in captivity in any reported account. The species' requirement for swift, well-oxygenated, clear water and its apparent trophic dependence on hard-substrate biofilm would make it a demanding subject even if available.
For the specialist keeper of rheophilic Southeast Asian cyprinids, a suitable setup would prioritise strong filtration, high water turnover to maintain oxygen levels, smooth rock and cobble decor to encourage natural feeding behaviour, and soft to moderately hard water with a near-neutral pH reflecting the Mae Klong upland environment. Water temperature in the low-to-mid twenties Celsius would approximate highland stream conditions. The species is best regarded as a scientific and conservation curiosity rather than a practical aquarium subject at present.
Conservation
Poropuntius melanogrammus is assessed as Data Deficient (DD) on the IUCN Red List, a status recorded on FishBase as reflecting a 2011 assessment. Data Deficient indicates that insufficient information exists to assign a threat category — not that the species is necessarily secure. Given its apparently very restricted range within a single drainage system in western Thailand, any narrowing of available habitat could have disproportionate consequences for the population.
The Khwae Noi (Kwai Noi) river and its tributaries in Kanchanaburi Province have been affected by hydroelectric development, most notably the Khao Laem reservoir and associated infrastructure. Upstream tributary habitats in the Tenasserim range are relatively intact due to the area's proximity to protected forest zones and the Thailand-Myanmar border region, but agricultural encroachment, water extraction and sedimentation from deforestation remain potential pressures on swift, clear-water stream species throughout western Thailand. A targeted survey to establish population size, range extent and habitat condition would be the prerequisite for a meaningful threat assessment.