Japanese Rice Fish (Oryzias latipes): Care Guide


Common Name(s)Japanese Rice Fish
Scientific NameOryzias latipes
OriginJapan, Laos, Vietnam, Taiwan, eastern Korea, eastern China
Temperature61-72°F (16-22°C)
Size1.5 inches (4 cm)
Minimum Tank Size10 gallons
Food & DietOmnivorous micropredator
Lifespan4 years
Water pH7.0-8.0
Tank MatesPeaceful fish of similar size
BreedingSpawns adhesive eggs near vegetation.
DiseaseWhile they are resilient fish, they may be susceptible to Ich.
Japanese Rice Fish
Japanese Rice Fish (Oryzias latipes)

Japanse Rice Fish Care

The Japanese Rice Fish (Oryzias Latipes) or Medaka, has been a popular pet fish for aquarists because of its small size, hardiness and colorful appearance. They also go by many names, Japanese Killifish, Japanese Medaka, and Rice Fish There are a variety of Japanese Rice Fish, the most popular being the Gold Medaka and the Moonlight Medaka. The Gold Medaka have been kept in aquariums since the 17th century and are famous for their orange and gold color. The Moonlight Medaka on the other hand are a newer breed and are known for their silver color. Neither the Gold Medaka nor the Moonlight Medaka can be found in the wild. Wild Medaka naturally have a bland color.

Medaka are native to East Asia and can be found in rice paddies and ponds. They can also travel from freshwater to saltwater environments so it’s not uncommon to find them in the ocean. Due to their hardiness to multiple environments, they have been thoroughly researched. In fact, they reached space aboard the space shuttle Columbia in 1994 to be further studied.

Are Japanese Rice Fish right for me?

The Japanese Rice Fish is great for beginners since they do not require much maintenance compared to other types of fish. Rice Fish do not need a heated aquarium and only a basic sponge filter is needed to keep the water clean.

Their natural habitat are shallow rivers and ponds so they can live in a wide range of conditions and require minimal cleaning. In fact, it is common to have the Rice Fish outside with no heating. These fish are peaceful so adding other fish of a similar size and nature to your aquarium is possible. Japanese Rice Fish are widely available and inexpensive.

Tank Setup

Rice fish do not require large aquariums, at least a 10 gallon tank is needed for a school of 6 fish. Naturally Rice Fish reside in rice paddies, shallow rivers and ponds so adding plants and sunlight to your aquarium is recommended. In Japan it is also common to keep Rice Fish in a ceramic bowl just outside the home.

Clean water is also important to Rice Fish so you will want to change the water on a regular basis and add a good sponge filter system if you have an indoor aquarium. If your setup is outdoors with indirect sunlight and plants you will not need a filtration system. Air stone or sponge filters are best for setups with harsh sunlight.

In the wild Rice Fish move from freshwater to saltwater so either is acceptable for your aquarium setup. You may want to use freshwater in your setup as it is easier to maintain and freshwater will be better for the aquarium plants.

Keep in mind that ponds and shallow rivers are their natural habitats so keep your setup with calm water. You can use plants like Pistia and Water Hyacinth which will provide plenty of cover and a great breeding ground for your fish.

Rice Fish tend to leap out of their aquariums, putting a lid on your setup can be a good idea. A spongy lid with an air hole can help with the water and air quality.

Japanese Rice Fish Temperature & PH

Japanese Rice Fish are very durable and can withstand a lot. The ideal temperature is between 61-72°F (16-22°C) with a pH level between 7.0 – 8.0. The cooler temperatures can extend the lifespan of the fish.

If the ideal temperature is not possible in your setup, Rice Fish can live in waters anywhere between 3 – 42 °C (37 – 108 °F). Aquarium heaters are not recommended for any setup as the water can easily get too hot for your fish.

It is best to test the water every two weeks to a month to maintain the water quality. You can use a reverse osmosis or deionization system to get the ideal water quality.

