Japanese Rice Fish Care: Breeding, Diseases, Tank Setup

So you’re probably trying to tame different species of Japanese rice fish, then you’ve come to the right place. Personally from experience, I think that the Japanese rice fish are beautiful and easier to breed, and do not need much more care, so if you’re a beginner at taming fish then this one could be for you.

Japanese rice fish are a very interesting group of species containing up to 3 dozen species of small fish which are spread all around the world. Japanese rice fishes are usually found in freshwater but can also survive in brackish and also marine environments.

This article will tell you about the beautiful rice fish along with its specifications, breeds, growth factors, tank requirements, nutrients, and foods.

To know more about Japanese rice fish, keep reading as you will explore more interesting things about it.

About Japanese rice fish

Japanese rice fishes are a very interesting group of species containing up to 3 dozen species of small fish which are spread all around the world. Japanese rice fishes are usually found in freshwater but can also survive in brackish and also marine environments.

The usual common species is known as Medaka. They can be differentiated by their orange goldish color scales and some of them have blue eyes. One main characteristic that makes them unique is that their scales glow in the dark. The gold and moonlight medakas are the most famous kind bred for taming.

Naturally, we can find Japanese rice fish in rice paddies in Japan. Japanese rich fishes are very easy to take care of and are compatible with living with other tameable fishes. That’s why these fishes are kept by many aquarists in their aquariums. Raising these fishes is very easy but they need a special environment to be raised and bred.

Average Lifespan Of A Japanese Rice Fish

Japanese rice fishes are very playful and non-aggressive fish that can live with other non-aggressive fishes. In a home aquarium, a Japanese rice fish can live up to 3-4 years

Sex: Sexual Differences

The sexual diversity of a Japanese rich fish is not so highlighted but the females are seen to have smaller fins as compared to their male counterparts. Males have more of a triangular fin. Also, females have a more round belly while males have a flatter and longer one. Males tend to be more colorful than females. Similarly, males consist of a small bump on the body in front of the anal fin.

Sizes And Body

An average adult Japanese rice fish can grow up to 3.5 cm to 1.5 inches in length. These fishes come in various body colors thus making them beautiful when light hits on their scale reflecting variations of color.

Factors Affecting Fish Growth

Even though Japanese rice fish are hardy animals there are some factors that affect their natural growth. Factors such as average water temperature, cold climate, level of nutrients, and presence of other metals in water affect the growth of Japanese rice fish.

Tank Setup

Japanese rice fish do not necessarily require large tanks, the minimum requirement of a tank is up to 10 gallons for a school of 6. Normally they are found in shallow rivers, rice fields, and ponds so adding plants with enough sunlight is recommended. The plants also somewhat prevent the fishes from jumping out of the tank.

Japanese rice paddies are the natural environment for rice fishes so it would be optimal to create a similar natural environment for these fishes to live in. Apart from the environment, you’ll need to invest in a good heater and filtration unit to maintain the health condition of the Japanese rice fish. You will also require a translucent lid that can cover the fish as well as provide them with enough sunlight.

Since these fishes are very active, Medakas tend to jump around the aquarium so adding a lid is important. A spongy lid could be good so the water can be enriched with air.

Tank Size

The Japanese rice fish, or medaka, is a small, hardy species that does well in captivity. They are active swimmers and do best in a tank with plenty of room to swim around.

A good rule of thumb is to provide 1 gallon of water per fish. So, for a school of 5 medakas, you would need a 10-gallon tank. If you plan to add more fish to your school, just increase the tank size by 1 gallon for each additional fish. Medaka is easy to care for and makes a great addition to any freshwater aquarium.

Plants We Can Use Inside The Tank

Aquarium plants such as Moneywort, Hornwort, Rotala Rotundifolia, Pygmy Chain Sword, Hygrophila Polysperma, Cryptocoryne Wendttii, Anubia Nana, Java Fern, and many more can be used to fill your tank. This also helps in keeping the tank water fresh, clean, and full of nutrients. You could consider adding floating plants like red root floaters or water lettuce to give your ricefish some shade.

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What Type Of Water Do Japanese Rice Fish Prefer?

Japanese rice fish plants usually live in freshwater so the tank must have enough supply of freshwater. A good filtration system should also be installed considering that Japanese rice fish cannot survive in dirty water. Calm water is best as their natural habitat is located in shallow ponds and rivers.

Water Parameters

Japanese rice fish are prone to fresh water so you need to consider the weekly water changes to guarantee healthy water conditions. Also, make sure to dechlorinate your tap water before putting it in your tank. Tap water consists of chlorine and metals that could harm the growth of Japanese rice fish.

Ph Level Of Water

The recommended pH level of water is 7.0 to 8.0.

Hardness Of Water

Japanese rice fish prefer to live in fresh cold water. They are referred to as hardy fishes so these fishes can pretty much live in any health condition of the water. 5-25 dKH level of hardness of water is to be maintained.

Temperature Of Water

Rice fish are referred to as cold water fishes so no heater is required for the tank. Cold water is preferred by aquarists. 61 to 75°F water temperature is suitable for Japanese rich fish’s habitat. However, high temperatures of water can cause damage to the internal organs of the fish so installing a water heater is necessary for the tank.


Good filtration equipment is required to keep the tank water clean as the Japanese rich fish prefer fresh clean water and strive in dirty unclean water.

I would personally recommend investing in a good filtration system just because they help in keeping the water clean and helps in maintaining the nitrogen levels of the water.

A normal sponge filter will work great but if you really want to invest in a good filtration system for keeping many fishes in a single community then I would recommend upgrading to a canister filter. These types of filters will create very little flow in water, which is ideal for these fishes because they prefer living in shallow ponds having calm water.


