Taxonomy & naming
Bleeker described the species in 1854 in a different genus, and it now sits in Oryzias; the authority is therefore in parentheses. The name refers to Java. It is often confused with other brackish-water ricefishes of the region, and records outside the Malay region are best treated with caution.
Morphology
A small, transparent ricefish with the typical Oryzias profile; FishBase gives a maximum of 2 in TL.
Habitat
Mangrove creeks, estuaries, tidal ponds and coastal drainage canals of western Indonesia, the Malay Peninsula and neighbouring coasts, including the Panimbang River on Java, the type locality. FishBase also lists ditches and canals, and says it stays at the surface where aquatic plants grow densely. It gives a pH range of 7.5 to 8.5 and a temperature range of 22 to 25 C.
Feeding
Takes small crustaceans, insects and protozoans from the surface, and fine prepared foods in captivity.
Mating
Males are slightly larger finned than females and display near a female before spawning.
Breeding
The female carries her eggs in a cluster attached to the genital pore by filaments, then attaches them to fine plant material. FishBase reports it as a non-annual breeder. Incubation time has not been published.
In the aquarium
FishBase describes it as very difficult to maintain in aquaria, and it is not seen in markets. It suits a small brackish tank, though it will also live in fresh water. Feed small live foods and keep it with other small, peaceful fish. The lid should fit.
Conservation
The IUCN Red List assessed Oryzias javanicus as Least Concern in 2018. It is widespread, though mangrove and estuarine habitat is being lost across the region.