Taxonomy & naming
Tachysurus bailongensis was described in 2026 by Weihan Shao and E Zhang, with co-authors Xingwei Cai and Tan Duc Nguyen, in an integrative-taxonomy paper published in the journal Animals that dismantled the wide-ranging nominal species Tachysurus virgatus (Oshima, 1926) into ten separate lineages. Specimens across the historical range of T. virgatus — coastal south China and central-northern Vietnam — proved to fall into distinct, reciprocally monophyletic mitochondrial lineages despite near-identical external appearance, a pattern the authors describe as pervasive cryptic diversity driven by morphological conservatism combined with isolation across independent coastal drainages.
T. bailongensis belongs to Bagridae, genus Tachysurus, and within that genus to the T. virgatus species group. Phylogenetically it falls in Clade I, where it forms a well-supported sister pair with T. furcatus of central Vietnam — the two differing by only 1.5% in cytochrome b sequence despite occupying different countries and, per the authors, showing substantial differences in body proportions, color pattern and ecology.
The holotype (FANGC12597, 2.8 in standard length) was collected by Weihan Shao in September 2021 from the Fangcheng River at Naguo Town, Fangchenggang City, a coastal river of the Beibu Gulf drainage in the Guangxi Zhuang Autonomous Region. Paratypes came from the same river and from the nearby Jiangping River at Dongxing City. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) records Tachysurus bailongensis Shao & Zhang, 2026 as the valid name, with no synonyms.
Morphology
Tachysurus bailongensis carries the striped Tachysurus pattern: two continuous black longitudinal stripes running from head to caudal peduncle, a deeply forked caudal fin with narrow, straight-edged lobes, and the standard three pairs of barbels of the genus. Like most members of its immediate clade (with T. pseudovirgatus, T. virgatus, T. trimaculatus and T. furcatus) it has a prominent notch in the dorso-lateral stripe behind the dorsal fin and a mid-lateral stripe that runs uniform and unconstricted rather than tapering.
What sets it apart is a combination of a shallower head (depth 53.4–59.1% of head length, versus 58.6–71.1% in its closest relatives) and a narrower head (width 59.8–68.5% of head length), together with a dorso-lateral stripe that is broadly connected to the black blotches on the operculum — a connection absent in most of its relatives except T. trimaculatus, from which it differs by a broader (rather than slight-or-absent) join between the dorso- and mid-lateral stripes just in front of the dorsal fin.
Across the type series, standard length ranges from about 1.67 in to 3.02 in, giving a described maximum size of roughly 3 in SL. As in all Tachysurus, the skin is entirely scaleless, and the dorsal and pectoral fins carry a locking, serrated spine.
Habitat
Tachysurus bailongensis is known from the Fangcheng and Jiangping rivers, two coastal rivers flowing into the Beibu Gulf in the Guangxi Zhuang Autonomous Region of southern China. It is one of only two species in the T. virgatus group — along with true T. virgatus itself — that the describing authors class as a habitat generalist rather than a specialist: juveniles occur mainly in upper stream reaches, while adults are largely restricted to the rivers' main channels, a pattern the authors note may reflect an ontogenetic shift in habitat use, though they caution that firm evidence for that shift is still lacking.
Generalist species in this group are reported to occupy the middle-to-upper reaches of smaller coastal rivers, positioned closer to montane stream conditions and over gravel-dominated substrate, in contrast to the sand-and-silt lower reaches used by strict mainstem specialists. No temperature or pH data have been published for T. bailongensis specifically; its native rivers lie in the subtropical coastal zone of southern China.
Feeding
No diet information has been published for Tachysurus bailongensis; the 2026 description is a taxonomic and phylogenetic study and does not report gut contents or feeding behavior. At the genus level, other Tachysurus are nocturnal benthic feeders that use their barbels to locate invertebrate prey on the riverbed after dark — a reasonable presumption for this species, but not a documented fact.
Mating
No courtship or spawning behavior has been recorded for Tachysurus bailongensis. 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 bailongensis. Presumed genus-level, Tachysurus are cavity or sheltered-substrate spawners with male egg-guarding, but this has not been confirmed for T. bailongensis, which has never been kept or bred in captivity.
In the aquarium
Tachysurus bailongensis is not in the aquarium trade. Described only in 2026 from type specimens taken from two Guangxi coastal rivers, it has no husbandry record. Any care guidance offered here is genus-level speculation for reference only: other small Tachysurus generally do well as peaceful, nocturnal bottom-dwellers over soft sand with caves or pipe shelters, fed sinking foods after the lights go out. 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. bailongensis specifically.
Conservation
Tachysurus bailongensis has not been assessed by the IUCN Red List and carries no official conservation status. In their discussion of conservation implications, the describing authors grouped the two habitat generalists of the T. virgatus group — T. virgatus itself and T. bailongensis — with the species they recommend for a Least Concern designation, based on extents of occurrence in the range of roughly 5,000–30,0 mi² for that broader river-mainstem-associated category and no documented population decline. This is the authors' own preliminary recommendation from the description paper, not a formal IUCN listing, and no dedicated population survey of T. bailongensis has been published.
The authors more broadly emphasize that recognizing the T. virgatus group's true species diversity is itself a conservation contribution: populations that were previously invisible under one widespread species name can now be tracked and, where warranted, protected individually.