Taxonomy & naming
Misgurnus nikolskyi was described by the Russian ichthyologist E. D. Vasil'eva in 2001, one of several pond-loach species split out from the historically broad and confused Misgurnus fossilis / M. anguillicaudatus species complex as researchers worked out the true diversity of Eurasian weather loaches. It belongs to the family Cobitidae, the true spined loaches, and sits in the genus Misgurnus alongside the European weather loach (M. fossilis) and the widely-traded dojo or Oriental weather loach (M. anguillicaudatus).
The species epithet honours the Russian zoologist Aleksandr Mikhailovich Nikolskii. As with much of the Misgurnus complex, older literature and databases sometimes lump Amur-basin pond loaches under M. anguillicaudatus or M. mohoity; the Catalog of Fishes is the authority for the currently valid combination, and this article keeps the genus as Misgurnus per that standard rather than attempting any reassignment.
Morphology
Like other members of its genus, Misgurnus nikolskyi is an elongate, eel-like loach with a rounded body, a small head, and the barbels typical of pond loaches clustered around the mouth. FishBase reports males reaching about 5.5 in total length and females somewhat larger at up to about 6 in — a modest size for the genus. The skin is embedded with tiny, deeply sunk scales that leave the fish effectively naked to the touch, the same near-scaleless condition seen across the family and the reason Cobitidae are so sensitive to medication.
As a true loach it carries the family's diagnostic erectile suborbital spine, a small defensive spine folded into a groove beneath the eye that can be flicked out when the fish is handled or threatened. Misgurnus species are also notable facultative air-breathers: alongside gill respiration they can gulp air at the surface and absorb oxygen through the hindgut, an adaptation that lets them survive in poorly oxygenated, weedy or even stagnant water — the trait that gives the group its "weather loach" name, since restless surfacing behaviour was once read as a sign of changing barometric pressure.
Habitat
The species was described from and is native to the Amur River drainage of Far East Russia, a large temperate river system with cold winters and warm summers. It is a bottom-dwelling fish of slow-flowing rivers, backwaters, oxbows and vegetated shallows, burrowing into soft sand or silt substrate for much of the day and emerging to forage, much as its dojo relative does across East Asia.
This is unambiguously a coldwater, temperate species, not a tropical one. Research published in the Journal of Ichthyology and in Springer Nature documents that M. nikolskyi has expanded well beyond its native Amur basin, having been recorded establishing itself in the Ob River basin and the Balkhash–Ili basin of Kazakhstan in Western Siberia — a naturalized range extension likely aided by its tolerance of a wide temperature span and its resilience as a burrowing, air-breathing survivor.
Feeding
Misgurnus nikolskyi is a sand-sifting benthic omnivore. FishBase places it at a trophic level of about 3.2, consistent with a secondary consumer that forages through soft substrate for aquatic insect larvae, worms, small crustaceans and other invertebrates, along with organic detritus stirred up from the bottom. Its barbels and mobile, downturned mouth are built for probing sand and silt rather than picking at the water column.
In captivity a fish of this type would be expected to take the same varied bottom-feeding diet as the dojo loach — sinking pellets and wafers, frozen bloodworm and blackworm, and other meaty foods offered near or on a soft substrate it can work through. A bare or coarse-gravel bottom denies it the natural sifting behaviour central to how it feeds.
Mating
Specific breeding behaviour for Misgurnus nikolskyi is not documented in the sources consulted, so this section draws on the well-established pattern for the genus rather than species-specific observation. Sexing Misgurnus loaches in general relies on subtle cues — females tend to run deeper-bodied when gravid, and males of some congeners develop a slightly thickened second pectoral-fin ray — but overt external dimorphism is limited.
As a temperate pond loach, its reproduction would be expected to follow the seasonal pattern typical of the genus: spawning triggered by rising water temperature and day length in spring, with ripe fish moving into shallow, weedy margins to release and fertilize eggs among vegetation, rather than the flood-migration spawning seen in tropical botiid loaches.
Breeding
No aquarium or hatchery spawning records for Misgurnus nikolskyi specifically were found in the sources consulted. Based on the documented biology of the genus, spined and pond loaches like Misgurnus scatter adhesive eggs among plants, typically in spring, with no parental care given afterward. Several temperate species in this family — including the European weather loach (Cobitis and Sabanejewia relatives) and, most relevantly, the dojo or weather loach (Misgurnus anguillicaudatus) — have been successfully pond- or tank-spawned by hobbyists and breeders, in clear contrast to tropical Cobitidae such as the horseface loach (Acantopsis) or Lepidocephalichthys, which generally have not.
Given that M. nikolskyi is a close, cold-adapted relative of the dojo within the same genus, a similar egg-scattering, plant-associated spawning strategy without parental care is the reasonable expectation, set out here as inference from genus biology rather than a confirmed record for this species.
In the aquarium
Misgurnus nikolskyi is essentially unknown in the aquarium trade and has no established hobby history; this section is included for completeness rather than as a care guide the way it would be for a commonly kept species. What can be said with confidence, based on the genus and the practical-fishkeeping literature on Misgurnus water requirements, is that this is a coldwater fish: the genus is documented as tolerant of roughly 36–86 °F with a comfortable range around 41–77 °F, and it should never be treated as a tropical species requiring a heater. It would want a soft sand substrate to burrow and sift through, since denying a Misgurnus loach the ability to dig is one of the more common keeper mistakes with this genus.
As with all Cobitidae, its near-scaleless skin means it would be sensitive to copper-based medications and to full-strength treatments generally, calling for reduced dosing and caution if disease treatment is ever needed. Its facultative air-breathing also means it tolerates lower dissolved oxygen than most fish, but that is a survival adaptation, not a reason to neglect filtration and water quality.
Conservation
FishBase lists Misgurnus nikolskyi as Least Concern on the IUCN Red List, assessed in 2020, with medium resilience and low vulnerability to fishing pressure. This reflects a species that remains widespread within its native Amur basin range and has additionally proved able to establish itself outside that range, having been recorded expanding into the Ob River basin and the Balkhash–Ili basin of Kazakhstan in Western Siberia.
That range expansion is itself a conservation-relevant point: research in the Journal of Ichthyology and Springer Nature documents M. nikolskyi as a naturalizing, non-native colonizer in parts of Western Siberia, raising ecological questions for those invaded systems even as the species' own native-range status remains secure. There is no evidence in the sources consulted of aquarium-trade collection pressure on this species.