Taxonomy & naming
Pethia manipurensis was described by A. G. Kottelat Menon and K. S. Devi in 2000, with the type locality recorded as Lake Loktak, Moirang, Manipur, India. The original description placed the fish in the genus Puntius, the large catch-all assemblage that long held most South and Southeast Asian small barbs, giving the original combination Puntius manipurensis Menon & Devi, 2000.
Following Pethiyagoda et al. (2012), the majority of South Asian small barbs — including the species of peninsular India and the northeast — were redistributed across several resurrected or newly erected genera. Pethia was established for a cluster of Indian subcontinent barbs, and P. manipurensis was transferred to this genus under the current valid combination. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name, and the parenthetical around the author pair indicates the genus move. FishBase records the species as benthopelagic and tropical freshwater, confined to the Brahmaputra basin drainage that encompasses Loktak Lake. No subspecies or geographic variants have been described.
Morphology
Pethia manipurensis is a small barb, reaching a maximum standard length of approximately 2.5 in per FishBase records. Like other members of the genus Pethia it has the compact, somewhat deep-bodied and laterally compressed form typical of small South Asian barbs, with a relatively blunt snout and the small, terminally positioned mouth suited to picking food items from the substrate and water column.
Detailed colour descriptions from the original description and hobbyist accounts note the typical barb pattern of a pale silvery to straw-coloured body with darker markings, though exhaustive colour notes from the wild are limited given the species' restricted range and low abundance. Sexual dimorphism follows the barb pattern common to the genus — females become noticeably fuller in the abdomen when gravid, while males tend toward a slimmer profile.
Habitat
The species is endemic to Loktak Lake, situated at roughly 793 metres elevation in the Bishnupur and Imphal West districts of Manipur, northeastern India. Loktak is the largest natural freshwater lake in northeast India and the largest in the country outside the Himalayan region, draining into the Manipur River and ultimately the Brahmaputra system. The lake is notable for its phumdis — thick, floating heterogeneous masses of soil, vegetation and organic matter — which provide shelter, foraging ground, and spawning habitat for a number of endemic and near-endemic fishes including P. manipurensis.
Water conditions recorded from the lake and referenced by Seriously Fish for the species include temperatures in the range of 64–77 °F and a pH of 5.5–7.5 (soft to slightly acidic to neutral), with hardness ranging from 36 to 268 ppm. The fish appears to prefer cooler conditions within this range, consistent with the lake's elevated position. Since the closure of the Ithai Barrage on the Manipur River in 1983, the hydrological balance of the lake has been substantially altered, with raised mean water levels, accelerated phumdi formation in some areas, and worsened water quality across much of the basin.
Feeding
In the wild, Pethia manipurensis is an opportunistic omnivore foraging across the substrate and water column, taking diatoms, filamentous algae, detritus, small insects, worms, crustaceans, and zooplankton — a diet typical of small benthic and benthopelagic barbs in lentic or slow-water habitats. The floating phumdi mats and the lake margins offer a diverse array of fine organic matter, invertebrates, and algal growth that the species exploits.
In aquarium conditions the species accepts a wide range of foods. Seriously Fish recommends a diet of live and frozen foods such as bloodworm, Daphnia, and Artemia alongside quality dry foods (flakes and small granules). Providing plant-based components alongside protein-rich items reflects the mixed natural diet and supports condition in captive fish.
Mating
Pethia manipurensis is an egg-scattering, non-guarding spawner, consistent with the reproductive strategy of the genus Pethia and of barbs generally. No pair bond is formed, no nest is constructed, and no territory is held beyond a brief period of courtship activity. A reproductively ready male pursues a gravid female through fine-leaved vegetation, over substrate, or among the organic matter of the phumdi margins, the two coming briefly together to release eggs and milt simultaneously.
Courtship colour may intensify in males competing for access to gravid females. After spawning there is no further investment in the eggs or any resulting fry by either parent — the scattered, adhesive eggs are left where they fall, and the adults will readily consume them if they encounter them.
Breeding
Breeding in aquaria follows the standard barb protocol. Seriously Fish notes that P. manipurensis is a free-spawning egg-scatterer with no parental care. A conditioning period on varied live and frozen foods will bring a small group or selected pair into spawning condition, after which spawning is typically triggered in a mature, dimly lit aquarium with fine-leaved plants or spawning mops and, ideally, a substrate arrangement — mesh, marbles, or deep fine gravel — that protects eggs from the adults.
Eggs are adhesive and should be left to develop in the absence of the spawning adults, which are removed promptly after spawning concludes. Though detailed hobbyist breeding accounts are limited given the species' relative rarity in the trade, it has been bred commercially to some extent, which provides at least a partial buffer against the demand for wild-caught fish. Incubation and larval development timescales are not well documented in published sources accessible to this account.
In the aquarium
Pethia manipurensis is an uncommon but not unknown aquarium fish, available occasionally through specialist suppliers and bred commercially in limited numbers. Seriously Fish classifies it as a peaceful schooling species that should be kept in groups of at least 6–10 individuals, where its social behaviour is properly expressed and individual fish are less prone to stress. It is suited to a community of similarly sized, non-aggressive fishes.
The species' cool-water preference — 64–77 °F, favouring the upper end of that range — and its moderately acidic to neutral water requirements (pH 5.5–7.5, soft to moderately hard) make it a reasonable choice for unheated or lightly heated aquaria in temperate climates. A mature, well-filtered tank with subdued lighting, some fine-leaved planting, and open mid-water swimming space echoes the structure of its phumdi-fringed lake habitat. Diet is straightforward — the species accepts live, frozen, and quality dry foods readily. Given the pressures on its wild population, sourcing captive-bred specimens is strongly preferred.
Conservation
Pethia manipurensis is assessed as Endangered (EN) on the IUCN Red List, with the assessment attributed to Singh (2015) via GBIF records. The species' entire known range is confined to Loktak Lake, making it acutely vulnerable to any degradation of that single ecosystem. Multiple converging threats have placed the lake under severe pressure: eutrophication driven by agricultural runoff from surrounding farmland, siltation from catchment erosion, untreated domestic and industrial effluent, and over-exploitation of the lake's fisheries resources.
The 1983 completion of the Ithai Barrage on the Manipur River fundamentally altered the lake's hydrology, raising mean water levels and disrupting the seasonal water-level fluctuations that govern the ecology of the phumdis and the fishes that depend on them. Seriously Fish notes that wild populations are declining and the species is not considered abundant in its natural habitat. Commercial breeding provides some supply to the aquarium trade and reduces collection pressure, but does not address the lake-level threats to the wild population. Loktak Lake is designated a Ramsar Wetland of International Importance and the surrounding area includes the Keibul Lamjao National Park, but enforcement of protections remains imperfect and water quality continues to decline in parts of the lake.