Taxonomy & naming
Yasuhikotakia longidorsalis was described by Taki and Doi in 1995 from specimens collected in the Mekong river system. The parenthetical authority notation reflects the convention that the species was originally placed in a different genus before being moved to Yasuhikotakia — a monophyletic grouping of mid-sized botiid loaches that also includes better-known species such as Y. modesta, Y. morleti, and Y. lecontei. The Catalog of Fishes (Eschmeyer, CAS), the authority for valid fish names, lists Yasuhikotakia longidorsalis as the accepted combination.
Within the genus, Y. longidorsalis is placed in the modesta-group based on shared anatomical and pigmentation characters. The modesta-group species are distinguished from other Yasuhikotakia by body proportions and colour pattern details, though the group's internal relationships and the full extent of Y. longidorsalis's range within the Mekong basin remain incompletely resolved. The species' extreme rarity in hobbyist collections and the trade has kept it outside the scope of most popular-literature accounts, and published morphological data are limited primarily to the original description and FishBase records.
Morphology
Yasuhikotakia longidorsalis is a small, moderately slender botiid loach reaching a reported maximum of 3 in standard length — making it one of the smaller members of its genus. The most distinctive external feature that gives it its name is the dorsal fin, which is notably long and high, with nine to ten branched rays, a count on the upper end for the genus. The flanks are marked with 13 to 18 narrow, brownish, irregularly spaced vertical bars that can appear as broken or fused blotches depending on the individual and its mood; a broad dark bar sits across the caudal peduncle, and small brownish spots scatter across the lobes of the caudal fin.
In common with all botiid loaches, Y. longidorsalis carries a sharp, erectile suborbital spine in a groove beneath each eye. This spine can be flicked outward as a defence and will readily snag a net; fish should be moved with a container rather than lifted in mesh to avoid injury to the fish and to the handler. The body is covered in minute, deeply embedded scales that leave the skin feeling naked — a characteristic that makes the species, like all near-scaleless loaches, sensitive to medications that absorb through the skin.
Habitat
Yasuhikotakia longidorsalis is endemic to the Mekong river system of mainland Southeast Asia. iNaturalist occurrence records confirm its presence within this drainage, and the IUCN/CMS briefing classifies it as a full migrant within the Mekong system — consistent with the botiid pattern of seasonal movement between spawning and feeding grounds as flood cycles advance and recede. The precise countries within the Mekong basin where the species occurs are not fully documented in available sources, but the Mekong drainage spans Laos, Thailand, Cambodia and Vietnam, all of which are candidate range states.
The Mekong and its tributaries carry warm, well-oxygenated, generally soft-to-neutral fresh water. Like other modesta-group Yasuhikotakia, this species is intolerant of organic waste accumulation and should never be introduced into a biologically immature aquarium system. It is a strictly freshwater, tropical-warm fish — not brackish, not coldwater.
Feeding
Yasuhikotakia longidorsalis is an omnivore, like its botiid relatives, with an appetite focused on small invertebrates. In the aquarium it will accept sinking pellets, algae wafers, earthworms, frozen bloodworms, mysis shrimp and chopped cocktail shrimp, along with quality sinking flake food. A varied diet that includes both live or frozen and prepared foods is ideal for maintaining condition.
Botiid loaches are effective, if not gentle, snail hunters — Y. longidorsalis can be expected to reduce pest snail populations in a well-stocked tank, crushing smaller snails with the pharyngeal teeth in the same manner as its congeners. Because it is a group-living fish with a social hierarchy, feeding should be generous enough that subordinate individuals receive their share; supplementing with a feed after lights-out suits the species' partly nocturnal foraging habit.
Mating
Published data on the reproductive biology of Yasuhikotakia longidorsalis are sparse, and no verified aquarium spawning has been documented. In the wild, the species is classified as a full migrant in the Mekong system, which implies that it undertakes seasonal breeding migrations tied to the monsoon flood cycle — as the river rises, fish move into shallower, faster-flowing or flooded tributary waters to reproduce, returning to larger channels as waters recede.
Sexual dimorphism is not described in available sources; as in other Yasuhikotakia, females are likely to be plumper-bodied when gravid, but reliable external characters for routine sexing have not been reported. The combination of an incomplete understanding of reproductive cues, the migration trigger required, and the species' near-absence from the trade means that pairing and conditioning specimens for spawning under home aquarium conditions is not a realistic prospect.
Breeding
Yasuhikotakia longidorsalis has not been bred in the home aquarium, and there is no realistic expectation that it will be. As a botiid loach it is an egg-scatterer with no parental care: in the wild, ripe fish shed eggs into flowing water during the flood migration and leave them to their fate. The trigger for spawning is tied to the seasonal hydrology of the Mekong — changes in flow, water volume, temperature and chemistry that accompany the monsoon floods — conditions that are not reproducible in a domestic tank.
Commercial botiid production for the hobby trade relies on hormone induction, as is used for the clown loach and other species; there is no indication that Y. longidorsalis has ever entered commercial production at all. The species has reportedly never been available in the aquarium trade, so the question of captive breeding is largely academic. Keepers who obtain specimens should regard them as display and study fish, not potential breeding projects.
In the aquarium
Yasuhikotakia longidorsalis is reported to require a large tank with excellent filtration and regular water changes — a demand consistent with the modesta-group's known sensitivity to organic waste. It must never be introduced into a biologically immature system. Water parameters from available sources indicate a tropical-warm preference: temperature 79–86 °F (79–86 °F), pH 6.5–7.5, and hardness up to approximately 12 °dH. Flow and oxygenation should be good, as with all botiid loaches.
A sandy substrate is strongly preferred: Y. longidorsalis is an enthusiastic digger, and fine sand protects the delicate barbels that botiids use to probe the bottom. Dim lighting suits its shy, partly nocturnal temperament, and numerous hiding places — caves, smooth rock structures, driftwood — are essential. The species is reported to be territorial and incompatible with small or timid tankmates; suitable companions are other assertive loaches of similar size or robust, swift barbs.
As a near-scaleless botiid, it is sensitive to copper and to full-strength doses of many aquarium medications, and yet is likely to be among the first fish in a tank to show signs of ich or other external parasites. Medications should be applied at reduced dose with careful monitoring, and copper-based treatments should be avoided. Like all botiid loaches, it is obligate-social and must be kept in a group of five or more to express normal behaviour; solitary or paired individuals become stressed, skittish or aggressive.
Conservation
Yasuhikotakia longidorsalis is assessed as Data Deficient on the IUCN Red List, a designation confirmed in the 2024 IUCN/CMS briefing on freshwater fishes of potential conservation interest. Data Deficient does not mean that the species is not at risk; it means that the available information is insufficient to evaluate its status against IUCN criteria. Given its apparent rarity in collections, limited distribution data, and dependence on the seasonal hydrology of the Mekong system, concern is warranted.
The Mekong is one of the world's most heavily dammed river systems, and the proliferation of large hydroelectric dams on the mainstream and major tributaries has profoundly altered seasonal flood pulses, sediment regimes and migratory corridors. For a species classified as a full migrant in this system, disruption of seasonal migrations by dam barriers and altered hydrology represents a plausible threat, even if population impacts have not been quantified. Deforestation and sedimentation of tributary habitats add further pressure. The species has apparently never entered the aquarium trade, so collecting pressure is not a documented concern, but the lack of trade interest also means there is no commercial impetus to study or monitor it.