Oryzias minutillus – Dwarf Medaka
Oryzias minutillus was described by Smith in 1945. The name Oryzias comes from ancient Greek and means rice. The fish of this genus are often found in rice fields. Minutillus is derived from Latin, minutus means small. Their common name is Dwarf Medaka.
As the name suggests, the Dwarf Medaka is a small-growing species. They can reach a maximum length of about two centimeters. The body is semi-transparent with the spine visible. The eye, nose and flank show an iridescent blue color.
The difference between the males and females can be seen in the fins. The anal fin of the male is rounded outwards (convex), that of the females is rounded inwards (concave). The females are also slightly larger than the males.
Oryzias minutillus can be found in slow-flowing or stagnant rivers and creeks, but also in flood plains and rice fields. They are found in Cambodia, China, Laos, Myanmar and Thailand.
In the wild, the Dwarf Medaka is a micro-predator. They prey on small insects, invertebrates, worms etc. In the aquarium it is an easy eater. They eat live and frozen food, flakes, granules, etc. Keep in mind that this is a small fish and therefore also has a small mouth.
Due to the small size of the Dwarf Medaka, they are not really suitable for the community aquarium. They are quickly mistaken for prey.
You can keep them as a school in an aquarium from 40 centimeters in length. Set up the aquarium with a dark bottom, lots of plants and some swimming space for them to come forward. With a somewhat dim light you can see the iridescent spot on the flank and the eye better than in a too brightly lit aquarium.
The water for the Oryzias minutillus aquarium may have a temperature between 23 and 32 degrees Celsius. They like fairly neutral to slightly more acidic water values, a pH of 6.0 to 7.5. The GH may be between 2 and 15.
Breeding Oryzias minutillus – Dwarf Medaka
The breeding of the Dwarf Medaka is not too difficult, but it is best done in an aquarium with only this species. Spawning usually takes place in the morning. The male defends a small territory in the water column and lures a female. In the water column, the female deposits the eggs that are directly fertilized by the male. The clump of eggs sticks to the female for a while. She looks for a place where she can safely hide the eggs. Usually between fine-leaved plants. In the aquarium you can also use a spawning mop or, for example, Java moss.
The temperature of the water determines how long it takes for the eggs to hatch. This varies from one to three weeks. The parents usually leave the eggs alone. However, the newly hatched young DOryzias minutillus are prey. After depositing the eggs, it is therefore best to remove them or move the parents to another aquarium. You can feed the newly born fry with micro-worms and later also with freshly hatched brine shrimp.
Note, the young fish are micro hunters. If you have several generations of fry, they will hunt their younger brothers and sisters. Growing several generations in the same aquarium has its limitations.
John de Lange
Nonn Panitvong – Siamensis.org