Food & Diet

Japanese Rice Fish are omnivores by nature so flakes and freeze-dried food from a pet store is common. Occasionally, you can also feed them worms, mosquito larvae, small vegetables, and artemie saline. Feeding them at least twice a day is recommended.

Rice Fish are not aggressive and do not eat other fish, instead they eat the organisms that live in their mouth. Although live food has many of the nutrients they need, keep in mind that they are plant eaters first so feeding them live food should be sporadic.

How To Care For Japanese Rice Fish – Everything You Need To Know About Medaka Fish

Japanese Rice Fish Tank Mates

Naturally, Rice fish are small, peaceful fish so they can be tank mates with other peaceful fish but be aware it is not recommended to put larger fish (even if they are peaceful) as they can still show aggression towards the Rice Fish.

Keep in mind that Rice Fish are small, usually only 4 cm in length so they like to stay in schools to feel safe. They are very social fish and can even recognize the faces of other Rice Fish. When thinking of having tank mates for your Rice Fish choose peaceful fish that are the same size. It is rare for Rice Fish to show any aggression so adding a predator fish will be seen as a threat.

Breeding Japanese Rice Fish

Japanese Rice Fish will often lay eggs during spring and summer time. Rice Fish prefer to lay their eggs in grassy areas for cover so having an aquarium with plenty of bushy plants will be the optimum conditions for breeding.

If you are planning to breed your Rice Fish you’ll need to make sure that the water temperature is ideal (16-22 °C). The plants in your aquarium are crucial to the breeding process as they provide cover for the fertilized eggs. Java moss and spawning mops are good for breeding.

At first it may be difficult to identify the sex of the fish you have but male Rice Fish have have extended anal fins where as females do not. Once the eggs have been fertilized they will stay with the female until they get attached to the plants in your aquarium. It takes between 10 to 12 days for the eggs to hatch. Newly hatched fry will feed off infusoria and later baby brine. The new fry can grow quite quickly as it can take only a couple of weeks for them to grow.

If your fish are having trouble breeding you can feed them bloodworms or similar food to help them start breeding.

Japanese Rice Fish Diseases

In a well maintained aquarium disease is not an issue for the Japanese Rice Fish. However they are not immune to disease and can happen in ill maintained tanks or by the addition of fish and plants.

Although Rice Fish only need regular care, health problems and diseases can arise from dirty tanks or by the addition of fish or objects into the tank. To help prevent disease in your tank make sure you replace at least 30% of the water on a regular basis. Also if you are going to add plants, decorations or any other objects into your tank make sure you clean them before putting them in the water.

Having a good filtration system will also help prevent the spread of any bacteria in the water. A well-balanced healthy diet can also help your Rice Fish stave off any disease. A healthy well-maintained habitat keeps your fish happy and healthy ready to fight off disease. One positive thing about the Rice Fish is how strong and resilient they are. Often with other types of fish, when disease has entered the aquarium it can infect all the fish before any warning signs show up. For Rice Fish, disease does not easily spread and often can be caught before wide spreading can occur.

The first sign of disease is when the fish starts to show odd behavior. If you happen to notice this in your tank consult with your local pet store on treatment and clean your tank thoroughly.

Japanese Rice Fish Lifespan

The lifespan of the Japanese Rice Fish is up to 4 years. For the longest life possible make sure that the habitat is under optimal conditions including a healthy diet.

Although Rice Fish are easy to take care of and require minimal care, regular maintenance and monitoring is needed for a long and happy life. As discussed earlier in this article optimal habit conditions and a healthy diet will produce the best quality life for your fish.

The natural habitats are ponds, rice paddies and shallow rivers so the closer your home setup replicates those conditions the happier your fish will be. Make sure to monitor the pH level and temperature of your water and make the necessary changes.

Hopefully this article brought insight into the Japanese Rice Fish. Whether you are a beginner or an experienced aquarist the Rice Fish will be a great addition to your aquarium.

Fish Laboratory

With decades of collective fishkeeping experience, we are happy to share the knowledge that we've picked up along the way. Our goal at Fish Laboratory Aquatics is to keep publishing accurate content to help fishkeepers keep their fish healthy.

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