Mostly any type of substrate can be good to keep. These substrates will be a good housing factor for healthy bacteria to grow for the fish. Substrates without any sharp and pointy edges will be alright. I would suggest you add any good aquarium soil just in case you’d like to plant the tank later.

Tankmates Of Japanese Rice Fish

Japanese rice fish are small fishes so it’s necessary to avoid big fishes that may look at them as prey. Try to choose fishes that are similar to their size and habits like them. which means that fishes that can adapt to similar situations rice fishes live in.

Popular tank mates of Japanese rice dishes are:

  • Fancy goldfish
  • White cloud minnows
  • Endler’s livebearers
  • Celestial pearl danios
  • Asian stone catfish
  • Adult shrimp
  • Nerite snails

How Often Does The Tank Need To Be Cleaned?

The tank needs to be cleaned every 1 or 2 weeks according to the school size. A healthy tank is required for the good physical growth of Japanese rice fish as a healthy environment and healthy water are necessary for the growth of rice fish.

What Types Of Food do They Eat?

Japanese rice fishes aren’t very picky animals. Therefore, they will basically eat anything keeping in mind their small size.

These rice fishes are omnivores, so they consume both plants and organisms. Medakas can consume any type of diet containing pellets, granules, or flakes. Pellets need to be crushed into smaller pieces before being fed. Apart from that organisms and small animals are also an important part of their diet and need to be provided as a supplement. Which keeps them fit and healthy.

Breeding Japanese Rice Fish

If you want to breed Japanese rice fish commercially, I prefer you to just breed the rice-fish in the tank rather than with other fish. The other fishes might eat the eggs unless you have many plant thickets. Breed them in a tank that is covered with many floating plants. They prefer to lay eggs in those plants or bushy areas.

The breeding mainly occurs during the spring and summer seasons. During this period the males fight for their territory and attract females. Then the female will lay eggs which will be fertilized by the male. The female after a few minutes will lay those eggs after finding a safe place.

The incubation period takes several weeks or faster if the perfect conditions are met. The hatched fry can be fed infusoria or liquid dry food.

Diseases Of Japanese Rice Fish

Japanese rice fishes are resistant to most diseases but that doesn’t mean that they are 100% resistant to all diseases. It depends on how you care for the tank and purify the water. For that, you need to be careful what you add to the water because adding harmful bacteria can cause infection to grow in the fish.

However the infection isn’t immediate, you can detect the infection in one or two weeks by noticing weird behaviors in Japanese rice fishes.

In poor water conditions, you might be able to detect ich diseases in some Japanese rice fishes as a result of stress. They may also develop fin rotting in extreme water conditions. Other than that these fishes are very strong and resilient animals.

To prevent any type of disease you need to keep the tank and water clean by changing the water regularly and installing a good filtration unit. You should also maintain a healthy diet that’s full of nutrients that the fishes need.

How To Maintain Temperature And Ph Levels Of Tank Water?

The optimal temperature for a Japanese rice fish is 61-75°F. Even though Medakas are known to live in colder climates, putting them in colder water for a longer period can cause their lifespan to degrade. So, investing in a heater is necessary to maintain the water temperature.

Ph range for Japanese rice fishes to live is 7.0-8.0. Therefore it is necessary to check the water regularly to maintain the PH levels. While using unsuitable water, we could use an osmosis or deionization system to get the ideal water quality.

When To Move Between Tanks With Increase In Population?

A pair of 6 fishes can reproduce up to several hundred fries. Therefore it is necessary to keep moving them into larger tanks as these fishes increase in number. What I do is that I breed them in my 10-gallon tanks for a few weeks. Then as they get nearly 1.5 inches long I migrate them into a much larger tank(30-gallon) so the school can increase their number with ease.

Are Japanese Rice Fish Aggressive?

Japanese rice fish are not aggressive. However, they start to get anxious(jumping out of the tank when left alone. So keeping a good bunch of them or keeping them with other similar species of fish is recommended.

Medakas get along with other tankmates very easily.


Can Rice Fish Be Kept As A Pet?

Japanese rice fish are non-aggressive, fun little animals that are beautiful in looks too. So keeping them as a pet is a good idea as we can see their playful nature as they swim around the tank which is obviously enjoyable to watch.

Can They Be Bred On Small Pots With Plants?

Since Japanese rice fishes are very small they can be basically bred anywhere but if you want to breed them in small pots then I would recommend using some kind of lid or cover so you can save them from the sunlight. It also prevents them from jumping out of the pot.

Are Japanese Rice Fish Attacked By Other Fishes?

If you keep them with their corresponding tank mates then there will be no problem with that. But do not keep them with fishes that would find them as a good meal.

Fishes I don’t recommend keeping them with:

  1. Bettas
  2. Pufferfish
  3. Angelfish
  4. Tiger barb
  5. African cichlids
  6. Oscars

How Often Do We Clean Japanese Rice Fish’s Tanks?

Japanese rice fish are a popular type of aquarium fish, known for their peaceful nature and elegant swimming style. As with any pet, however, they need to be properly cared for in order to stay healthy and thrive. One important aspect of care is maintaining clean water conditions.

While the frequency of water changes will vary depending on the size and stocking level of the tank, as a general rule, it is recommended to perform a partial water change (25-50%) once a week.

This helps to remove built-up waste and replenish essential nutrients in the water. In addition, be sure to vacuum the gravel and clean the filter media on a regular basis. By following these simple steps, you can help ensure that your Japanese rice fish have a clean and comfortable home.


Medaka fish is the best fish to keep if you want to start breeding fish and their eggs. These fish are easy to take care of and also flourish under normal water conditions.

Basic necessities are enough to keep them healthy and increasing in size. So if you want a pet that’s pleasant to have and doesn’t require too much babysitting then Japanese rice fish is the one to go for.