Taxonomy & naming
Tachysurus platystomus was described in 2026 by Weihan Shao and E Zhang, with co-authors Xingwei Cai and Tan Duc Nguyen, in a paper published in the journal Animals that combined mitochondrial DNA and detailed morphometrics to resolve the wide-ranging nominal species Tachysurus virgatus (Oshima, 1926) into ten separately evolving lineages across coastal south China and central-northern Vietnam. Populations long treated as a single species turned out to be reciprocally monophyletic and geographically isolated, each restricted to its own coastal drainage.
T. platystomus belongs to Bagridae, genus Tachysurus, within the T. virgatus species group. Morphologically it forms its own distinct morph-group (Morph-Group C) with its sister species T. heterofasciatus — the two share a moderately (rather than deeply) forked caudal fin and an unusually high vertebral count of 35–36, versus 30–34 elsewhere in the group. The pair shows 2.1% mitochondrial (cytochrome b) divergence and, per the authors, clear accompanying differences in body proportions and coloration.
The holotype (HAIF01, 3.5 in standard length) was collected by Weihan Shao in July 2020 from the Huangjiang River (rendered "Huang River" in the Catalog of Fishes) at Haifeng County, Guangdong Province — a coastal river draining into the South China Sea. Paratypes came from the same locality. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) lists Tachysurus platystomus Shao & Zhang, 2026 as the valid name, with no synonyms.
Morphology
Tachysurus platystomus is a striped Tachysurus, distinguished from the group's unstriped member (T. kyphus) by two continuous black longitudinal stripes running from head to caudal peduncle. Its caudal fin is only moderately forked rather than deeply forked, a trait it shares solely with its sister species T. heterofasciatus among the group's striped members — correlated, per the describing authors, with the pair's unusually high vertebral count.
The defining trait, and the source of its name, is mouth width: T. platystomus has the widest mouth (12.3–14.7% of standard length) of any species in the T. virgatus group. From T. heterofasciatus specifically it also differs in a shorter dorsal spine (15.7–20.3% of standard length, versus 19.1–24.4%) and a mid-lateral stripe with only a slight (rather than distinct) constriction at the posterior ends of the dorsal and adipose fins; its dorso-lateral stripe also stays well separated from the mid-lateral stripe, where in T. heterofasciatus the two approach or touch.
Across the type series, standard length ranges from about 1.35 in to 5.41 in, giving a described maximum size of roughly 5.4 in SL. As in all Tachysurus, the skin is entirely scaleless, and the dorsal and pectoral fins carry a locking, serrated spine.
Habitat
Tachysurus platystomus is known only from the Huangjiang River in Haifeng County, Guangdong Province, a coastal river draining into the South China Sea. The describing authors classify it as an obligate stream specialist, recorded exclusively in flowing stream habitat rather than the slower river mainstems used by some relatives in the group.
Stream-specialist habitat in this group is characterized as fast, well-oxygenated water over coarse gravel or boulder substrate, in contrast to the finer sand-and-silt, lower-oxygen mainstem channels used by some congeners. Notably, the paper singles out T. platystomus (along with its sister species T. pseudovirgatus) as occurring close to the Pearl River Delta — China's largest urban agglomeration — and attributes a marked population decline over the past decade to intensive urbanization pressure on this catchment. No temperature or pH data have been published specifically for T. platystomus.
Feeding
No diet information has been published for Tachysurus platystomus; the 2026 description is a taxonomic and phylogenetic study and does not record gut contents or foraging behavior. At the genus level, other Tachysurus are nocturnal benthic feeders that use their barbels to find invertebrate prey on the substrate after dark — a reasonable presumption, though not documented for this species.
Mating
No courtship or spawning behavior has been recorded for Tachysurus platystomus. Genus-level, Tachysurus species tend to be seasonal spawners with paired courtship, but nothing specific to this species has been reported.
Breeding
Breeding biology is entirely undescribed for Tachysurus platystomus. Presumed genus-level, Tachysurus are cavity or sheltered-substrate spawners with male egg-guarding, but this has not been confirmed for T. platystomus, which has never been kept or bred in captivity.
In the aquarium
Tachysurus platystomus is not in the aquarium trade. Described only in 2026 from a single, apparently declining river population in Guangdong, it has no husbandry record and, given the population pressure documented by its describers, would not be an appropriate candidate for wild collection even if demand existed. Any care notes offered here are genus-level speculation for reference only: other small Tachysurus generally do well as peaceful, nocturnal bottom-dwellers, and this species' fast-water, gravel-substrate habitat suggests it would need strong water movement and high dissolved oxygen if it were ever kept. Because Tachysurus skin is naked and scaleless, the genus is generally more sensitive to copper-based medications than scaled fish, and the locking dorsal and pectoral spines call for moving fish in a container rather than a net. None of this is confirmed for T. platystomus specifically.
Conservation
Tachysurus platystomus has not been formally assessed by the IUCN Red List and carries no official listing. In their conservation discussion, the describing authors specifically recommend Endangered status under IUCN Criterion B1a,b for T. platystomus, alongside T. pseudovirgatus — both known from a single location with a small population, situated close to the Pearl River Delta, China's largest urban agglomeration, and both showing pronounced population decline over the past decade that the authors attribute to intensive urbanization pressure. This is the authors' own preliminary assessment made in the description paper, not an official IUCN Red List listing, but it is among the more urgent conservation signals in the whole T. virgatus revision.
The authors note more broadly that this kind of taxonomic resolution has direct conservation consequences: a declining, range-restricted population that was effectively invisible while lumped into a single wide-ranging "T. virgatus" can now be recognized and, in their assessment, warrants protective attention that would not have been apparent under the old, broader species concept.