Taxonomy & naming
Poropuntius tongnunui was described in 2026 by Lawrence M. Page, Zachary S. Randall, Wansuk Tangjitjaroen, Hạnh Minh Phạm and Hoàng Đức Đạt, as part of a broader revision of Poropuntius across the Chao Phraya, Mae Klong, Salween and Tenasserim river basins of Southeast Asia. It belongs to the genus Poropuntius, part of the subfamily Cyprininae within the family Cyprinidae, diagnosed across the genus by large serrations on the posterior edge of a robust dorsal-fin spine, a strongly forked caudal fin, tubercles covering the snout and extending over the lacrimal bones, 8½ branched dorsal-fin rays, 5½ branched anal-fin rays and 9 pelvic-fin rays.
The describing authors found P. tongnunui to be most closely related, based on molecular data, to an as-yet-undescribed population from the Pai River drainage — referred to only as the 'Pai River species' because just a single specimen was available — and, more distantly, to P. opisthopterus of the Salween basin. It differs from the Pai River species in lateral-line scale count (28-33 vs. 24) and from P. opisthopterus in the position of the dorsal-fin origin, the presence of black submarginal stripes on the caudal fin, and larger scales generally. It is also morphologically similar to the wide-ranging P. laoensis but consistently carries shorter barbels regardless of body size, and the two are genetically distant. The specific epithet honours Dr. Sampan Tongnunui of the Department of Conservation Biology, Mahidol University's Kanchanaburi Campus, for his contributions to the knowledge of Thailand's fishes.
Morphology
Poropuntius tongnunui is an elongated cyprinid; the holotype measures 5.9 in in standard length, and the largest known specimen reaches 6.9 in SL. Body depth at the dorsal-fin origin runs 24.9-33.1% of standard length, narrowing sharply to 16.4-20.2% at the caudal peduncle. The snout is pointed and covered with tubercles that usually extend almost to the eye, with some individuals also carrying smaller tubercles across the top of the head; the mouth is horseshoe-shaped, with fleshy lips that thin toward the middle, plicae (fine ridges) on the front half of the upper lip, and a lower lip that is continuous or only slightly interrupted at the midline, without the cornified (hardened) edge some related species carry.
Two pairs of barbels are present — a maxillary barbel reaching to about the middle of the eye and a mandibular barbel extending past the eye, sometimes as far as the rear edge of the preopercle (gill-cover bone). The dorsal-fin origin sits over or just behind the pelvic-fin origin, and the largest dorsal-fin spine is robust, carrying 18 to 24 large serrations on its rear margin and running longer than half the body depth, occasionally nearly matching it. Meristic counts include 28 to 33 (usually 28-30) lateral-line scales, 10 to 14 predorsal scales, 14 scales around the caudal peduncle, 8½ branched dorsal-fin rays, 5½ branched anal-fin rays, 16-17 branched caudal-fin rays, 14-17 pectoral-fin rays, 9 pelvic-fin rays, and 41 total vertebrae. Body shape and dorsal-spine length vary somewhat with the stream environment: an individual from the swift mountain streams of the upper Khwae Yai drainage was notably more slender and longer-spined than the holotype, collected further downstream.
Live colouration is silver over the head and body, pale yellow dorsally in some individuals, with melanophores (dark pigment cells) concentrated on the caudal peduncle at the base of the tail fin. The fins are mostly clear or faintly orange, sometimes more strongly orange on the paired fins, and the caudal fin carries black submarginal stripes along both lobes, with the lower stripe darker than the upper. In preservative, the body turns dark brown above and lighter brown below, with the caudal-peduncle pigmentation forming a large black spot and the caudal-fin stripes persisting.
Habitat
Poropuntius tongnunui inhabits creeks and small-to-large rivers over rocky substrate in the upper Khwae Noi and upper Khwae Yai drainages of the Mae Klong River basin, spanning Kanchanaburi, Tak and Uthai Thani provinces in western Thailand. Much of its known range falls within the Western Forest Complex, one of the largest and most highly protected areas of contiguous forest in Southeast Asia, and the species is described as common in the clear, fast-flowing streams of the Huay Kha Khaeng, Thung Yai Naresuan and Umphang wildlife sanctuaries, including at the type locality itself.
Populations in the upper Khwae Noi drainage may have been negatively affected by construction of the Vajiralongkorn Reservoir and by development around nearby municipalities, but the sanctuary populations drain large tracts of forested land and appear to suffer only minor human impact. Young-of-the-year as small as 0.7 in SL have been collected from the upper Khwae Yai in Umphang District, indicating the species breeds within these same sanctuary drainages rather than migrating elsewhere to spawn.
Feeding
No dietary study specific to Poropuntius tongnunui has been published. The tubercle-covered snout typical of the genus, together with the fleshy, plicate lips, is broadly consistent with a benthic feeding style — grazing algae and biofilm from rock surfaces while also taking small invertebrates — but this has not been directly documented for P. tongnunui, and its feeding ecology remains effectively unstudied.
Mating
Sexes of Poropuntius tongnunui could not be reliably distinguished by external characters in the specimens examined for its description, and no courtship behaviour has been documented. The tubercles covering the snout are present on individuals across a range of sizes, but too few collecting dates were available to determine whether their development varies seasonally, as breeding tubercles often do in other cyprinids.
Breeding
No spawning has been documented in the wild or in captivity for Poropuntius tongnunui. The presence of young-of-the-year as small as 0.7 in SL within the same protected sanctuary streams where adults occur indicates the species completes its life cycle locally rather than undertaking a long-distance spawning migration, but details of courtship, egg deposition or parental care, if any, have not been published.
In the aquarium
Poropuntius tongnunui is not established in the aquarium trade. Like most of its genus, it is a poorly known river barb rather than an ornamental species, and no husbandry data exist. Its documented preference for clear, fast-flowing, rocky-bottomed streams suggests that, were it ever kept, it would need strong water movement, high oxygenation and a spacious, long aquarium rather than the still, planted setups suited to many popular barbs; its adult size of up to 6.9 in SL also rules it out as a nano or small-community fish.
Conservation
Poropuntius tongnunui has not been evaluated by the IUCN Red List, having been described only in 2026. Much of its known range lies within the Western Forest Complex — the Huay Kha Khaeng, Thung Yai Naresuan and Umphang wildlife sanctuaries — one of the least disturbed and most highly protected areas in Southeast Asia, where the species is described as common in clear, fast-flowing streams draining largely forested land. The main documented concern is in the upper Khwae Noi drainage, where populations may have been negatively affected by construction of the Vajiralongkorn Reservoir and by development around nearby municipalities; no other specific threats have been reported.