Taxonomy & naming
Cobitis tetralineata was described in 1999 by Kim, Park & Nalbant in the Travaux du Musée National d'Histoire Naturelle "Grigore Antipa" (vol. 39, pp. 373–391), part of a wave of taxonomic work that split apart Korea's spined loaches, which had long been lumped under a small number of widespread Cobitis names. It remains in the genus Cobitis, the type genus of the family Cobitidae and the group from which the family and the whole superfamily Cobitoidea take their common name of "true loaches."
The species epithet tetralineata is straightforward Latin/Greek — tetra (four) plus lineata (striped) — describing the three to four dark-brown longitudinal stripes running along the mid-line of the body, the field mark used to separate it from its close relatives. It is often referred to in the ichthyological literature by its common name, the Korean sand loach, distinguishing it from the sympatric and phylogenetically close Cobitis lutheri with which it has since come into contact through human-mediated introduction.
Morphology
Cobitis tetralineata is a small, slender, laterally compressed loach typical of the genus, built low and elongate for life pressed against a sand bed. Like other members of the family Cobitidae it carries the erectile suborbital spine — a small, hinged spine folded into a groove beneath the eye that can be flicked out — and its skin is effectively naked, with tiny, deeply embedded scales rather than the overlapping scales of most fishes. That near-scaleless skin is the same feature that makes loaches broadly sensitive to copper and full-strength medications.
The defining field mark, and the source of its name, is a pattern of three to four dark-brown longitudinal stripes running along the flanks against a paler sandy ground colour — cryptic patterning well suited to a fish that spends most of its life lying on or buried in river sand. This is a temperate, coldwater species rather than a tropical one, and its build and colouring reflect a life spent hugging the bottom of a clear, flowing, sand-bedded river rather than cruising open water.
Habitat
This species is endemic to the Seomjin River system in South Korea, where it lives over clean sand substrates in flowing water — recorded current velocities of roughly 4–8 in/second and depths of about 12–59 in. It is a true sand-dweller, lying on or burrowing shallowly into the substrate rather than occupying rock or vegetation.
Cobitis tetralineata is markedly seasonal in its activity. It is active from March through October and spends the winter hibernating buried in the sand, emerging again as water temperatures rise in spring. This coldwater, temperate life cycle sets it apart from the tropical Cobitidae such as the horseface loach Acantopsis or the Lepidocephalichthys kuhlis, which experience no such winter dormancy — and it means this species is not a candidate for a heated tropical aquarium.
Feeding
As a sand-sifting benthic omnivore, Cobitis tetralineata forages by sifting through the sand for small invertebrates — chironomid (non-biting midge) larvae, testate amoebae of the family Arcellidae, and other small organisms living in and on the substrate. Field studies on the species report two peaks of feeding activity, in April and again in September, bracketing its active summer season.
This diet and foraging style is standard for the sand-loach guild: a soft, fine substrate is not decorative but functional, since it is what lets the fish sift and feed the way it does in the wild. In the aquarium this translates directly into a need for sinking, meaty foods — bloodworm, small worms and similar fare — offered over sand rather than gravel.
Mating
Detailed observations of courtship in Cobitis tetralineata are not well documented, but its reproductive biology follows the pattern established for temperate spined loaches: spawning is seasonal and cued by rising water temperature after the winter dormancy, rather than by any elaborate pairing behaviour. Field data point to a spawning season of roughly late June to mid-July at water temperatures around 72–79 °F, once the fish have emerged from winter hibernation and resumed active feeding.
As in other Cobitis, there is no evidence of parental care or nest-building — this is an egg-scattering species, and courtship is best understood as a brief, temperature-triggered event rather than a sustained pair bond.
Breeding
Cobitis tetralineata is a spined-loach egg-scatterer: ripe adults release adhesive eggs among plants or fine substrate in spring, with no parental care afterward. This is the well-documented pattern for the temperate Cobitidae — several coldwater species in this group, including other Cobitis, Sabanejewia, and the dojo or weather loach Misgurnus, have been pond- or tank-spawned by hobbyists and researchers, unlike the tropical Cobitidae (Acantopsis, Lepidocephalichthys), which generally have not.
For Cobitis tetralineata specifically there is no record of aquarium spawning in the sources available here; what is documented is the wild spawning window of roughly late June to mid-July at 72–79 °F, consistent with the broader temperate-Cobitis breeding calendar. Given how narrow its native range is and how little the aquarium trade handles it, this should be read as a species that is, at best, rarely bred outside its native river — not a fish with an established home-breeding record.
In the aquarium
Cobitis tetralineata is essentially unknown as an aquarium fish — it is a narrow-range Korean endemic studied mainly by field ecologists, not a species established in the hobby trade — so any care approach has to be extrapolated cautiously from its biology rather than from hobbyist experience. What the data do support is clear: this is a coldwater to cool-temperate species, not a tropical one, and it would need an unheated or lightly heated setup that tracks something closer to its native seasonal cycle, including a cooler winter period, rather than a steady tropical 79–82 °F.
Any tank for this species should mimic its sand-bed habitat closely: a soft, fine sand substrate deep enough to allow burrowing, moderate flow, and good oxygenation, with sinking foods offered to match its sifting feeding style. Like other Cobitidae it is near-scaleless and carries the erectile suborbital spine typical of the family, so the same caution about copper and full-strength medications that applies across true loaches applies here — dose gently and watch closely. Given the total absence of an established hobby track record, this is a species for the specialist prepared to research its native conditions rather than a fish to buy on impulse.
Conservation
Cobitis tetralineata has not been formally assessed on the IUCN Red List; it is treated here as Not Evaluated rather than assigned a guessed status. It is a narrow-range endemic, known only from the Seomjin River system in South Korea, which is the kind of restricted distribution that often correlates with vulnerability even absent a formal assessment.
The clearest documented conservation concern for this species is not habitat loss but human-mediated introduction: genomic research has shown that Cobitis tetralineata has been artificially introduced from its native Seomjin River into the neighbouring Dongjin River, where it now hybridizes with the native Cobitis lutheri. That hybridization is driving genomic replacement of the native population — a case where the loach's own spread, not overcollection, is the documented threat, and a reminder that moving even native regional fish between river systems can quietly erode a distinct species' genetic identity.