Taxonomy & naming
Paraschistura pasatigris was described in 2015 by Jörg Freyhof, Hamid Reza Sayyadzadeh, Hamid Reza Esmaeili and Matthias Geiger, part of a wave of species-level splitting that has reshaped Iranian and Middle Eastern nemacheilid loaches over the past two decades — genera such as Paraschistura, Oxynoemacheilus and Paracobitis have absorbed many fish once lumped under broad, catch-all names like Nemacheilus or Noemacheilus. The Catalog of Fishes, the standing authority for valid names, lists it in the family Nemacheilidae under the genus Paraschistura.
The species' taxonomic story does not end at its description, however. A 2019 revision of the genus (published in Zootaxa) reassessed several Iranian Paraschistura and treated P. pasatigris as a synonym of the earlier-described P. ilamensis. That later arrangement has not been adopted here, and the species is carried under its original, describing name — Paraschistura pasatigris — pending broader confirmation, consistent with keeping to the combination given in its original description rather than pre-empting an unsettled synonymy.
Morphology
Paraschistura pasatigris is a small stone loach, reported at a maximum of only about 2 in standard length, near the small end even for a family built of small fish. Like other nemacheilids it has the classic stone-loach build: an elongated, roughly cylindrical body, a flattened belly suited to hugging the streambed, small eyes set high on the head, and three pairs of barbels around a downturned mouth used to feel out food on the substrate.
Detailed colour pattern and fin-ray counts for this species are not covered in the sources available here, and given how narrowly it has been studied, it is best treated as data-sparse on fine morphological detail beyond its diminutive size and its placement in a family whose members are typically slim, barred or mottled bottom-dwellers built for clinging to cobbles in fast water.
Habitat
The species is known from a very restricted part of southwestern Iran: the type locality is the Bala River (Balarud) at Dezful, a tributary of the Dez River in Khuzestan Province, with further records from the Cholvar River (also in the Dez drainage) and Siah Gav in the Karkheh drainage. This places it within the Karun–Karkheh river system of the southern Zagros foothills, a region of clear, gravel- and cobble-bedded streams draining toward the Persian Gulf lowlands.
No site-specific temperature or pH readings for P. pasatigris are recorded in the sources consulted here. Stone loaches as a family are creatures of clear, fast-flowing, well-oxygenated water over gravel and pebble substrate, and closely related nemacheilids from comparable Middle Eastern and European streams are typically found in cool-to-moderate flowing water — conditions this species almost certainly shares, but the specific figures for this population have not been published and should not be guessed at.
Feeding
FishBase records a trophic level of about 2.8 for Paraschistura pasatigris, consistent with the low-level micro-predator niche typical of the Nemacheilidae: a bottom-forager taking small aquatic invertebrates, insect larvae and other tiny prey items picked from among gravel and cobbles in flowing water, rather than a grazer or true omnivore.
No aquarium feeding record exists for this species, since it has no documented history in the hobby. Based on its family and trophic level, a diet built around small live and frozen foods — bloodworm, daphnia, brine shrimp and similar sinking items — would be the expected way to meet its needs, mirroring how its stone-loach relatives are fed when kept.
Mating
Nothing specific to Paraschistura pasatigris has been documented about courtship or spawning behaviour; the species is far too little-studied for that. Stone loaches in general are egg-scatterers, and where nemacheilid spawning has been observed at all, it typically involves a brief pairing or chase over gravel or fine substrate in fast-flowing water, with no lasting pair bond and no nest.
Given the total absence of published breeding or sexing data for this species, any statement about dimorphism or courtship specific to P. pasatigris would be speculation. It is fairest to say this is an unstudied aspect of an unstudied fish.
Breeding
As with the great majority of stone and brook loaches, Paraschistura pasatigris is not known to have been bred in the aquarium, and there is no record of it having been kept in the hobby at all. The expected mode, based on its family, is egg-scattering over gravel in fast-flowing water with no parental care of eggs or fry — the standard nemacheilid pattern — but this has not been directly observed or documented for this particular species.
Given how narrow its known range is and how sparse the literature on it remains, breeding biology should be treated as an open question rather than a settled fact. Any keeper attempting to reproduce it would be working from family-level inference, not from a documented protocol.
In the aquarium
Paraschistura pasatigris has no established presence in the aquarium trade, and nothing here should be read as an endorsement of collecting or keeping it — it is included for completeness as a described, valid species rather than as a recommended aquarium fish. If it were ever kept, its small size (under 2 in) and its place in a family of cool-water, fast-flow specialists would argue for a modestly sized tank with a gravel or fine-cobble substrate, strong water movement, high dissolved oxygen and clean, clear water, mirroring the conditions of the Iranian foothill streams it comes from rather than a warm, still community setup.
As a nemacheilid, it should also be assumed to share the family's general sensitivities until shown otherwise: stone loaches tend to have reduced scalation compared to fully scaled fish and, like other scaleless-leaning loaches, can be more sensitive to copper-based and full-strength medications than typical community fish, warranting caution and reduced dosing if any treatment is ever needed.
Conservation
Paraschistura pasatigris has not been formally assessed on the IUCN Red List and is recorded here as Not Evaluated. Its known range is extremely narrow — a handful of streams in the Dez and Karkheh drainages of Khuzestan Province, Iran — the kind of restricted, single-region distribution that typically leaves a species vulnerable to local pressures even without a formal assessment.
As a range-restricted stream endemic in an actively developing part of southwestern Iran, where water extraction, damming and agricultural runoff affect many Zagros foothill drainages, its status deserves a proper IUCN evaluation. In the meantime, the honest picture is one of a data-poor species: too little studied to assign a meaningful conservation category, and not documented in trade at all.