Taxonomy & naming
Nemacheilus binotatus was described by the American ichthyologist Hugh McCormick Smith in 1933 from Mekhan, a tributary of the Meping River southwest of Doi Suthep in northern Thailand. It belongs to the family Nemacheilidae, the stone or brook loaches — by species count the largest family of loaches, spread across Eurasia from Anatolia and the Middle East to the Himalaya, Southeast Asia and East Asia.
The genus Nemacheilus has been heavily revised since Smith's time: many species once placed here, or in the old catch-all Noemacheilus, have since been redistributed into Schistura, Triplophysa, Barbatula and other segregate genera as the family's taxonomy has been untangled. Nemacheilus binotatus itself has retained its original combination; the Catalog of Fishes, the standing authority for valid names, continues to list it as Nemacheilus binotatus Smith, 1933.
Morphology
This is a small loach, reaching only about 1.5–2 in standard length — modest even by the standards of a family built from small fish. Like other members of the Nemacheilidae it has an elongate, sub-cylindrical body, a flattened underside suited to gripping the streambed, and paired barbels around the mouth used to feel out food in the substrate.
As in many nemacheilids, the skin is essentially naked or carries only very fine, deeply embedded scales, and an erectile suborbital spine sits in a groove below the eye — a defensive structure shared across the true loaches. Both features matter in the aquarium: the near-scaleless skin makes stone loaches sensitive to medications, and the spine can snag in a net, so a fish should be moved in a container rather than lifted in mesh.
Habitat
Nemacheilus binotatus is confined to western and central Thailand, recorded from the Mae Klong and Chao Phraya river basins. It lives in shallow, flowing sections of stream with sandy or gravelly substrate and accumulations of organic debris — the kind of clear, moving headwater and tributary water typical of stone loaches generally.
Water at known sites runs 73–79 °F with a pH of roughly 6.0–7.5: cool-to-moderate, well-oxygenated, flowing fresh water, not the warm, still blackwater some other loach groups favour. Beyond the basin-level distribution and these habitat notes, detailed population and ecological data for the species are sparse, consistent with its Data Deficient status.
Feeding
As a micro-predator of the streambed, N. binotatus forages for small insects, worms, crustaceans and zooplankton picked from sand, gravel and leaf litter in flowing water. This is a hunting, not a grazing, diet — it targets live prey rather than scraping algae or biofilm.
In the aquarium it takes live and frozen foods readily — Daphnia, Artemia and bloodworm are all reported to work well — and is best offered a varied, meaty, sinking diet rather than relying on flake, which it may ignore in favour of foods that better match its natural prey.
Mating
No courtship or spawning behaviour has been documented for this species. Data on reproduction in Nemacheilus binotatus is essentially absent from the literature available, which is unsurprising for a small stream endemic that has drawn little targeted study.
Breeding
Breeding is unrecorded in the aquarium for this species. Stone and brook loaches in general are egg-scatterers that release eggs over gravel or among stones in fast water with no parental care, and spawning is rarely observed even in the wild for most Nemacheilidae; N. binotatus fits that pattern rather than being any kind of exception. Prospective keepers should treat it as a species to observe and enjoy, not one they can expect to propagate.
In the aquarium
Seriously Fish recommends a minimum tank of around 60×12 in with strong flow — on the order of four to five times the tank volume per hour — to replicate the moving-water conditions this species needs. It is social and peaceful, doing best in a group of four or more, and should be given a sandy or fine-gravel substrate it can sift and rest on, plus some structure such as smooth stones and driftwood.
Because it is essentially scaleless, it is sensitive to copper and to full-strength doses of many medications, so any treatment should be approached cautiously, at reduced dose where possible. Water should be kept cool-to-moderate (around 73–79 °F) rather than tropical-warm, with good oxygenation and a gentle current running through the tank at all times — a static, warm setup is the wrong environment for this fish.
Conservation
The IUCN Red List assessed Nemacheilus binotatus as Data Deficient in its 2022.2 assessment (taxon ID 166053), reflecting how little is known about the species' population size, trends or specific threats. This is common among small-range Nemacheilidae endemics restricted to a handful of streams, where survey effort is limited.
No specific threats or trade pressures are documented for this species in the sources available. Given its confinement to particular river systems in Thailand, habitat changes affecting the Mae Klong and Chao Phraya basins — such as water extraction, pollution or stream modification — would be the plausible long-term risks, though this remains inference rather than a documented finding.