Japanese Ricefish Care Guide: Tank, Feeding and Breeding

Written By Lewis German  |  Temperate Fish  |  0 Comments

Japanese ricefish/medaka

What are Japanese Ricefish?

Ricefish, or Medaka are a small species of fish that can live in a variety of conditions, and are often found in a variety of environments, including flooded marshes, wetlands, forested streams and pools.

Ricefish are able to tolerate a wide range of conditions and are even able to live in brackish water.

Where are Japanese Ricefish from?

Despite their name, Ricefish are not exclusive to japan, and are actually found in numerous locations across South East Asia, including parts of Eastern China, Korea and Taiwan.

They are found in a wide range of habitats, from small flooded pools, to streams and rivers, as well as brackish canals.

Do Japanese Ricefish need a heater?

Japanese Ricefish do not need a heater if they are being kept in the home aquarium, as they are well adapted to live in temperate and cold water conditions.

These fish do have their limits however, and should not be kept in temperatures that are too cold.

The areas these fish naturally live in are subject to mild winters, where they are well protected from severe temperature dips.

For this reason, it is recommended to avoid letting your Ricefish drop below 15C / 59F.

Can Japanese Ricefish live in a tropical aquarium?

It is possible to keep Ricefish in a tropical aquarium too, and in fact, they are a great option for small, peaceful community tanks due to their hardiness, ease of care, small size and passive nature.

They will however, struggle at high temperatures, and are best kept below 25C / 77F, as they may become irritable, stressed, and will have a higher metabolic rate in warmer temperatures.

Can Japanese Ricefish live in an outdoor pond?

There is much debate as to whether or not Ricefish can be kept in an outdoor pond year round.

For some people, it is completely possible to house and even breed Ricefish outdoors, even if you live in an area that receives a high amount of snow in the winter.

However, for others, cold spikes and ice can wipe out their Ricefish colony.

So how can you tell if you are able to keep Ricefish outdoors or not?

Essentially, if you only receive a mild winter, your pond is large, well insulated, and is situated in an area that protects it from harsh weather, the chances are your Ricefish will survive.

However, it is still possible for a dip in temperature to take them out, and so it is recommended that you either place a heater in your pond, or further insulate it to protect the fish.

You ideally want to keep a figure above 10C / 50F if possible, you may go up or down by a couple degrees, but if you want the maximum survival rate for your fish, it is best to stay within a safe range.

How large do Japanese Ricefish grow?

Ricefish are small, and generally only grow to around 1.5” in length, making them an ideal nano fish.

Their small size allows them to be kept in smaller planted aquariums, and allows you to keep them with very small tankmates, such as young fry, shrimp and other nano fish.

This size can work to their detriment however, as they would make an easy meal for any fish with a large mouth, so be careful as to not house them with larger tankmates.

What size tank do Japanese Ricefish need?

Ricefish can live in a range of tank sizes, and can be kept in a tank as small as 5 gallons.

However, we personally recommend a minimum tank size of 10 gallons, as in smaller tanks, the males can become quite territorial.

Having the extra space also allows you to keep a fair sized group of Ricefish, a necessity as these are a highly social schooling species.

Water parameters for Japanese Ricefish?

pH7 – 8
HardnessModerate KH and GH
Temperature15C – 24C (59F – 76F)
Ammonia (NH3)0 ppm
Nitrite (NO2)0 ppm
Nitrate<5 ppm

What to feed Japanese Ricefish?

Ricefish will try to eat almost anything, and are typically not fussy eaters by any means.

However, their small mouths can only fit tiny foods, and so you may need to accommodate for this by offering small particulate foods, in the form of powders, crushed up flakes and baby Brine Shrimp.

Ricefish will also do well if fed on veggie based foods, such as algae wafers and green flakes.

Be sure to offer them a good variety, as they are omnivorous by nature.

Can Japanese Ricefish live with Goldfish?

We don’t really recommend keeping Rice Fish with Goldfish, as they are small enough to be easily swallowed by larger fish.

It is possible to keep young Goldfish that are smaller than 3”  with Japanese Ricefish, but any larger and they will be at risk of being swallowed.

So while they can be kept with baby Goldfish for a time, we do not recommend keeping these fish together long term.

Best tankmates for Japanese Ricefish?


Guppies are ideal with Ricefish, they are a similar size, temperament and have very similar needs to the Japanese Ricefish.

Both can be kept at a high pH, and can live at around 24C / 76F, which is ideal, as you wont need to struggle to find a middle ground in water parameters for both species.

Zebra Danios

Danios pair well with Ricefish, because again, they are very similar in size, temperament, and have similar care needs.

Neither of these fish need to live in a heated tank, and can be kept in coldwater or temperate setups comfortably, allowing you to keep them in an unheated community tank.

Bronze Corydoras

Peaceful, hardy, and able to be kept in a room temperature setting, Bronze Cories are great with Japanese Ricefish.

They inhabit the lower level of the tank, and will mop up any uneaten food that the Ricefish leave.

They pair particularly well as Ricefish offer low competition when it comes to feeding, and your Cories will easily receive enough food, something which is often an issue in many other community setups.

How to sex Japanese Ricefish?

Ricefish have been bred into a number of varieties today, and depending on the variation or the breed you get, can influence the difficulty when it comes to sexing the fish.

Generally however, there are a few subtle differences between male and female Ricefish that set them apart, and will allow you to easily identify them.

First off, males are generally larger than females, they are more slender, longer, and taller, possessing an arched back, and having elongated dorsal and anal fins, which can sometimes be decorated with colours or a spiked texture.

Females are smaller, rounder, and more plump than the males, they are often lighter in colour, and have shorter fins.

If you manage to spawn your Ricefish, you will notice the females sometimes carrying their eggs in a clutch around their anal fin, which is a key indicator that your fish is indeed a female.

How to breed Japanese Ricefish?

Ricefish are very easy to breed, and are a great fish to start with when you are first getting into breeding egg layers.

To start, you must condition your fish by feeding them well over a period of around 2 weeks, this helps give them the nutrition they need to spawn, and allows the females to generate eggs.

After this period, you may notice that the fish flare up in colour, the males may begin to spar over territory, and the fish will seem much more focused on chasing each other around, and cleaning up areas ready for spawning.

To initiate a spawn, increase the temperature over a period of days, and then perform a partial cold water change.

Buffering the water can also help induce spawning, as an influx of minerals can bring the fish into condition.

For the next few days your fish will spawn early in the morning, just before the sun comes up.

To release their eggs, the females will carry them to a location they perceive as being safe, usually where there is a high amount of dense plantlife, and they will stick them to a leaf or carpet of moss.

They will then leave them and will no longer show any more parental behaviour.

Ricefish are often cannibalistic, and will eat their own eggs and young, unless they are moved to another tank and raised separately.

The eggs will take around 2 – 3 days to hatch depending on the temperature, and once born, the fry will need to be fed infusoria, live baby brine shrimp and crushed flakes 3 times a day.

After around 2 months of growth, the young should be large enough to move back in with their parents without much issue.