Japanese Rice Fish | Oryzias latipes Care & Info

Looking for a small fish to add to your (community) aquarium, but feel like guppies or tetras are a bit too boring? Meet a lesser-known but fantastic little species that we highly recommend: Oryzias latipes, the Japanese rice fish.

Keep reading for everything you need to know about what Japanese rice fish are, how to care for them, and what they need in the aquarium!

Scientific name	Oryzias latipes
Common names	Japanese rice fish, medaka
Difficulty level	Easy
Origin	Japan

Table of Contents

Japanese rice fish natural habitat & appearance

Natural habitat

Oryzias latipes is a cool little fish that can survive in both fresh and brackish water, similar to common livebearing species such as guppies. As its name suggests, it's found in Japan, where it naturally occurs on three of the four main islands: Honshu, Shikoku and Kyushu. It's present in Hokkaido as well, but it's an introduced species there.

This fish has been found in countries like Vietnam, Korea, and parts of China as well, but some of the populations in these regions have been noted to belong to different species in the genus Oryzias. It's still not entirely clear if all the non-Japanese populations are truly Oryzias latipes.

In its natural range, the Japanese rice fish (also known locally as medaka) can be found in all sorts of shallow waters, preferably between 1-2 ft in depth. Slow-moving rivers, ponds, marshes, tide pools, and particularly rice paddies work well for them.

Although the IUCN Red List considers the Japanese rice fish to be a species of Least Concern, it does mention that the wild population size is decreasing. It notes that genetic purity is being lost as interbreeding with its cousin, Oryzias sakaizumii, becomes more common. Additionally, habitat loss due to pollution plus the introduction of non-native species like Gambusia (mosquitofish) have proven harmful.

Appearance

At a maximum size of around 1.5", Oryzias latipes isn't exactly a giant among fish. This small shoaling species can be recognized by its relatively long fins, upturned mouth, flat back, and slightly rounded belly.

Wild Japanese ricefishes are off-white to silvery in color. However, this species has been kept as a pet in Japan since at least the 17th century, so breeders have had plenty of time to create all sorts of selectively bred color variants! You can find them in orange ("Youkihi"), golden, black, pink ("Sp. Pink"), albino, white ("Galaxy"), orange-headed ("Red Cap"), blue-shimmering, and much more.

Since this species is easy to genetically manipulate, transgenic variants now also exist. Ever heard of GloFish? Yep, they did that with rice fish as well. If you live in an area where they are legal, you may come across them in glowing red, yellow, or green. They're not allowed everywhere, though—restrictions exist in states like California and Washington, as well as in some European countries.

Did you know? The Japanese rice fish is commonly used in scientific research. Scientists have thoroughly studied how it responds to toxins, genetic modification, inbreeding, and more. Heck, the species was even sent to space—and it reproduced there!

Japanese Rice Fish | Oryzias latipes Care & Info

Setting up a Japanese rice fish aquarium

Requirements

If you'd like to keep a few Japanese rice fish, you don't need a complicated aquarium set-up. A 10-gallon (long) aquarium should work fine for a small group of 5-6 fish. Make sure it has a lid, because like many aquarium creatures, rice fish jump when startled.

Keep in mind that the waters this species naturally inhabits, such as rice paddies, tend to be heavily vegetated. In the aquarium, they'll appreciate it if you go heavy on the plants. Include some floating plants to dim the light a little—these guys don't like things too bright.

Fun fact: Rice fish went through a huge popularity boom in their home country during the COVID-19 pandemic. Some varieties would sell for thousands of dollars!
Pandemic craze for Japan's 'medaka' rice fish keeps up steam

Water parameters

One thing that makes Japanese rice fish such a great choice for your freshwater aquarium is that they're hardy and unfussy. They can withstand a very wide range of water parameters, including temps down to freezing and over 100 °F! As such, they won't drop dead from small beginner mistakes.

Of course, as aquarists, we want our fish to live as long as possible and thrive in our tanks, so let's not expose them to extremes like this. Instead, you should only introduce your Japanese rice fish into a fully cycled aquarium. Keeping the pH around the neutral mark works well. A heater isn't necessary if your home stays at room temp.

As always, you should perform weekly water changes with temperature-matched water to keep your fish healthy.

pH: 7-8

Temperature: 64.5-71.5 °F (they tolerate a very wide range, but this is considered ideal)

Total Dissolved Solids: 100-400

Tankmates

Japanese rice fish are peaceful beings. They do fine in a community set-up, but it's important to keep in mind that due to their preference for lower temperatures, they don't match well with many of the popular tropical fish found in your local pet store.

You could combine these fish with "regular" aquarium species, but this would require cranking up the temperature, which shortens the lifespan of the rice fish.

As such, we prefer an unheated tank with species like:

White cloud mountain minnow (Tanichthys albonubes)
Galaxy rasbora (Danio margaritatus)
Rosy loach (Yunnanilus sp. 'Rosy')
Brachygobius gobies (brackish)
Panda Garra (Garra flavatra)
Dwarf chain loach (Ambastaia sidthimunki)
Some nerite snails (like black nerites)

And for our fellow shrimp lovers... yes, these fish are compatible with many shrimp species. You shouldn't keep them with your most expensive colonies, because they will eat baby shrimp if they can. However, in a nicely planted set-up, Neocaridina and some Caridina dwarf shrimp will thrive alongside them just fine!

Japanese rice fish diet

In the wild, Japanese rice fish are helpful to have around: they eat mosquito larvae and other small bugs, keeping ponds from becoming infested. In the aquarium, these micropredators can be fed a staple diet of small floating carnivore pellets or flakes.

You can supplement their diet using frozen or live foods, which will be greatly appreciated.

Breeding Japanese rice fish

If you're looking to try your hand at breeding fish, you've chosen the right species. Although they're not as prolific as livebearers, rice fish come pretty darn close! Healthy specimens will breed very often, although the peak tends to be in spring and summer. Provide some Java moss or spawning mops for the best results.

When they're in the mood, you'll see the males sparring with each other, while also chasing and trying to entice the females. The females respond by expelling a ball of eggs, which sticks to their anal fin and is subsequently fertilized.

The females will carry the egg ball around for a while before depositing it in fine-leaved plants. If the rice fish are the only aquarium inhabitants and the tank is densely planted, you can leave things as-is. Otherwise, it can help to move the eggs to a separate tank to hatch (after 1-3 weeks depending on temperature) and grow a bit. They might be eaten if you don't!

If the fry hatch in the main tank, they don't tend to need any help from you. If you've got them in a separate container, you can raise them on small foods like baby brine shrimp.

Buying Japanese rice fish

Although Japanese rice fish are a gem of a species, not all aquarium stores carry them. If yours doesn't, or if you're looking for a specific color variety, you might be able to ask them to include rice fish in their next order.

You can also buy a wide variety of color morphs online. The Shrimp Farm carries no less than 4 different types of Japanese rice fish. This way, you can get your fish shipped right to your doorstep—with live arrival guarantee!