Ryusei Medaka

Ryusei Medaka key facts

Care level

Intermediate

Lifespan

2-3 years

Size

Up to about 4cm SL

Temperature

18〜28℃

Diet

Prepared medaka food, green water

Lighting

Since the sheen runs unbroken from head to tail, the variety is made for viewing from above, and a dark container makes the line of light stand out. The Medaka Web Encyclopedia recommends outdoor keeping and notes that summer sun raises water temperature sharply, suggesting shade such as a reed screen over half the container.

Diet & Nutrition

Commercial prepared medaka food is the staple, given in an amount finished within a few minutes. Leftovers decay and foul the water, so adjust the quantity. Green water rich in phytoplankton suits fry rearing.

Water Temperature & Quality

Slightly acidic to slightly alkaline water is considered ideal, and the water drifts toward acidic as keeping continues. Around one water change per week is the guideline, and because sudden shifts in temperature or pH cause stress, acclimatise new fish by floating the bag. FishBase records the wild water chemistry of this species as pH 7.0-8.0 and hardness 9-19 dH.

Tank Mates & Compatibility

A peaceful schooling fish, normally kept as a group of the same variety. One litre of water per fish is the guideline against overcrowding; overstocking causes poor growth, reduced breeding, oxygen shortage and water fouling.

Breeding

Outdoors the spawning season runs from about April to October, once water reaches 18C or above with 12-13 hours of daylight. For year-round indoor breeding, 25-28C water and over 13 hours of lighting are the guideline. Eggs hatch at a cumulative 250 degree-days, about 10 days at 25C.

Health & Notes

The maruko body type has no dorsal fin, so swimming posture is less stable and strong flow should be avoided. The key point in grading is whether the sheen breaks where the dorsal would sit; fish retaining a trace of the fin fall outside the standard. Outdoors the fish become inactive and overwinter near the bottom as water cools, resuming activity in spring once daytime water exceeds 10C. A 0.3-0.5% salt bath is used for ailing fish, with water raised to no more than about 28C.

About Ryusei Medaka

Ryusei Medaka pairs a finless Marco body with Miyuki-line body glow that runs unbroken from head to tail. Bred in 2013 and certified as the Japan Medaka Association's third recognized variety, it suits intermediate keepers.

7 things to know before welcoming a Ryusei Medaka

1. 1A Finless, Marco Body Shape

   Ryusei belongs to the Marco lineage, a line of medaka bred without a dorsal fin, giving it a distinctly different silhouette from standard medaka. Because there's no dorsal fin to interrupt it, the body glow appears to flow unbroken along the back from head to tail.

2. 2Glow Varies From Fish to Fish

   How far and how brightly the body glow extends differs from one individual to the next. Watching the coloration and glow develop as the fish matures is part of the appeal of keeping Ryusei.

3. 3Best Suited to Intermediate Keepers

   Ryusei is generally considered a variety for intermediate keepers. Coming to it with some experience in basic medaka care, such as water changes and temperature management, makes it easier to keep them stable and thriving.

4. 4Grows to About 4cm

   Adults reach a maximum standard length of around 4cm. Plan your tank or container with this full-grown size in mind so there's enough room as they mature.

5. 5A Named Variety Since 2013

   Ryusei was developed in 2013 by Yoshinori Nakazato and registered as the third officially certified variety of the Japan Medaka Association. That gives it a clearly documented origin as a distinct line.

6. 6Light and Water Quality Shape Its Glow

   As with other hikari (body-glow) varieties, sunlight exposure and water quality are said to influence how vivid the glow appears. Keeping them somewhere they get natural light, such as outdoors or on a covered balcony, tends to bring out their color more clearly.

7. 7Pick by Looking at Each Fish

   Because body shape and how far the glow extends vary between individuals, it's worth looking closely at the actual fish before bringing one home. Every Ryusei has a slightly different look, which is part of the fun of choosing one.

Frequently asked questions about Ryusei Medaka

Q.Where does the name "Ryusei" come from?

A.Because Ryusei has no dorsal fin, its body glow runs in one unbroken line from head to tail, and the fish appears to trail light like a shooting star as it swims. The variety was developed and named by Yoshinori Nakazato in 2013.

Q.How is Ryusei different from Miyuki medaka?

A.In Miyuki, the body glow is interrupted where the dorsal fin sits, but Ryusei's finless Marco body lets the glow flow along the back in one continuous line. The glow itself still traces back to the Miyuki lineage.

Q.Is Ryusei suitable for beginners?

A.Ryusei is generally regarded as a variety for intermediate keepers. It's easier to keep them stable if you already have some experience with basic medaka care, like water changes and temperature management.

Q.How large does Ryusei grow?

A.Adults reach a maximum standard length of around 4cm. It's a good idea to choose a container with enough room to spare for this full-grown size.

Q.Can Ryusei be kept with other medaka varieties?

A.They can be housed together without issue, but if you're planning to breed them, crossing with other varieties can dilute Ryusei's distinctive body shape and glow pattern over generations. If you want to preserve the line, it's best to breed Ryusei with Ryusei in a separate container.

Useful tools for Ryusei Medaka care

Learn more about Ryusei Medaka in the encyclopedia

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