Oryzias mekongensis – Mekong Ricefish

Oryzias mekongensis or Mekong Rice Fish only grows to about three centimeters long. You can keep them in a group of at least 8 in an aquarium from 40 cm.

Oryzias mekongensis – Mekong Ricefish

Oryzias mekongensis was described in 1986 by Uwa and Magtoon. The genus name Oryzias is derived from the ancient Greek oryza meaning rice. This is because the species from this family also occur in the rice fields. The species name mekongensis is derived from the origin of this species, the Mekong River.

They are part of the family Adrianichthyidae or the Rice fish. This family has two genera and about 37 species. It is possible that a number of species have now become extinct due to habitat loss.


The Mekong Rice Fish is not very big. They can reach a total length of up to 2.5 to 3 centimeters. The color of this fish is brown/gray with transparent fins. Males have a bright orange stripe on the top and bottom edge of the caudal fin. This dash is missing or is much less visible in the females. The body is slender and elongated with a relatively large eye.


The habitat of Oryzias mekongensis is in Asia. To be more precise in the Mekong River basin in Cambodia, Laos, and Thailand. They inhabit the shallow non-flowing streams, streams, channels, and pools. They are most common in parts with many fine-leaved plants.


This small micro predator mainly feeds on plankton, worms, small invertebrates. Very small animals that live between the plants. You can feed Oryzias mekongensis in the aquarium with flakes, very small granules, frozen or live food. Please make sure the food is small enough to eat. In general, it is not a picky eater.

The Aquarium

The aquarium for a school of Oryzias mekongensis does not have to be very large. From 40 centimeters for a minimum school of about eight copies is sufficient. In a smaller group, they feel uncomfortable and languish.

Provide a densely planted aquarium and some fine-leaved plants. A dark substrate and some floating plants are certainly appreciated. It dampens the light a bit, making them more visible. The temperature may be between 23 and 27 degrees Celsius at a pH of 6.0 to 7.5.

With a length of up to three centimeters, it goes without saying that you cannot combine them with fish that are too large. You can combine them perfectly with shrimps such as Caridina or Neocaridina. Small and more peaceful Gouramies are also an option. You can also think of the smaller and more peaceful species such as Boraras and Trigonostigma.

Breeding Oryzias mekongensis

This small fish is very prolific and fairly easy to breed. Females in good condition can produce a small number of eggs every few days (or even every day).

Usually, they spawn early in the morning. The male defends a small territory and chases other males away. He tries to seduce the females to spawn. His colors darken when trying to attract females.

When they mate, the female releases a clump of eggs. These remain attached as a nugget on the genital opening of the female. Then they are directly fertilized by the male. The clump of eggs lingers for a while until the female can hide the eggs between fine-leaved plants such as Java moss or Cabomba.

Raising the fry

The incubation period of the eggs depends on the temperature. They hatch after about one to three weeks. Although the Mekong Rice Fish parents often do not eat the eggs, this does not apply to wriggling fry. These are immediately seen as food. In a very densely planted aquarium, a young fish will occasionally survive, but most fish do not make it.

If you want to breed with Oryzias mekongensis, a separate breeding aquarium is necessary. Use some water from the parents’ aquarium and move the eggs here. You can feed the young fish with very fine food such as micro worms. Once they are slightly larger, you can also give freshly hatched brine shrimp.

Pay attention! It is a micro hunter. Young fish larger than their younger brothers and sisters will see them as food! Everything that moves and fits in the small mouth is eaten.



John de Lange

Copyright images

Nonn Panitvong – siamensis.org


Description and Karyotype of a new Ricefish, Oryzias mekongensis from Thailand.

Additional information





First described by

Hiroshi Uwa, Wichian Magtoon


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