Taxonomy & naming
Hamilton described the species in 1822 in his survey of the fishes of the Ganges, and it now sits in Oryzias; the authority is therefore in parentheses. Most laboratory literature has used the name Oryzias melastigma for the marine medaka, which is treated as a synonym of O. dancena in the Catalog of Fishes.
Morphology
A small, slender ricefish with a translucent body and a series of dark spots along the upper flanks and the base of the anal fin. FishBase gives a maximum of 1 in SL.
Habitat
Estuaries, tidal creeks, mangroves, brackish ponds and coastal rice paddies from India and Bangladesh to Myanmar. The type locality is the Calcutta botanical garden area in the Ganges estuary. FishBase says it usually occurs near the coast but also lives in fresh water as well as brackish habitats, and it tolerates a wide range of salinity.
Feeding
Takes small crustaceans, insect larvae and algae from the surface and the water column. In captivity it accepts small live foods and fine prepared foods.
Mating
Males show larger dorsal and anal fins and display close to a female before she spawns. Courtship is similar to other Oryzias.
Breeding
As in Oryzias generally, the female carries a small egg cluster at her vent for a time and then attaches it to fine plant material. Incubation time has not been published for this species.
In the aquarium
Suited to a small brackish tank, though it will live in fresh water as well. Offer live baby brine shrimp and fine foods, and keep it with other small, peaceful fish. A lid is needed.
Conservation
Not threatened as a species in the usual sense. It is common in coastal Asia, and the IUCN Red List assessed it as Least Concern in 2019.