Medaka Ricefish (Oryzias latipes)

A hardy, peaceful temperate nano fish that thrives in planted aquariums, unheated indoor tanks, and seasonal outdoor tubs.

The Medaka Ricefish, Oryzias latipes, is a small and highly adaptable freshwater fish known for its peaceful temperament, surface-oriented behavior, broad temperature tolerance, and straightforward breeding.

Unlike many common aquarium fish that require consistently tropical temperatures, Medaka can thrive in normal room-temperature aquariums and often do not require a heater. Their adaptability also makes them especially suitable for planted tanks, shallow aquariums, and seasonal outdoor container setups.

Selective breeding has produced an enormous variety of ornamental Medaka strains, including orange, white, black, metallic, sparkling, longfin, and highly reflective forms. While colour and finnage may vary between strains, their general aquarium requirements remain very similar.

Why Medaka Ricefish Stand Out

• Hardy and highly adaptable freshwater nano fish
• Often suitable for aquariums without a heater
• Peaceful and easy to keep in groups
• Excellent for planted aquariums and shallow tanks
• Well suited to seasonal outdoor tubs and container ponds
• Small adult size of approximately 3–4 cm
• Easy and fascinating egg-laying breeding behavior
• Available in many selectively bred ornamental colour strains
• Excellent choice for both beginners and experienced breeders

Best For

• Unheated indoor aquariums
• Planted nano tanks
• Seasonal outdoor tubs
• Beginner aquarists
• Medaka breeding projects
• Peaceful community aquariums
• Aquarists looking for small temperate fish in Canada

Topick Aquarium Insight

One of the biggest advantages of Medaka is that they do not need to be treated like a typical tropical aquarium fish.

In a temperature-controlled home, a heater is often unnecessary. Maintaining them permanently at very warm tropical temperatures is also usually unnecessary. A stable room-temperature aquarium can be an excellent environment for this species.

Medaka are especially enjoyable in shallow planted aquariums because they naturally spend a large amount of time near the surface. Their behaviour is easy to observe from above, which is also one reason many ornamental Medaka strains are selected for strong top-view colour and metallic reflection.

Their hardiness should not be confused with indestructibility. Stable water quality, regular maintenance, appropriate feeding, and gradual temperature changes are still important for long-term health.

What Is a Medaka Ricefish?

Medaka is the widely used aquarium name for Oryzias latipes, a small freshwater ricefish associated with shallow ponds, wetlands, irrigation channels, slow-moving waterways, and other calm lowland habitats.

The name “ricefish” comes from the close association of these fish with shallow agricultural waterways and similar habitats.

Medaka are not guppies or livebearers. They belong to the ricefish family Adrianichthyidae and reproduce by laying eggs.

They are sometimes compared with killifish because of their small size and surface-oriented behavior, but Medaka belong to a different fish family and have their own distinctive reproductive biology.

Does Medaka Need a Heater?

In many indoor aquariums, no.

Medaka are temperate fish and tolerate a substantially wider temperature range than most tropical aquarium species. A normal indoor room temperature is often perfectly suitable.

A heater may still be useful if the aquarium is located in an unusually cold room or somewhere with large and rapid temperature fluctuations. The goal should be suitable and reasonably stable conditions rather than simply keeping the water as warm as possible.

For routine aquarium keeping, approximately 18–26°C is a practical range. Healthy, gradually acclimated Medaka can tolerate temperatures outside this range seasonally, but sudden temperature changes should always be avoided.

Can Medaka Live Outdoors in Canada?

Medaka are excellent seasonal outdoor fish during suitable weather in Canada.

Outdoor tubs can provide natural sunlight, algae, microorganisms, insect prey, and seasonal temperature variation. Under appropriate conditions, Medaka often grow and reproduce extremely well outdoors.

However, “cold tolerant” does not mean that Medaka can automatically be left outdoors through every Canadian winter. Small tubs and containers may freeze completely, and temperature conditions vary greatly between regions and setups.

We recommend treating most small outdoor Medaka setups in Canada as seasonal unless the aquarist has a properly designed overwintering system and understands the local climate.

Behavior & Group Size

Medaka are peaceful social fish that spend much of their time in the upper portion of the aquarium.

They are not extremely tight schooling fish, but they naturally associate in loose groups and behave much more confidently when several are kept together.

We recommend keeping at least 6 Medaka, with 8–10 or more preferred when aquarium size allows.

Larger groups also distribute normal social and breeding interactions across more individuals rather than concentrating attention on one fish.

