Taxonomy & naming
Acanthocobitis pavonacea was described by the Scottish naturalist John McClelland in 1839, originally as Cobitis pavonacea. Like many Asian stream loaches it passed through the old catch-all genus Noemacheilus (as Noemacheilus pavonaceus) before the modern classification of the family Nemacheilidae settled it into Acanthocobitis. The Catalog of Fishes recognizes Acanthocobitis pavonacea as the valid combination and treats it as the type species of the genus, with Acanthocobitis longipinnis as the only other currently recognized member.
The genus name combines the Greek akantha (spine) with a nod to the family's loach relatives, referencing the erectile suborbital spine characteristic of the group. The family Nemacheilidae — the stone and brook loaches — is the largest of the loach families, and much of its internal taxonomy has been repeatedly revised as older Nemacheilus- and Noemacheilus-type names were split across many newer genera; a fish labeled with one of those older names in older literature or the trade is very likely this same species.
Morphology
Acanthocobitis pavonacea is a slender, elongate stone loach reaching roughly 5–6 in in standard length — a respectable size for a nemacheilid, larger than many of its smaller stream-loach relatives. As in other members of the family it carries the small, erectile suborbital spine typical of loaches, and its skin is effectively naked to the touch, with tiny, deeply embedded scales rather than the more obvious scaling of many other freshwater fish groups.
Detailed pattern and fin-shape descriptions were not available in the sources consulted for this profile; the common names "spearfin" and "peacock" loach point to a patterned, likely barred or mottled body and pointed fin structure typical of the genus, but specific colouration data is data-sparse and not asserted here beyond what the cache confirms.
Habitat
This species is native to the Brahmaputra and Ganges river basins of northern India and Bangladesh, where it inhabits cool, moving stream and river water. Water chemistry reported for the species is a pH of roughly 6.0 to 7.5 with a temperature range of about 64–77 °F — meaningfully cooler than the warm tropical water many aquarium fish are kept in, and consistent with the fast, oxygen-rich streams typical of Nemacheilidae habitat across the Himalayan foothills and northern Indian subcontinent.
As a benthic stream dweller it is adapted to hold position against current on the streambed, and it is described as a peaceful bottom dweller that appreciates the company of its own kind. Strong water movement and good oxygenation are core habitat requirements, not optional extras.
Feeding
As with most Nemacheilidae, Acanthocobitis pavonacea is a bottom-foraging micro-predator, working the substrate of fast, clear streams for small invertebrates such as insect larvae and tiny crustaceans. Specific dietary data for this species was not found in the sources consulted, but related Acanthocobitis and other stone loaches show a consistent preference for this feeding style.
In the aquarium, sinking foods that reach the bottom — small live and frozen fare such as bloodworm and brine shrimp alongside sinking pellets — are the most reliable way to feed a fish adapted to picking prey items directly off gravel and stone rather than taking food from mid-water or the surface; flake is easily missed by a fish that rarely leaves the bottom.
Mating
No specific courtship or spawning behaviour for Acanthocobitis pavonacea was found in the sources consulted for this profile. Stone and brook loaches in general show little documented reproductive behaviour in the aquarium literature, since most Nemacheilidae are rarely kept under conditions that trigger spawning and are not commercially propagated the way larger ornamental loach groups are.
What can be said with confidence, drawing on the wider pattern for this family, is that reproduction in the wild is expected to follow the group's typical model: eggs are released over the substrate in flowing water rather than deposited in a nest or guarded site, with no evidence of pair formation or parental investment beyond spawning itself.
Breeding
Acanthocobitis pavonacea is not known to be regularly bred in home aquaria, and no verified spawning accounts were found in the sources consulted. Consistent with the wider pattern for stone and brook loaches (Nemacheilidae), the expected mode is egg-scattering over gravel and among stones in fast-flowing water, with no parental care of eggs or fry.
This is an honest gap rather than an oversight: most Nemacheilidae species are narrow-range stream endemics that see little aquarium interest and correspondingly little breeding literature. Anyone keeping this species should expect to enjoy it as a hardy, long-lived stream fish rather than pursue captive breeding, for which essentially no established protocol exists.
In the aquarium
Acanthocobitis pavonacea calls for a streamlined setup built around its native cool, fast-flowing habitat rather than a typical warm community tank: a temperature of about 64–77 °F, pH near 6.0 to 7.5, and strong water movement with high oxygenation are the essentials. A sand or fine-gravel substrate with boulders and driftwood to break current and provide grazing surfaces suits the fish well, and — as with related Acanthocobitis species — filtration turning over several times the tank volume per hour helps recreate the flow of a natural stream.
Being a scaleless-skinned loach, it shares the family's sensitivity to copper and to full-strength medications, so treatments should be dosed cautiously. It is described as a peaceful bottom dweller that appreciates the company of its own kind, so keeping a small group rather than a lone individual is the more considerate approach, even though the strict obligate-shoaling behaviour documented in some botiid loaches has not specifically been reported for this species. Tankmates should be other cool-water- or unstressed-by-current species, since a warm, still community tank is the wrong environment for this fish.
Conservation
Acanthocobitis pavonacea has not been evaluated by the IUCN Red List and carries no assigned conservation category; this is typical for many narrow-range stream loaches across South Asia that have simply never been assessed, rather than evidence that the species is secure. No population trend or threat data was found in the sources consulted for this profile.
As a stream-dwelling species of the heavily populated and intensively used Brahmaputra and Ganges basins, it likely faces the same generic regional pressures common to South Asian freshwater fish — water abstraction, pollution and habitat alteration — though no species-specific documentation of these pressures was located, and none is asserted here beyond that general caution.