Taxonomy & naming
Neoeucirrhichthys maydelli was described in 1968 by the Romanian ichthyologist Petru Bănărescu and Romanian-French colleague Theodor Nalbant. It is the only species placed in the genus Neoeucirrhichthys, a monotypic status that in loaches usually signals either a genuinely isolated evolutionary lineage or simply a poorly-collected, poorly-studied one — in this case both are likely true, given how few surveys have reached its home streams.
The species sits in the family Cobitidae (the spined loaches) and subfamily Cobitinae, the same lineage that includes the temperate European Cobitis and Sabanejewia and the East Asian dojo loach Misgurnus, though N. maydelli itself belongs to the tropical South Asian branch of the subfamily. The Catalog of Fishes is the authority for the valid combination; nothing here has been recombined into another genus, and the name Neoeucirrhichthys maydelli stands as originally published.
Morphology
As a member of Cobitidae, the Goalpara loach carries the family's signature feature: an erectile, two-pronged spine tucked in a groove below each eye, which the fish can flick out when handled or threatened. Its skin is effectively naked to the touch, covered only in tiny, deeply embedded scales — a trait shared across the family that makes these fish notably sensitive to medication and to rough handling.
The species' single best-documented anatomical feature is unusual even by loach standards: in mature males, the median rays of the pectoral fin are thickened and broadened, a form of pectoral sexual dimorphism that GBIF distribution notes flag as unique within Cobitidae. Beyond that, published size and general body-proportion data are sparse; no confirmed maximum length figure could be traced to a reliable source, so none is asserted here. It is presumed, based on the ecology of small tropical stream-dwelling Cobitinae, to be a modestly sized fish.
Habitat
Neoeucirrhichthys maydelli is native to the Brahmaputra river system of Assam, India — the type locality — and to tributaries of the Surma river in Sylhet district, Bangladesh, most specifically the Lubachhara stream. These are fast-flowing, cool-to-warm tributary streams running over limestone substrate in the hill country bordering Meghalaya, a very different setting from the sluggish lowland canals many South Asian loaches tolerate.
This is a tropical species, not one of the coldwater Eurasian spined loaches — it belongs to the warm-water South Asian branch of Cobitinae rather than to temperate genera like Cobitis or Misgurnus. The Lubachhara population's habitat has been severely compromised: each winter the river reportedly turns a toxic deep blue from limestone-mine and cement-factory discharge upstream in Meghalaya, and the species is feared nearly or fully extirpated from that particular water.
Feeding
Like other Cobitidae, the Goalpara loach is a sand-sifting benthic omnivore, working soft substrate for worms, insect larvae, small crustaceans, molluscs and detritus. No species-specific dietary study appears to exist, but this feeding mode is conserved strongly enough across the family that it can be stated with confidence for N. maydelli as well.
In practice this means the fish needs a soft, sand or fine-gravel bed to forage naturally rather than a bare-bottomed or coarse-gravel setup; sifting through the substrate is not incidental behaviour but the way this group actually finds its food.
Mating
The unusual thickened, broadened median pectoral-fin rays reported in males are presumably a sexual signal or a physical aid used in courtship or spawning contact, though no published account describes their exact function or how the fish deploys them. No other reliable external sexing characters for this species have been documented.
No field or aquarium account of courtship or spawning behaviour for N. maydelli could be traced. Based on the conserved reproductive biology of Cobitidae generally, spawning is presumed to follow the family's typical pattern of scattering eggs rather than pairing off to guard a site, but this is an inference from family-level biology, not a direct observation of this species.
Breeding
No aquarium breeding of Neoeucirrhichthys maydelli has been documented, and the species does not appear in the hobby trade in any meaningful volume. Based on its place in Cobitidae, the expected mode is that of a spined/pond loach: an egg-scatterer releasing adhesive eggs among plants or vegetation, typically around spring, with no parental care afterward.
It is worth being clear about where that expectation comes from: several temperate Cobitidae — Cobitis, Sabanejewia, and the dojo/weather loach Misgurnus — have been pond- or tank-spawned by hobbyists and researchers, while the tropical South and Southeast Asian members of the family, including genera like Acantopsis and Lepidocephalichthys, generally have not. N. maydelli falls firmly in that second, un-bred camp. There is no cave-guarding male and no mouthbrooding in this family — any such account would be describing a different fish entirely.
In the aquarium
Neoeucirrhichthys maydelli is essentially unknown in the aquarium hobby; it is not a fish a keeper is likely to encounter for sale, and this profile should be read as a natural-history sketch rather than a stocking guide. Were it ever kept, the family-level cues are worth carrying over: a soft sand substrate for sifting, cool-to-moderate flowing, well-oxygenated water reflecting its hill-stream tributary origin, and gentle handling and medication given its near-scaleless, spine-bearing anatomy — full-strength doses and copper-based treatments are best avoided or halved, as with other Cobitidae.
Because almost nothing has been published on husbandry specifics for this species, anyone who did obtain wild-collected specimens would be working from family-level inference rather than species-specific guidance — all the more reason to treat any individual with caution rather than assumption.
Conservation
The picture here is a genuine discrepancy between two assessments made years apart at different scales. The global IUCN Red List currently lists Neoeucirrhichthys maydelli as Least Concern (2020), but the Bangladesh National Red List (2015) rates the country's population Critically Endangered — and the more recent, more local picture is troubling. The type locality of the Bangladesh population, the Lubachhara stream in the Surma drainage, is reported to turn toxic each winter from limestone-mining and cement-factory discharge originating upstream in Meghalaya, India, and the species is feared largely or entirely extirpated there.
The global Least Concern rating likely reflects the wider Brahmaputra-drainage range in Assam rather than any reassessment of the Bangladesh decline, and it should be read with that caveat rather than taken as reassurance. As a monotypic genus restricted to a small set of hill streams straddling an international border with active industrial pollution, N. maydelli is a clear case where local, on-the-ground data paints a far more urgent picture than a stale global category.