Tank Setup

Medaka do not require an elaborate aquarium. A mature planted setup with calm water, surface cover, and plenty of horizontal swimming space works extremely well.

• 10 gallons or larger recommended for a small group
• Long or shallow aquariums work especially well
• Gentle to moderate filtration
• Avoid excessively strong current
• Floating plants provide useful surface cover
• Fine-leaved plants are excellent for breeding
• Spawning mops can be used for easy egg collection
• Leave open surface area for feeding and swimming
• A secure lid is recommended because Medaka can jump
• A mature, biologically stable aquarium is preferred

Heavy water movement is unnecessary. Medaka naturally suit shallow, quiet, or gently moving water and usually show more relaxed behavior when they are not constantly fighting strong filter flow.

Water Parameters

• Scientific Name: Oryzias latipes
• Common Name: Medaka Ricefish
• Family: Adrianichthyidae
• Adult Size: approximately 3–4 cm
• Temperature: approximately 18–26°C for routine aquarium keeping
• pH: approximately 6.5–8.0
• Hardness: adaptable; moderate mineral content works well
• Temperament: Peaceful and social
• Swimming Level: Upper to surface level
• Diet: Omnivore / micro-predator
• Care Level: Beginner

Medaka are highly adaptable compared with many ornamental nano fish. Stable water, regular maintenance, good oxygenation, and appropriate feeding are more important than constantly adjusting the aquarium to reach one exact pH value.

Feeding

Medaka have a naturally upturned mouth and are particularly well adapted for feeding near the surface. They readily accept a wide variety of appropriately sized foods.

• High-quality floating micro pellets
• Fine or crushed flakes
• Baby brine shrimp
• Daphnia
• Cyclops
• Mosquito larvae from safe sources
• Small frozen foods
• Small live foods
• Natural microorganisms available in mature outdoor tubs

Small floating or slowly sinking foods are particularly suitable because Medaka naturally spend a large portion of their time feeding close to the water surface.

A varied diet containing quality dry foods together with occasional live or frozen foods supports growth, breeding condition, and stronger natural coloration.

Tank Mates

Medaka work best with peaceful fish that tolerate similar temperatures and will not outcompete or prey on them.

• Other compatible Medaka strains
• Small peaceful ricefish
• Peaceful nano fish with overlapping temperature requirements
• Small Cory-type catfish that tolerate the selected temperature
• Freshwater snails
• Amano Shrimp
• Adult Neocaridina Shrimp

Avoid aggressive fish, large predators, and species that require permanently high tropical temperatures.

Temperature compatibility is just as important as temperament when selecting tank mates for Medaka.

Shrimp Compatibility

Adult Neocaridina and Amano Shrimp generally coexist well with Medaka in planted aquariums.

However, Medaka are opportunistic micro-predators. Newly hatched shrimplets are small enough to be eaten if discovered.

If maximum shrimp reproduction is the goal, a dedicated shrimp aquarium remains the better choice.

Male vs Female Medaka

Mature Medaka can usually be sexed by comparing body shape and fin development.

• Males: generally show a slimmer body with longer or more pronounced dorsal and anal fin development
• Females: generally become fuller through the abdomen, particularly when carrying developing eggs

Sexing becomes considerably easier once fish are mature and in good condition.

Breeding

Medaka are one of the most enjoyable small freshwater fish to breed.

After spawning, a female may temporarily carry a visible cluster of fertilized eggs attached beneath the abdomen. She later deposits or brushes these eggs onto fine-leaved plants, floating plant roots, spawning mops, or other suitable surfaces.

This unusual behavior makes it easy for breeders to identify spawning females and collect eggs.

Eggs can be moved into a separate hatching container to reduce the risk of adults eating them. Depending on temperature, development usually takes approximately one to two weeks.

Newly hatched fry are extremely small and initially require fine foods such as infusoria, powdered fry food, or other suitable microscopic foods before progressing to freshly hatched baby brine shrimp.

Why Are Medaka Popular for Outdoor Tub Breeding?

Medaka are naturally well suited to shallow water and surface feeding. Outdoor containers can provide many of the conditions that encourage strong growth and reproduction.

Natural sunlight supports algae and microorganism growth, while small insects and other live foods may become available naturally. Floating plants also provide shade, cover, and excellent egg-laying surfaces.

Outdoor setups should still be monitored carefully. Protect tubs from overheating, predators, pesticides, contaminated rain runoff, excessive evaporation, and sudden water-quality changes.

