Taxonomy & naming
Cobitis macrostigma was described by the French naturalist Pierre-Marie-Alphonse Dabry de Thiersant in 1872. It has always sat in the genus Cobitis, the type genus of the family Cobitidae and the group after which the whole "spined loach" family is named, and the Catalog of Fishes continues to list it under this combination.
A 2023 study sequencing its complete mitochondrial genome (16,573 base pairs, 13 protein-coding genes, 22 tRNAs and 2 rRNAs) placed it phylogenetically close to Cobitis qujiangensis within the subfamily Cobitinae, consistent with its Yangtze-basin distribution and its membership in the diverse East Asian radiation of the genus. The species has not been evaluated by the IUCN Red List, so no conservation status has been assigned.
Morphology
Cobitis macrostigma is a slim, elongate loach typical of the genus: a rounded, only mildly compressed body, a pointed snout with barbels for probing the substrate, and small eyes set high on the head. Beneath each eye it carries the erectile, forked suborbital spine that is diagnostic of the family Cobitidae — a defensive structure the fish can flick out when handled or threatened, and one reason loaches should be moved with care rather than squeezed in a net.
The species is reported to reach a maximum of about 5.5 in standard length, with 4.5 in a more typical adult size; females grow noticeably larger than males, a common pattern in Cobitis. Like other true loaches its scales are tiny and deeply embedded, leaving the skin functionally naked — a trait that matters for disease susceptibility and medication dosing rather than for outward appearance, since the body still shows the mottled, blotchy patterning typical of the genus.
Habitat
This species is endemic to the middle and lower reaches of the Yangtze River in China, a large subtropical river system rather than a small headwater stream. It is a benthopelagic freshwater fish, living close to the bottom in still to slow-flowing water over soft sand and silt substrates where it can bury and forage.
Water temperatures across its range run from roughly 50–75 °F, spanning cool winters and warm subtropical summers — this is a coldwater-to-temperate loach, not a heated tropical species, and it does not need — or want — a permanently warm aquarium. In the home tank it should be kept in unheated to lightly warmed, well-oxygenated water over a fine, soft substrate that lets it exhibit its natural sand-sifting behaviour.
Feeding
Cobitis macrostigma is a benthic omnivore with a trophic level (around 3.3 on FishBase) that reflects a diet weighted toward small invertebrates with some plant and detrital material mixed in. In the wild it forages by sifting soft sand and silt, taking worms, insect larvae, small crustaceans and other invertebrates it roots out of the substrate.
In the aquarium it feeds readily on standard foods — sinking pellets, wafers, and frozen or live foods such as bloodworm and small crustaceans — and adapts well to prepared diets. As with all sand-sifting loaches, a soft, fine substrate is important so the fish can express its natural foraging behaviour rather than abrading itself on coarse gravel.
Mating
FishBase notes that Cobitis macrostigma shows distinct pairing during breeding, a trait recorded for a number of Cobitis species in which males and females associate closely around spawning rather than spawning in a diffuse group. Detailed accounts of courtship behaviour for this particular species are not available in the sources consulted here, and data on external sexual dimorphism beyond the larger size of females is sparse.
As a temperate-to-subtropical member of the genus, spawning in the wild is likely tied to seasonal warming in spring, the pattern documented for related Cobitis and for the dojo loach Misgurnus, though this has not been specifically confirmed for macrostigma in the sources available.
Breeding
Cobitis macrostigma is oviparous, scattering eggs rather than guarding a nest or brooding young — loaches in general are egg-scatterers with no parental care, and nothing in the available sources suggests this species is an exception. Several temperate Cobitis species, along with the dojo/weather loach Misgurnus, have been pond- or tank-spawned by hobbyists and breeders taking advantage of their coldwater tolerance and a seasonal temperature cue, in contrast to tropical Cobitidae such as the horseface loach Acantopsis, which are rarely if ever bred at home.
For Cobitis macrostigma specifically, no confirmed reports of captive breeding were found in the sources consulted. Given its close relationship to other temperate, unheated-tank-tolerant spined loaches, tank or pond spawning may well be achievable with a seasonal cool-to-warm cycle, but this should be treated as plausible rather than demonstrated — the honest picture is that this species, like most loaches, is essentially not bred in home aquaria at present.
In the aquarium
This is a peaceful, undemanding bottom-dweller well suited to an unheated or lightly heated community aquarium, given its natural tolerance of 50–75 °F water. It should be given a soft, fine sand or silt substrate for sifting and burrowing, since a coarse or sharp substrate can injure its barbels and sensitive underside, and it appreciates some cover such as smooth rockwork or driftwood to retreat into.
As with all true loaches, its near-scaleless skin makes it sensitive to copper-based medications and full-strength treatments generally; half-doses and gentle products are the safer approach if disease treatment becomes necessary. Being a peaceful, non-aggressive species, it does well alongside other calm coldwater or subtropical fishes rather than boisterous tankmates, and — as for most loaches — keeping it in a small group rather than singly is likely to suit its natural, gregarious bottom-dwelling habits, even though group-specific behaviour has not been documented for this species.
Conservation
Cobitis macrostigma has not been formally assessed by the IUCN Red List and carries a status of Not Evaluated. No population trend, threat assessment or conservation action has been published for this species in the sources consulted.
As a river endemic restricted to the middle and lower Yangtze — one of the most heavily modified and intensively used river systems in the world, subject to damming, pollution and habitat alteration — it is reasonable to expect the species faces some of the same pressures documented for other Yangtze basin fishes, but without a formal assessment this remains an inference rather than a documented finding. There is no evidence in the available sources of significant aquarium-trade collection pressure on this species.