Taxonomy & naming
Cobitis linea was described by the Austrian ichthyologist Jakob Heckel in 1847, one of several spined loaches he named from material collected in what is now Iran. It remains in its original genus, Cobitis, the type genus of the family Cobitidae and the group after which the family's suborbital spine is often discussed. The Catalog of Fishes — the standing authority for valid fish names — recognises Cobitis linea as a distinct species.
The genus Cobitis has been reshuffled repeatedly as ichthyologists have split the old broad "spined loach" concept along genetic and morphological lines, spinning off genera such as Sabanejewia elsewhere in its range. Cobitis linea has not been caught up in any such split and is treated straightforwardly under its original combination; it is not to be confused with the more widely known European spined loach, Cobitis taenia, a related but separate species from further west.
Morphology
Cobitis linea is a small, elongate loach, reported to reach only around 4 in in total length — modest even by the standards of this section of slender, sand-dwelling loaches. Like every member of the family Cobitidae it carries an erectile spine folded into a groove beneath each eye, which it can flick out defensively when threatened or handled; the skin around it is thin and the scales are tiny and deeply embedded, leaving the fish, in practical terms, close to scaleless.
As with other Cobitis species the body is built for a life spent close to the substrate: laterally compressed, with a small underslung mouth ringed by barbels for probing sand and mud, and a body pattern of dark blotches or a broken lateral line running along its flanks — features shared across the genus and used, along with fine details of the karyotype, to distinguish it from closely related spined loaches in the same drainage.
Habitat
This is a coldwater, temperate species, not a tropical one — Cobitis as a genus is confined to Europe and northern Asia and none of its members occur in warm, stable tropical rivers. Cobitis linea is known only as an endemic of the Kor River basin on Iran's Gulf coastal plain, where it inhabits muddy substrates in flowing water, a habitat typical for the genus: slow to moderate current over soft sediment that the fish can bury into or sift for food.
Because it is restricted to a single river basin, its entire known range is small, and like many Cobitis it likely experiences a genuinely seasonal climate with cold winters and warm summers rather than the constant warmth of a tropical stream. No detailed water-chemistry survey of the Kor River population appears in the available literature, so specific parameters beyond "cool, flowing, muddy-bottomed water" should be treated as provisional.
Feeding
No feeding study specific to Cobitis linea has been published, but the genus is a well-documented benthic sifter: related Cobitis species forage over soft substrate for small invertebrates — chironomid and other insect larvae, worms, tiny crustaceans — along with detritus, using barbels to locate food buried in mud or sand. Cobitis linea's muddy Kor River habitat is exactly the kind of substrate this feeding style depends on.
In the aquarium, Cobitis species in general take readily to live black mosquito larvae, frozen bloodworm, Tubifex and sinking tablets, and there is no reason to expect Cobitis linea to differ. A soft, sand or fine-mud substrate matters for this fish to forage and sift naturally, mirroring the muddy Kor River bottom it is adapted to.
Mating
Nothing specific has been published on courtship or pairing behaviour in Cobitis linea. FishBase notes only that the species is oviparous, possibly with distinct pairing during breeding — a pattern broadly consistent with other Cobitis, several of which show some pair or small-group courtship activity ahead of spawning rather than a purely chaotic mass release.
A karyological study of the Kor River population found a diploid chromosome number of 2n=50, with sex chromosomes that are cytologically indistinguishable — that is, males and females cannot be told apart from their chromosomes under the microscope, which is consistent with the general difficulty of sexing spined loaches by eye as well. Beyond these details, data on reproductive behaviour in this species is sparse.
Breeding
As a spined loach in the family Cobitidae, Cobitis linea is presumed to be an egg-scatterer that deposits adhesive eggs among plants or in the water column, typically in spring, with no parental care afterward — the pattern documented across the genus. Several temperate Cobitidae, including other Cobitis species and the dojo/weather loach Misgurnus, have been pond- or tank-spawned by hobbyists and researchers taking advantage of their tolerance for cool, seasonal water.
However, no spawning of Cobitis linea specifically — in the wild or in captivity — has been documented in the available literature. Given its narrow endemic range and the very limited published research on the species, the honest statement is that its breeding has not been observed and described; it should not be assumed to follow every detail of the pattern seen in better-studied relatives such as Cobitis taenia.
In the aquarium
Cobitis linea is essentially unknown in the aquarium hobby — it does not appear to be traded, and no common name has taken hold for it. Any care guidance has to be extrapolated from the genus: Cobitis are coldwater fish that do not need — and should not be kept in — a heated tropical setup. A soft sand or fine substrate is essential so the fish can bury and forage naturally, and as with all spined loaches its near-scaleless skin makes it sensitive to copper and full-strength medications, so any treatment should be approached cautiously and at reduced dose.
Given its very small known range in a single Iranian river basin and total absence from the trade, this is not a species a keeper is likely to encounter, and none of the trade pressures that affect farmed or wild-collected loaches elsewhere appear to apply here. Anyone who did acquire this fish should treat it as a temperate, unheated-tank species with a soft, sifting substrate rather than guess at tropical parameters.
Conservation
Cobitis linea has not been formally assessed on the IUCN Red List, so its conservation status is Not Evaluated — this is a statement of absent data, not a clean bill of health. Its known range is confined to the Kor River basin on Iran's Gulf coastal plain, and single-basin endemism of this kind is exactly the situation that tends to produce Data Deficient or threatened assessments once a species is formally reviewed, as has happened with a number of other narrow-range Cobitis and Sabanejewia in the Middle East and Anatolia.
No specific threats to Cobitis linea have been documented in the sources available here, and no trade pressure appears to exist since the species is not known in the aquarium trade. Its conservation picture should be read as simply unstudied rather than assumed safe, given how much regional freshwater habitat in Iran is under pressure from water extraction and damming.