Taxonomy & naming
Pethia guganio was described by Francis Hamilton in 1822 from the rivers of the Bengal region, where it was known by the local vernacular name that gave the species its epithet. Hamilton's original placement was in the genus Cyprinus in the broad pre-Linnaean sense; the species was subsequently moved through the old aggregate genera Barbus and Systomus before landing for most of the twentieth century in the catch-all Puntius, where it was widely known as Puntius guganio.
The current valid combination, Pethia guganio, reflects the 2012 revision by Pethiyagoda, Meegaskumbura and Maduwage, who erected the genus Pethia to accommodate a group of small, spotted and banded barbs distributed across the Indian subcontinent and Sri Lanka. The parenthetical authority — (Hamilton, 1822) — marks the transfer out of Hamilton's original genus. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name. Older aquarium literature and some trade sources still use the name Puntius guganio; the Seriously Fish profile for the species retains that former combination.
Morphology
Pethia guganio is a moderately elongate, laterally compressed barb reaching a maximum total length of about 3 in, making it one of the larger Pethia species. The body form is typical of the genus: a fairly high-backed profile, a blunt snout, and a small, sub-terminal mouth suited to picking invertebrates and fine food items from the substrate and water column.
The coloration is silvery to pale golden, with a translucent quality that partly earns the common name glass barb. Sexual dimorphism is moderate; females become visibly plumper and rounder in the abdominal region when gravid, a trait shared with most other Pethia species. Detailed colour and lateral-line scale counts are recorded in Hamilton's original description and subsequent systematic treatments.
Habitat
Pethia guganio is a fish of lowland freshwater habitats across the Indo-Gangetic plain. It inhabits slow-moving and standing waters — pools, beels, canals, ditches, ponds and the backwater margins of larger rivers — typically over sandy substrate. It also enters the quieter reaches of rivers and may use adjacent floodplain wetlands during the monsoon season.
The species is found in the Ganges and Brahmaputra drainage systems in northern and northeastern India (Uttar Pradesh, Bihar, West Bengal, Assam, Orissa) and across Bangladesh, with the IUCN recording an extent of occurrence of approximately 120,0 mi². The water it inhabits is broadly tropical to subtropical in temperature and near-neutral in reaction, consistent with the warm, often turbid lowland rivers of the subcontinent.
Feeding
Pethia guganio is a micropredator in the wild. Seriously Fish characterises it as feeding on small insects, worms, crustaceans and zooplankton, supplemented by fine organic matter — the typical diet of a small, active benthopelagic barb that forages across the substrate and lower water column in slow to still waters.
In the aquarium the species accepts small dried foods but responds best to a varied diet with a strong live and frozen component: Daphnia and brine shrimp are particularly recommended. The bent toward small live prey reflects its natural foraging ecology in the rich, invertebrate-laden shallows of the Bengali floodplain.
Mating
Like all barbs, Pethia guganio is an egg-scattering, non-guarding spawner. There is no nest, no pair bond beyond the spawning act, and no parental investment after eggs are released. A driving male pursues a gravid female through vegetation or over the sandy substrate, and the two briefly press together as eggs and milt are shed into the water column or onto plants and bottom material.
The adhesive eggs sink and adhere where they land. Adults pay no attention to the spawn once released; in the presence of the parents, eggs and subsequent fry are at significant risk of predation. Courtship activity is likely tied to seasonal cues — temperature, water level and food availability — in the monsoonal lowland rivers the species inhabits.
Breeding
Aquarium breeding of Pethia guganio has not been formally documented in the hobby literature reviewed, and Seriously Fish notes it as unrecorded in captivity. Following the biology of closely related Pethia species, it is expected to spawn in the manner typical of the genus: eggs are scattered among fine-leaved plants or over the substrate, hatch within one to two days at tropical temperatures, and the larvae become free-swimming after a further few days.
Hobbyists wishing to attempt breeding would likely follow protocols used for similar small Pethia species: a separate, shallow spawning tank with soft-to-moderate water, a temperature toward the upper end of the tolerance range, fine-leaved planting or spawning mops, and removal of the adults immediately after spawning. First foods for larvae would be infusoria followed by newly hatched brine shrimp. The species' apparent scarcity in the trade means that documented captive spawnings remain sparse.
In the aquarium
Pethia guganio is uncommon in the aquarium hobby. Seriously Fish notes it as a poorly known species in trade, and it lacks the wide availability of more popular Indian barbs such as Pethia conchonius or Pethia ticto. When kept, its requirements follow those of lowland South Asian barbs: a spacious tank with moderate to gentle flow, a sandy or fine gravel substrate, open swimming space alongside some planting, and water in the approximate range of 64–79 °F with a pH of 6.0–7.5.
It is described as a peaceful species, best kept in a shoal of eight to ten individuals, which moderates inter-fish competition and encourages natural schooling behaviour. Suitable tankmates are other peaceful, similarly sized South Asian species. Small live and frozen foods are important for long-term condition. The obscurity of this barb in the trade means sourcing may require specialist importers.
Conservation
Pethia guganio is listed as Least Concern (LC) on the IUCN Red List, assessed on 20 March 2010 and published in 2015 (assessor N. Dahanukar, taxon ID 166607). The justification cites the species' wide distribution across the Ganges and Brahmaputra drainages of Bangladesh and northeastern India, with an estimated extent of occurrence of around 120,0 mi², and the absence of identified major range-wide threats at the time of assessment.
The IUCN annotation acknowledges that the assessment needs updating — a reflection of how much the picture of lowland river health in South Asia has changed since 2010. The principal pressures on the species' habitat are those affecting Indo-Gangetic wetlands broadly: agricultural water extraction, floodplain drainage, sedimentation of beels and backwaters, pesticide run-off, and the degradation of slow-moving wetland habitats on which this species depends. Population trend is listed as unknown.