Taxonomy & naming
The species was described by A. G. K. Menon in 1984 as Mesonoemacheilus petrubanarescui, honouring the Romanian ichthyologist Petre Mihai Bănărescu, a major contributor to the study of Old World freshwater fish taxonomy including the nemacheilid loaches. Like many South and Southeast Asian stone loaches described in the twentieth century under the broad genus Nemacheilus (and its near-synonym Noemacheilus), it has since been moved as the family was repeatedly revised on the basis of osteology and later molecular work. The Catalog of Fishes, the authority for valid names, currently places this species in Mesonoemacheilus, as Mesonoemacheilus petrubanarescui.
This article keeps the original combination, Mesonoemacheilus petrubanarescui, in line with the site's working slug for this species, but readers researching it further should expect to find the bulk of modern literature, including its FishBase and IUCN entries, filed under Mesonoemacheilus petrubanarescui. It belongs to the family Nemacheilidae, the stone or brook loaches, the largest family of loaches, and to the small hillstream genus Mesonoemacheilus which is largely restricted to peninsular India.
This fish was long listed as Nemacheilus petrubanarescui; Eschmeyer's Catalog of Fishes places the species in Mesonoemacheilus, and the current combination Mesonoemacheilus petrubanarescui is followed here.
Morphology
This is a small, slender loach: FishBase gives a maximum length of only about 1.4 in standard length, making it one of the smallest species in the loach atlas. Like other nemacheilids it has a cylindrical, elongate body, a small subterminal mouth suited to picking food off stones, and barbels around the mouth for feeling out prey in the streambed. The skin carries the family's characteristic near-scaleless texture, and where a suborbital spine is present in related genera it is far less developed than in the botiid loaches — this is a soft-bodied, camouflaged fish built for clinging to pebbles in current, not for defence.
Detailed morphological description beyond the original taxonomic literature is sparse; no aquarium-hobby photography or measurement record beyond the type material and FishBase summary is available in the sources consulted here, so specifics of colour pattern and fin proportions are not confidently reported.
Habitat
Mesonoemacheilus petrubanarescui is endemic to the Western Ghats of southern India, known only from the Netravati and Kabani river systems spanning Karnataka and Kerala. It lives in pebbly, rocky-bottomed streams — the classic hillstream habitat of clear, fast-flowing, well-oxygenated water running over stone and gravel rather than sand or silt.
The IUCN assessment lists it from only two known locations, and its range appears to be genuinely narrow rather than simply under-recorded. This kind of single- or few-stream endemism is common among the smaller nemacheilids of the Western Ghats, many of which are found nowhere else on Earth.
Feeding
As a small nemacheilid loach of fast, clear streams, Mesonoemacheilus petrubanarescui is best understood as a benthic micro-predator, picking small invertebrates — aquatic insect larvae and tiny crustaceans — from among the stones of its home rivers, in keeping with the feeding ecology described for its close relatives in the genus Mesonoemacheilus. Seriously Fish's profile for the species (filed under its current name) lists small live and frozen foods such as Daphnia, Artemia and bloodworm as appropriate aquarium fare, alongside high-quality sinking dried foods; it is not reported to take flake reliably.
No species-specific feeding study has been published for this fish, so the diet notes here follow the pattern documented for the genus and family rather than direct observation of M. petrubanarescui itself.
Mating
Nothing specific has been documented about courtship or spawning behaviour in Mesonoemacheilus petrubanarescui. Seriously Fish states plainly that breeding is undocumented, both in the aquarium and in the wild. Stone and brook loaches in general are egg-scatterers with no pair bond or parental care, and there is no reason to expect this species departs from that pattern, but no direct observation of ripening, courtship or spawning has been recorded for it.
Breeding
This species has not been bred in the aquarium, and no wild spawning has been documented either — the sources consulted here describe breeding as simply undocumented. Based on what is known of Nemacheilidae generally, the expected mode is an egg-scatterer laying over gravel or among stones in flowing water with no parental care, but this is inference from the family rather than a confirmed observation for M. petrubanarescui.
Given its Endangered status, its restriction to two known river systems, and the complete absence of a breeding record, this is a species where captive-breeding knowledge would be genuinely valuable for conservation — but as things stand, keepers should not expect to reproduce it, and any successful spawning would be worth documenting carefully.
In the aquarium
Mesonoemacheilus petrubanarescui is essentially unknown in the aquarium trade and is not a species most keepers will encounter for sale. Where care information exists, drawn from Seriously Fish, it calls for a tank of at least 60×11.8 in with strong water movement — a powerhead or airstone-driven current is recommended to simulate the fast hillstream flow this fish evolved in — over a substrate of rocks, sand, fine gravel and boulders that lets it wedge into the current the way it would among the pebbles of the Netravati and Kabani. Water chemistry sits in a moderate range, roughly 64–78 °F and pH 6.0–7.5 with soft-to-moderately-hard water (36–215 ppm), noticeably cooler than the warm, still conditions many aquarists default to for tropical fish.
It is described as a peaceful, group-living species, with a recommendation of four or more kept together. As with other near-scaleless loaches, caution with copper-based and full-strength medications is prudent even though this is not explicitly stated for the species; the family as a whole is medication-sensitive. Regular partial water changes (30–50% weekly) are advised to keep the strong, clean-water conditions this stream-dwelling fish needs. Given its conservation status and the total absence of any established aquarium supply chain, this is not a species to seek out from the wild.
Conservation
Mesonoemacheilus petrubanarescui is assessed as Endangered (EN) on the IUCN Red List. The assessment records it as known from only two locations — the Netravati and Kabani river systems — and cites habitat alteration, sand mining and pollution as the threats driving its restricted, precarious status. FishBase similarly reports it as endemic to these two Western Ghats river systems.
As a narrow-range stream endemic with no significant aquarium trade to draw on it, its conservation outlook depends entirely on the health of its home rivers in Karnataka and Kerala. Sand mining and pollution pressures on Western Ghats streams are a recurring threat across many small endemic fish in the region, and this species' confinement to just two known locations leaves it with very little buffer against further habitat loss.