Taxonomy & naming
Triplophysa farwelli was described by the Indian ichthyologist Sunder Lal Hora in 1935 in the Journal of the Bombay Natural History Society, originally as Nemachilus farwelli, with its type locality given as the Helmand River, Afghanistan. Older literature and some database entries also render the original combination as Nemacheilus farwelli, a spelling-and-genus variant that circulated before the group was revised. The Catalog of Fishes — the standing authority for valid names — now places the species in Triplophysa, the genus into which the great majority of Central and South Asian stone loaches formerly held in Nemacheilus or Noemacheilus have been reassigned over the past few decades.
The species belongs to Nemacheilidae, the stone loaches or brook loaches, by species count the largest family of loaches and one of the largest families of freshwater fish overall. Triplophysa itself is a very large genus, radiating across the Tibetan Plateau, the Himalaya, and the river systems of Central and South Asia, with many species — this one included — known from a single drainage or even a single river.
Morphology
As with most Nemacheilidae, Triplophysa farwelli is a small, elongate, cylindrical loach built for holding position on the bed of running water: a rounded body tapering to a narrow caudal peduncle, a flattened belly, and a small subterminal mouth ringed with barbels for probing the substrate. Like other members of the family it carries the erectile suborbital spine typical of true loaches, tucked in a groove beneath the eye, and its skin is effectively naked — the scales, where present at all in this group, are tiny and deeply embedded rather than forming an obvious covering.
No maximum length, weight, or detailed morphometric description has been published in the sources available for this species, and no photographs or colour-pattern description could be confirmed. This is not unusual for a narrow-range Central Asian stone loach described nearly a century ago from a small series of museum specimens; many Triplophysa are known only from their original description and subsequent taxonomic notes rather than field guides or aquarium literature. Data is sparse, and any claim about its exact size or pattern would be guesswork.
Habitat
Triplophysa farwelli is endemic to the Helmand River drainage, an endorheic (closed) basin that rises in the mountains of central Afghanistan and drains southwest into the Sistan Basin wetlands straddling the Afghanistan–Iran border. Confirmed occurrence records place it in both Afghanistan and Iran within this system. As an inland stone loach of a mountain-fed drainage, it almost certainly lives in the flowing, oxygen-rich stretches typical of the genus — cool-to-subtropical running water over gravel and stone — though no site-specific temperature, pH, or flow data has been published for this particular species.
The Helmand system is markedly seasonal, fed by snowmelt from the Hindu Kush and subject to sharp swings between high spring flow and low, sometimes near-dry, summer conditions in its lower reaches. Fish restricted to this basin are adapted to that regime, but without direct field measurements for T. farwelli the water chemistry and thermal range given here should be read as inference from the wider genus and drainage rather than confirmed data for the species.
Feeding
No diet study has been published for Triplophysa farwelli specifically. Stone loaches in this genus are, as a rule, benthic micro-predators: they work the stream bed picking small invertebrates — insect larvae, worms and tiny crustaceans — from among gravel and stones, using their barbels to locate prey by touch and smell in flowing, often turbid water.
In the absence of species-specific data, that generalist benthic-invertebrate diet is the best-supported inference for this fish. There is no published information on how, or whether, it has ever been offered food in captivity.
Mating
Nothing has been published on courtship, spawning behaviour, or sexual dimorphism in Triplophysa farwelli. No description of the species records external differences between males and females, and no field or captive observations of reproductive behaviour appear in the available literature.
Breeding
There is no documented aquarium or captive breeding record for Triplophysa farwelli. Stone and brook loaches in Nemacheilidae as a group are, with rare exceptions, egg-scatterers that release eggs over gravel in fast-flowing water with no parental care, and are only occasionally bred by hobbyists even for the better-known species in the genus. Extrapolating that general pattern, T. farwelli's breeding mode is best described as egg-scattering with no parental care, but this species itself has essentially no breeding record — wild or captive — and the honest position is that reproduction has not been documented.
In the aquarium
Triplophysa farwelli does not appear to be established in the aquarium trade, and no husbandry account, tank report, or hobbyist care profile could be found for it. It should not be assumed to be available or suitable for a home aquarium on the strength of this entry.
If it is ever encountered, the safe starting assumptions for a Central Asian stream-dwelling Triplophysa apply: cool-to-moderate, clean, well-oxygenated, flowing water over a gravel or stone substrate, and — as with all nemacheilids — a near-scaleless body that is sensitive to copper and to full-strength medications, calling for gentle, reduced-dose treatment if disease occurs. Beyond those genus-level generalities, there is no specific guidance to offer for this species.
Conservation
Triplophysa farwelli has not been evaluated by the IUCN Red List and carries no conservation status here beyond Not Evaluated. It is known only from the Helmand River drainage of Afghanistan and Iran, a single endorheic basin under real and growing pressure from upstream damming, irrigation withdrawal, and periodic severe drought, all of which affect the Sistan wetlands the system feeds — but no population assessment, trend data, or threat analysis specific to this species has been published, so no risk category can be assigned beyond noting that narrow-range endemics of this drainage merit attention. There is no evidence this species is collected for the aquarium trade.