General Information
The Medaka (Oryzias Latipes) is a freshwater fish that thrives in temperate water and originates in East Asia. Medaka are commonly called rice fish because they're often found in rice paddies across East Asia, especially Japan, Vietnam, Laos and eastern China.
Medaka Lifespan
The lifespan for a Medaka is around 3 - 4 years if cared for accordingly.
In the wild, Medaka only have a life expectancy of around one year. In captivity, they can live three to four times as long if conditions are optimal and they don't get sick.
Please keep in mind that caring for an animal for such a long time is a big commitment and consider if you really want and can do that.
Appearance
Medaka Size
The very small size (up to 1.5 inch / 3.8 cm) and hardiness of Medaka have made them a popular pet fish since the 17th century.
The final size of an adult Medaka also depends on their genetics and the type and amount of available food sources. The more food is available, the more the animal will max out on its potential growth.
Make sure to provide adequate food for your Medaka, but don't over- or underfeed as this brings its own problems. You can find more information on feeding below.
Medaka Colors
Medaka come in many different colors such as white, yellow, black, blue, brown, albino, and many additional color variations achieved through crossing medaka with different colors.
Medaka Shape
Medaka can have different body shapes depending on the breed: normal figure, dharma figure, semi-dharma figure, hikari figure.
The original shape of a Medaka is called "normal" figure.
Medaka with a dharma figure have a more rounded body shape.
Rice fish that have semi-dharma figure are shorter than the normal Medaka, but longer than dharma-shaped Medaka.
Hikari shape is characterized by a diamond-shaped tail fin.
Water and Tank Requirements
Medaka Water Temperature
Medaka are temperate water fish, which means they enjoy temperatures that fall between cold and tropical water temperatures, with optimal conditions between 59 °F (15 °C) and 82 °F (28 °C).
Medaka Water Parameters
Although Medaka can survive a wide variety of water temperatures between 40 - 108 °F (6 - 42 °C), it's best to keep them in temperate water (see above). This means that you can keep them in your aquarium without a heater, which differentiates them from other small freshwater aquarium species like Panda Garra. Ph levels should be between 7 and 8, with a water hardness of 50 - 300pm and 5 - 10 KH.
Medaka Tank Size
Every Medaka should have at least 2 gal (6 l) of water to themselves. So, if you want to keep 6 small Medaka, there should be at least 10 gal (36 l) in your tank.
Please keep in mind that your aquarium hardscape also takes away from the overall water volume in your aquarium and that if you plan to add other fish to the tank you need even more water!
The calculated water amounts shouldn't be shared between species but always added up.
Medaka Tank Requirements
Small groups of Japanese Ricefish can be kept in nano tanks, but a larger tank or mini pond is always preferable. They enjoy planted environments with a lot of cover (i.e. floating plants) and a dark ground. Since they can jump out of the tank you should always cover your aquarium with a lid.
Behavior and Tank Mates
Medaka are friendly towards their own and other species. This means they can be housed with other types of fish that are also generally friendly and have similar water and tank requirements.
Please note that even the most peaceful species can get aggressive when they feel threatened, e.g., when there is too little space in the tank or they have to fight with others for a limited food supply. Please always make sure to meet the requirements of your animals as closely as possible to avoid such issues.
Medaka should be kept in groups of at least 6 animals. If kept in a smaller group they might get anxious and lethargic.
Medaka are very social animals and like to spend most of their time swimming close to their group. They can be kept with other non-aggressive fish species of similar size, as well as shrimp and snails and will mostly ignore those other species.
Medaka are generally non-aggressive and peaceful but active swimmers. Research has shown that they are capable of complex social interaction, recognize individual members of their herd and adapt their behavior according to the relationship they have with them.
Fish generally don't sleep the same way mammals do and how exactly they sleep is still a topic of research. It is clear though, that they also have periods of rest where they move less and their metabolism is reduced.
Feeding
Japanese Ricefish are omnivores and enjoy a varied diet of flakes or pellets, as well as live or (dry) frozen Artemia or microworms. They also need some plant matter in their diet but usually won't touch aquarium plants. We have had great success with feeding our Medaka sera ImmunPro Mini Nature (affiliate link).
Breeding
Medaka need enough clean water and nutrition to reproduce. Medaka are easy to breed in an aquarium during the time between spring and autumn. Females spawn on a daily basis, mostly during the first hours of daylight. After fertilization, the eggs are attached near the anal fin of the female before she deposits them on plants. After fertilization, the fish should be removed from the aquarium in order to prevent them from eating the eggs.
If you want to learn more about how to hatch Japanese Rice Fish eggs and raise the fry, check out our blog article on hatching Medaka eggs.
Common Problems
- short lifespan: Due to their relatively short lifespan you will have to breed them or buy new fish regularly in order to keep your herd going.
- disease: Medaka are generally very hardy fish but they are suspectibel to ich (white spot disease). Always keep the aquarium clean and well-maintained to avoid this problem.
Fun Facts
- salt and freshwater: In the wild Medaka can easily move between freshwater and salt water without any health problems.