Taxonomy & naming
Dawkinsia srilankensis was described in 1985 by Senanayake — the parenthetical authority in the current combination marks the move out of the original genus. The species was long carried as Puntius srilankensis and, before formal recognition, was treated as a subspecies of the Indian filament barb Puntius arulius. A comprehensive revision of the Puntius filamentosus group by Pethiyagoda & Kottelat (2005) confirmed it as a fully valid, morphologically distinct species within that complex.
The genus Dawkinsia was established as part of the sweeping 2012 reclassification of South Asian cyprinids by Pethiyagoda and colleagues, which dismantled the old catch-all Puntius into several phylogenetically coherent genera. The filamentosus group — characterised by the elongated dorsal-fin filaments of adult males — was assigned to Dawkinsia. The Catalog of Fishes records the valid combination as Dawkinsia srilankensis (Senanayake, 1985); any reference to Puntius srilankensis in older aquarium or ichthyological literature refers to this same fish.
Morphology
D. srilankensis reaches approximately 4 in in total length. The body is moderately deep and laterally compressed, with the general silhouette shared by the filamentosus species group. The most striking feature of adult males is the elongation of the dorsal-fin rays into filament-like extensions — a secondary sexual characteristic that gives the species complex its vernacular name and presumably functions in mate assessment.
Coloration is pale to silvery, often with a golden wash, overlaid with irregular dark blotches along the flank — the "blotched" element of the English name distinguishing it from the more uniformly marked members of the group. Fin coloration and blotch contrast are typically most pronounced in dominant males. Females are more uniformly coloured and, when gravid, noticeably deeper in the belly than males.
Habitat
The species is known from a short stretch of the Kalu River at Pallegama, on the eastern slopes of the Knuckles Hills in central Sri Lanka, at elevations of roughly 984–1640 ft. The Knuckles massif — a UNESCO World Heritage area — feeds numerous small hill rivers, and D. srilankensis occupies the fast-flowing, well-oxygenated reaches of the Kalu system where the substrate is pebbly and the water clear and largely free of silt.
The combination of elevation, rapid current, and clean substrate is characteristic of Western Ghats and Sri Lankan hill stream fishes broadly. Water temperatures in such habitats are relatively cool by tropical standards, and dissolved-oxygen levels are high. The species is not recorded from the slow, silty lower reaches of the river or from adjacent drainages, and the restricted elevation band makes it highly sensitive to any alteration of water clarity or flow dynamics upstream.
Feeding
No detailed dietary study of D. srilankensis in the wild is available in the published literature. Based on the feeding habits of the filamentosus group and comparable Sri Lankan hill-stream barbs, the species is assumed to be an opportunistic omnivore, taking small invertebrates — insect larvae, crustaceans, and worms — along with algae scraped from submerged rocks and organic detritus drifting in the current.
In captivity the fish is reported to accept a wide range of prepared and live foods without special requirements. A diet of good-quality dry food supplemented with live or frozen invertebrates (bloodworm, daphnia, brine shrimp) and some vegetable matter is appropriate for maintaining condition and colour.
Mating
Like all barbs, D. srilankensis is an egg-scattering, non-guarding spawner. Courtship consists of a driving male pursuing a gravid female through fine-leaved vegetation or across the pebbly substrate, the two pressing together briefly as eggs and milt are released simultaneously. There is no pair bond and no territory is maintained beyond the brief courtship sequence.
The elongated dorsal-fin filaments of males likely play a role in intrasexual competition and female choice, consistent with secondary sexual ornaments seen across the filamentosus group. Colour and finnage intensity typically peak during spawning condition. No paternal or maternal care follows spawning, and adults will consume eggs they encounter.
Breeding
Captive breeding of D. srilankensis follows the pattern established for the filamentosus group. A separate, shallow spawning tank with slightly acidic to neutral, well-oxygenated water, fine-leaved plants or a spawning mop, and a mesh or marble-layer bottom to protect scattered eggs from the adults is the standard setup. A well-conditioned pair or small group is introduced, and spawning typically occurs in the morning.
The adhesive eggs fall to the bottom or catch in plant material; the adults should be removed promptly, as they will eat eggs given the opportunity. Hatching follows in approximately one to two days at appropriate temperatures, and fry become free-swimming a few days later. First foods are infusoria or commercial fry preparations, transitioning to newly hatched brine shrimp as the fry grow. Successful captive propagation is important for the species given its Endangered status in the wild and the impracticality of wild collection.
In the aquarium
Dawkinsia srilankensis is a specialist aquarist's fish rather than a staple trade species. Its endemic status, Endangered listing, and restricted natural habitat mean it is rarely encountered commercially, and any specimens in the hobby are likely captive-bred. It is best kept in groups of six or more, which reflects its shoaling nature and distributes any intraspecific chasing across the group.
The natural habitat — cool, fast, well-oxygenated hill-stream water — should be replicated as closely as possible: strong filtration, a high rate of water movement, pebbly or sandy substrate, and temperatures in the cooler part of the tropical range (around 68–75 °F). A pH of 6.0–7.5 and soft to moderately hard water are appropriate. The fish are reportedly hardy feeders once settled, accepting dried, frozen, and live foods. Long-finned or very slow tankmates are best avoided.
Conservation
Dawkinsia srilankensis is assessed as Endangered (EN) on the IUCN Red List under criteria B1ab(iii)+2ab(iii), reflecting a very small and severely fragmented extent of occurrence. The species is known from only a few kilometres of the Kalu River at Pallegama, and the area of occupancy is similarly tiny.
The primary identified threat is siltation caused by upstream gem-mining operations — tailings entering the river and smothering the pebbly, silt-free substrate on which the species depends. Habitat degradation from mining has been noted in multiple sources observing the population. The combination of extreme range restriction, a single known river system, and an active and ongoing threat makes any further deterioration of water quality or substrate condition potentially catastrophic for this species. Captive propagation and the safeguarding of its small watershed are the most realistic conservation levers available.