Taxonomy & naming
Nemacheilus anguilla was described by the Scottish zoologist Nelson Annandale in 1919, placing it in the genus Nemacheilus — one of the oldest and largest genus names in the stone-loach family Nemacheilidae. The family has been heavily revised since, with many species once lumped under Nemacheilus or the older spelling Noemacheilus later moved into Schistura, Triplophysa, Barbatula and other genera as the Catalog of Fishes and molecular work reshuffled the group; N. anguilla has remained in Nemacheilus through those revisions.
The species epithet anguilla is Latin for "eel," a fitting name for a loach with the elongated, faintly serpentine body typical of the genus, and it shows up in the common trade name "eel loach." Nemacheilidae itself is the largest loach family by species count, the bulk of them small, drab, stream-bound fish that are far less documented than their showier botiid and cobitid relatives.
Morphology
This is a small, elongate loach, reported to reach only around 2 in in standard length — modest even by stone-loach standards. Like other Nemacheilidae it carries the family's near-scaleless, faintly slippery skin, a trait that matters far more for husbandry than for looks, since it leaves the fish highly sensitive to medication and general water disturbance. Where present in the genus, an erectile suborbital spine sits beneath the eye, though detailed anatomical description for this particular species is thin in the available literature.
Beyond the basic size and family-typical build, published morphological detail on N. anguilla is sparse — much of what is documented comes from FishBase's brief summary and Annandale's original description rather than a modern redescription, so specific counts of fins, barbels or colour pattern should be treated as provisional rather than exhaustively confirmed here.
Habitat
Nemacheilus anguilla is endemic to the Western Ghats of southern India, a mountain range recognised as one of the world's biodiversity hotspots and the source of a great many narrow-range freshwater endemics. It occurs in streams running over pebble and sandy substrates in the hill country of the region, the classic setting for a Nemacheilidae species: cool-to-moderate, clear, moving water rather than still or blackwater habitat.
In the aquarium the reported range is roughly 72–79 °F with a pH of about 6.0–7.5, in water with good flow — figures consistent with a foothill stream loach rather than a lowland tropical one. It should be given moderate-to-strong current and high dissolved oxygen; it is not a fish for a warm, still community tank.
Feeding
As a bottom-dwelling stone loach, N. anguilla is best understood as a small micro-predator, picking small invertebrates, insect larvae and other tiny prey items from among the pebbles and sand of its home streams — the standard foraging mode across Nemacheilidae. Specific dietary studies for this species have not been located, so this picture is inferred from its family and habitat rather than confirmed field data.
In the aquarium it has been kept on sinking catfish pellets along with frozen foods such as mosquito larvae, brine shrimp and daphnia — foods that mimic the small live and drifting prey it would take in the wild. As with most loaches, it may largely ignore flake food floating at the surface, so sinking, meaty foods delivered near the substrate are the reliable way to feed it.
Mating
No courtship or spawning behaviour has been documented for Nemacheilus anguilla in the available literature or trade sources. Data on this species is genuinely sparse beyond its original description and a brief FishBase and hobbyist summary, and nothing specific is known about how males and females differ in appearance or how pairs might form.
What can be said follows from its family: Nemacheilidae species that have been observed spawning are typically egg-scatterers that pair or group-spawn in flowing water with no courtship display beyond a brief chase, but this has not been specifically confirmed for N. anguilla.
Breeding
There are no reported aquarium spawnings of Nemacheilus anguilla, and reproduction in captivity is essentially unknown. This fits the broader pattern for stone and brook loaches: most Nemacheilidae species scatter eggs over gravel and stones in fast-flowing water with no parental care, and very few have ever been deliberately or accidentally bred by hobbyists.
Given the complete absence of breeding reports, the honest assessment is simply that this is a species that is collected from the wild for the trade rather than propagated, and anyone hoping to spawn it should expect to be working from first principles rather than an established protocol.
In the aquarium
Nemacheilus anguilla suits a small, cool-to-mild, well-oxygenated stream-style aquarium rather than a standard tropical community tank. Water in the range of roughly 72–79 °F with a pH of 6.0–7.5 and good current, over a sand-and-pebble substrate, mirrors its Western Ghats streams; strong filtration or a powerhead to maintain flow and oxygenation is worthwhile given its origin in fast hill water.
Because it is scaleless-skinned like other Nemacheilidae, it is sensitive to copper-based medications and full-strength treatments generally, so any medicating should be done cautiously and at reduced dose. It will take sinking pellets and frozen foods readily, and given its small adult size of around 2 in it does not need a large tank, but it does need clean, current-rich, well-oxygenated water and should not be kept warm and still. As with most small loaches, a group and plenty of cover among stones is likely to suit it better than being kept alone, though specific social-behaviour data for this species has not been documented.
Conservation
Nemacheilus anguilla is assessed by the IUCN Red List as Least Concern, per a 2011 assessment. It is endemic to the Western Ghats, where it lives in streams with pebble and sandy substrates; FishBase notes that the species is collected for the aquarium trade in a small way, and that a plausible pressure on some of its waters is pollution linked to pilgrim visitation near temple sites in the region rather than any large-scale threat.
As with many small range-restricted Western Ghats endemics, its Least Concern status reflects a currently stable picture rather than an absence of local pressures, and given how little has been published on its population trends beyond the original assessment, ongoing habitat quality in its home streams is worth watching rather than assuming settled.