Taxonomy & naming
The species was first described by Peter Humphry Greenwood in 1976 as Noemacheilus smithi, based on specimens from a natural well near the Baq-e-Loveh Oasis in Iran's Zagros Mountains. It was later shifted into Paracobitis smithi as the old wastebasket genus Noemacheilus was broken apart, before a 2016 revision (published in Zootaxa) erected the genus Eidinemacheilus for it, distinguished by a strongly reduced head lateral-line canal system, 7+7 branched caudal-fin rays, and its unique troglomorphic anatomy — no eyes, no pigment, no scales. The genus currently holds just two known species, E. smithi and E. proudlovei from Iraqi Kurdistan.
It belongs to Nemacheilidae, the stone and brook loaches, the most species-rich family of true loaches (Cobitoidea), whose members are mostly small benthic fish of cool, clear, fast-flowing streams across Eurasia. E. smithi is an extreme departure from that pattern — a permanent cave-dweller — and the Catalog of Fishes, the authority for valid names, lists it as Eidinemacheilus smithi (Greenwood, 1976).
Morphology
This is a small loach, reaching only about 2 in in total length. Its body is elongated with a compressed cross-section, typical of the nemacheilid build, but every trace of surface adaptation has been stripped away by life underground: the skin is whitish to pink and essentially without pigment, and the eyes are absent entirely, a classic troglomorphic (cave-adapted) condition seen convergently in blind cavefish around the world.
As in other stone and brook loaches, the head carries a system of sensory canals and pores that substitute for vision in the dark, though in this species that lateral-line canal system is itself notably reduced compared to surface relatives — one of the technical characters used to separate Eidinemacheilus from other nemacheilid genera. Like most of its family it lacks the erectile suborbital spine of the botiid loaches, and its near-scaleless skin — a trait shared across the true loaches — makes it, in principle, sensitive to medication, though this is essentially a moot point given it is not a fish anyone keeps.
Habitat
Eidinemacheilus smithi is a stygobitic (obligate groundwater-dwelling) fish, known from a natural well at Kaaje-Ru near the Baq-e-Loveh Oasis and from a cave system, within the Karun River drainage of the Iranian Zagros Mountains. A second locality, Tuveh Spring, roughly 19 mi south of the original cave, was documented in 2022, indicating the species occupies a connected karst aquifer system rather than a single isolated pool. It lives permanently in subterranean pools and springs at high altitude in this range, never seen in surface daylight.
The water in these aquifers is presumably cool and clear, typical of karst spring systems, though little has been published on its precise chemistry. This is unambiguously a cool, subtropical groundwater habitat, not a warm lowland river — the Zagros sit at high elevation, and the species is entirely dependent on the stability of a fragile, enclosed aquifer system rather than an open flowing stream.
Feeding
Almost nothing has been published on the natural diet of Eidinemacheilus smithi, and the cache of available sources does not describe it. As a small benthic cavefish it most likely forages by touch and chemoreception for whatever small invertebrates and detritus wash into or persist within its subterranean pools — the sparse food base typical of cave ecosystems, which generally support only a fraction of the biomass of surface streams. This is an honest gap: the species' feeding ecology is data-sparse, and no aquarium feeding regime exists because the fish is not kept.
Mating
No information on courtship, sexing, or mating behaviour in Eidinemacheilus smithi appears in the available literature. Cave-dwelling fish generally reproduce at low intensity in a resource-poor, dark environment, and reproductive biology for stygobitic nemacheilids worldwide is very poorly documented. Nothing specific can be said here without guessing, so this remains an open question for this species.
Breeding
As with most stone and brook loaches, Eidinemacheilus smithi is presumed to be an egg-scattering species with no parental care, following the general pattern for Nemacheilidae — but this has not been directly documented for the species itself. It has never been bred, or even kept, in the aquarium; it is not a hobby fish, and no captive-breeding data exists. Given its extreme habitat specialisation to permanently dark, stable subterranean water, any assumption about breeding triggers based on surface-stream relatives would be unfounded speculation, so the honest position is simply that its reproductive biology is unstudied.
In the aquarium
Eidinemacheilus smithi is not an aquarium fish. It does not appear in the ornamental trade, has no established husbandry record, and its extreme rarity, tiny known range, and total dependence on a stable groundwater habitat make collection for the hobby both impractical and ecologically irresponsible. Blind, unpigmented cavefish of this kind are exceptionally difficult to sustain outside their native aquifer, needing darkness and precise, stable water conditions that are hard to replicate. There is no honest care guidance to give beyond this: the species belongs in its cave system, not in a tank.
Conservation
Eidinemacheilus smithi is assessed as Vulnerable (VU) by the IUCN Red List, first evaluated in 1996. The species has an extremely restricted range, known only from a small number of connected karst wells, springs and cave pools in the Karun–Dez basin of the Iranian Zagros Mountains. The primary threat is groundwater over-extraction: unsustainable water management and falling aquifer recharge in the region risk drying out the springs and wells the species depends on, which would be catastrophic for a fish with nowhere else to go.
As a strict groundwater endemic with no presence in the aquarium trade, this species faces no collection pressure — its entire conservation story is about water management in one of Iran's karst aquifer systems. The 2022 discovery of a second population at Tuveh Spring is a modest positive sign that the species' range within the aquifer network may be somewhat broader than once thought, but its fundamental vulnerability to groundwater decline remains unchanged.