Medaka vs Guppy

Medaka and guppies are both small, peaceful aquarium fish, but they are biologically and behaviorally very different.

• Medaka: egg-laying ricefish, highly tolerant of temperate conditions, often suitable without a heater
• Guppy: livebearer that gives birth to fully formed fry and generally prefers warmer, more mineralized tropical conditions

Medaka are often a better option for aquarists specifically looking for a small fish for a room-temperature aquarium.

Medaka vs Killifish

Medaka are sometimes described as killifish-like because they are small, surface-oriented egg layers. However, Medaka are true ricefish belonging to the family Adrianichthyidae and should not be treated simply as another killifish species.

Their breeding behavior, environmental tolerance, and long-established ornamental strains make Medaka a distinct aquarium group of their own.

Keeping Different Medaka Strains Together

Different ornamental Medaka strains can usually live together because their basic care requirements are similar.

However, different strains can interbreed. If maintaining a specific colour, metallic, longfin, or pattern line is important, each breeding strain should be kept separately.

Mixing varieties is perfectly acceptable for a display aquarium when preserving strain genetics is not a goal.

Canada-Wide Live Fish Shipping

Medaka Ricefish are available from Topick Aquarium in Canada when in stock. Local pickup is available in Markham, Ontario, and Canada-wide live fish shipping may be available depending on weather, route, and livestock condition.

Important Note

Medaka are hardy and temperature tolerant, but sudden environmental changes can still cause stress. Always acclimate fish carefully and avoid rapid changes in temperature or water chemistry.

Outdoor keeping in Canada should be planned according to local weather. Small containers should not automatically be considered safe for winter because they may freeze completely.

Ornamental Medaka strains can vary in colour, metallic coverage, fin shape, body pattern, and appearance from above. Unless specifically listed as WYSIWYG, product photos should be considered representative rather than an exact image of every fish sold.

FAQ

What is a Medaka Ricefish?
Medaka Ricefish is the common aquarium name for Oryzias latipes, a small, peaceful and highly adaptable freshwater ricefish.

Does Medaka need a heater?
Often no. Medaka are temperate fish and usually perform very well at normal indoor room temperatures. A heater may still be useful if the room becomes unusually cold or experiences rapid temperature changes.

What temperature is best for Medaka?
Approximately 18–26°C is a practical range for routine aquarium keeping. Healthy Medaka can tolerate broader seasonal temperatures when changes occur gradually.

Can Medaka live outdoors in Canada?
Yes during suitable seasonal weather. Outdoor tubs can work extremely well in spring, summer, and early fall. Winter survival depends heavily on local climate and setup, so small outdoor tubs should not automatically be considered safe for year-round keeping.

How big do Medaka Ricefish get?
Most adults reach approximately 3–4 cm.

How many Medaka should I keep?
We recommend at least six, with groups of eight to ten or more preferred when aquarium size allows.

Can Medaka live in a 10 gallon aquarium?
Yes. A mature 10 gallon aquarium can house a small group when filtration and maintenance are appropriate. Larger aquariums provide greater stability and space for bigger groups.

Are Medaka beginner-friendly?
Yes. Their adaptability, small size, peaceful behavior, simple feeding requirements, and straightforward breeding make them an excellent beginner fish.

Are Medaka coldwater fish?
Medaka are better described as temperate fish. They tolerate cooler water than most tropical aquarium species, but they should not automatically be treated like fish designed for freezing or extreme cold conditions.

Do Medaka breed easily?
Yes. Mature females regularly carry visible egg clusters and later attach the eggs to plants, roots, or spawning mops. Eggs can easily be collected for separate hatching.

Are Medaka livebearers?
No. Medaka lay eggs. Females may temporarily carry the fertilized eggs externally before attaching them to plants or other surfaces.

Can Medaka live with shrimp?
Adult freshwater shrimp are generally compatible. Very small newborn shrimplets may still be eaten opportunistically.

Can different Medaka colours live together?
Yes for display purposes. However, different strains can interbreed, so separate breeding colonies are recommended if maintaining a specific strain is important.

Do Medaka jump?
They can. A secure lid or well-protected aquarium edge is recommended, especially in shallow setups where fish spend most of their time near the surface.

What should I feed Medaka?
Small floating or slowly sinking foods work particularly well, including micro pellets, fine flakes, daphnia, cyclops, baby brine shrimp, and other appropriately sized live or frozen foods.

Is Medaka good for an unheated aquarium?
Yes. Medaka are one of the better small freshwater fish for a stable room-temperature aquarium and often do not require additional heating.