Order : Cypriniformes
Family : DANIONIDAE
Species : Boraras maculatus
Standard Length (excludes tail) : 2.5 cm
(Fishbase 2026)

The genus Boraras contains, as of 2026, just 6 valid species, all of which occur in Southeast Asia (Fishbase, 2026).

Boraras maculatus (Pygmy Rasbora, Dwarf Rasbora, Spotted Rasbora) inhabits slow-moving, shallow, acidic forest streams in freshwater swamp forest and peat swamp habitats in Peninsular Malaysia, Singapore, Sumatra and the Riau Islands (with unconfirmed records from Surat Thani [Thailand] and Kalimantan [Borneo]). (IUCN - Ahmad, 2019).

In the field it is easily overlooked due to its small size, but once located its identity is easily confirmed by its pinkish-orange colour and by the presence of a prominent, circular dark spot on each flank (this feature can help distinguish it from the larger Harlequin Rasbora). Its dorsal and anal fins are red with black margins, and there is a small dark spot at the base of the anal fin and tail fin.

This tiny species, of less than 3 cm length, often occurs in mixed shoals with other, larger species of rasbora.

A study of disconnected/isolated acidic water habitats in Peninsular Malaysia concluded that despite there being significant genetic divergence between different populations of Boraras maculatus, as a result of millions of years of isolation, there was little apparent change in their morphology (i.e. their internal and external structure, appearance and patterning). The study concluded that this was a case of 'morphological stasis in a stenotopic miniature species' (Fam et al, 2024).

Fig 1 : Pygmy Rasbora in freshwater swamp forest habitat in Singapore.

Fig 2 : Trio of Pygmy Rasbora next to a Forest Betta (Betta pugnax) in Singapore.

Fig 3 : Typical habitat of Boraras maculatus - a shallow, silty, acidic stream with leaf litter detritus in freshwater swamp forest.

Fig 4 : A lone Pygmy Rasbora with a much larger Einthoven's Rasbora (Rasbora einthovenii) in Singapore.


References and links :

Ahmad, A.B. 2019. Boraras maculatus. The IUCN Red List of Threatened Species 2019: e.T169519A89800398.

Fam, Y. Q., Jamaluddin, J. A. F., Muhammad‐Rasul, A. H., Ilham‐Norhakim, M. L., Rosely, N. F. N., & Lavoué, S. (2024). Contrasting genetic and morphological differentiation among geographical lineages of a stenotopic miniature rasborine, Boraras maculatus, in Peninsular Malaysia. Journal of Fish Biology, 104(1), 171-183.

Ho Jonathan K. I., Sorain J. Ramchunder, Andrew Memory, Meryl Theng, Li Tianjiao, Esther Clews, Cai Yixiong, Tan Heok Hui & Darren C. J. Yeo. (2016). A Guide to the Freshwater Fauna of Nee Soon Swamp Forest.  Singapore: Lee Kong Chian Natural History Museum & Tropical Marine Science Institute, National University of Singapore. 139 pp.

Fishbase - Boraras maculatus