Taxonomy & naming
Pethia sharmai was formally described by A. G. K. Menon and P. Rema Devi in 1993 in the Journal of the Bombay Natural History Society (vol. 89, no. 3, pp. 353–354). The type locality is Mogappair, West Annanagar, Madras (now Chennai), Tamil Nadu, India. The Catalog of Fishes (Eschmeyer, CAS) records the valid name as Pethia sharmai (Menon & Rema Devi, 1993), the parenthetical authority reflecting its transfer out of the originally assigned genus.
The original combination was Puntius sharmai; the genus Pethia was established by Pethiyagoda et al. in their 2012 revision of South Asian barbines, separating a cluster of small, deep-bodied Indian and Sri Lankan barbs from the old catch-all Puntius. The species is therefore sometimes referenced in older or popular literature as Puntius sharmai — both names refer to the same fish, but Pethia sharmai is the current valid combination under the Catalog of Fishes. The species epithet honours Bharat R. Sharma of the Indian Council of Agricultural Research.
Morphology
Pethia sharmai is a small, laterally compressed barb reaching a maximum of approximately 1–1.5 in standard length. Like other members of the genus it has a high-backed, deep body typical of the Indian small-barb guild. Colour details in the literature are sparse — the species has not been widely photographed in life — but the common name "sawfin barb" points to a serrated or notched dorsal fin ray, a feature shared by several Pethia species.
Sexual dimorphism follows the general pattern for the genus: males are likely slimmer with more saturated colouration, particularly during courtship, while females become noticeably fuller-bodied when gravid. Data on fin ray counts and lateral line scale counts come from the original description; the species has not been the subject of a detailed morphometric study beyond the type-series.
Habitat
Pethia sharmai is native to shallow, standing or slow-moving freshwater bodies in the Chennai metropolitan area — urban ponds and rain-fed lakes (locally called 'eries') that historically dotted the Tamil Nadu coastal plain. These waterbodies tend to be warm, relatively nutrient-rich and subject to seasonal fluctuation: full during the northeast monsoon and shrinking or drying in the hot season. FishBase lists the species as freshwater, benthopelagic and endemic to Tamil Nadu.
Water conditions recorded for the species by Seriously Fish span 68–79 °F, pH 5.5–7.5, and a hardness range of approximately 36–215 ppm — a relatively wide tolerance that reflects the variable chemistry of urban rain-fed tanks rather than the cool, oligotrophic streams inhabited by many other Indian barbs. The species is not recorded from rivers or hill-stream habitats.
Feeding
Pethia sharmai is a micropredator in the wild, foraging on small insects, crustaceans and zooplankton in the water column and at the surface film of its shallow-lake habitat. This diet is consistent with other small Pethia species of peninsular India, which exploit the invertebrate productivity of warm lentic systems.
In captivity the species is reported to accept a range of standard aquarium foods: live and frozen Daphnia and Artemia (brine shrimp), as well as quality flake and micro-pellet diets. A varied diet that includes small live or frozen invertebrates is likely to maintain good condition and colouration.
Mating
Like all barbs, Pethia sharmai is an egg-scattering, non-guarding spawner. There is no pair bond, no nest construction and no parental involvement beyond the act of spawning itself. During courtship a driving male pursues a gravid female through vegetation or over the shallow substrate, and the two fish press together briefly as eggs and milt are simultaneously released.
Colour and activity intensify in males at this time as they compete for access to ripe females. The adhesive eggs fall into vegetation or onto the substrate, where — left to the adults — they are readily eaten. No breeding in captivity has been formally documented in the aquarium literature for this species.
Breeding
Spawning in the wild presumably takes place among aquatic vegetation or fine substrate debris in the shallow lakes the species inhabits, with eggs scattered during the drive and left to develop unattended. Hatching and larval development would follow the general cyprinid pattern — eggs hatching within one to two days at tropical temperatures, with larvae becoming free-swimming a few days later once the yolk sac is absorbed.
No reliable account of captive breeding has been published. Given the species' rarity in the hobby and the precarious state of wild populations, captive propagation would be of genuine conservation value. A setup mirroring the shallow, warm, slightly acidic conditions of a Chennai eri — with fine-leaved plant cover or spawning mops and adults separated from eggs immediately after spawning — would be the logical starting point for anyone attempting it.
In the aquarium
Pethia sharmai is rarely available in the aquarium trade and is essentially unknown outside specialist circles interested in endemic Indian cyprinids. When kept, it is described as a very peaceful, timid and schooling species that does best in a group and should not be housed with boisterous or large tankmates that will outcompete it for food or stress it into hiding.
A species tank or a quiet community with other small, placid South Asian fishes is the most appropriate setting. Water should be soft to moderately hard (reflecting the variable chemistry of Chennai's urban lakes), with a temperature of 68–79 °F and a pH between 5.5 and 7.5. Planted cover is important for a fish that relies on vegetation for refuge and spawning substrate. Given its Endangered status, any captive specimens should be regarded as conservation assets rather than decorative stock.
Conservation
Pethia sharmai is assessed as Endangered (EN) on the IUCN Red List, with the evaluation carried out by N. Dahanukar in 2015. The primary driver is habitat destruction: the Chennai eries and urban ponds that constitute the species' entire known range are under severe pressure from the growth of one of India's largest cities. Urbanisation has reduced or degraded most of these waterbodies through infilling for development, extraction for irrigation and domestic use, and contamination by sewage and industrial runoff.
Compounding direct habitat loss is the spread of water hyacinth (Eichhornia crassipes), an invasive floating macrophyte that mats over the surface of warm, nutrient-enriched water bodies, reducing light penetration and oxygen levels and effectively smothering the aquatic communities beneath. FishBase lists the species as "scarce" in abundance. With such an extraordinarily small and fragmented range, any further reduction of Chennai's surviving urban wetlands poses an existential risk to this species.