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Oryzias latipes var.
Rare medaka with greenish external light. Unlike the usual silver-white, the green external light creates a unique atmosphere. Rare and popular with collectors.
Ryokukou (Green Light) medaka is a rare improved variety with a distinctive greenish external body light, unlike the usual silver-white of Miyuki-lineage medaka. The green light emanating from the back, as the name suggests, creates an atmosphere found in no other variety. The special direction of iridophore light reflection is thought to produce this green external light. Highly rare and particularly popular among collectors. Dark top-viewing containers best showcase and reveal the green external light. Selecting individuals with strongly greenish external light maintains the Ryokukou characteristic, though fixation is difficult and requires patient selection work. Easy to breed with spawning mats.
The Ryokukou Medaka lives 2-3 years.
The Ryokukou Medaka grows to 3-4cm.
The ideal temperature for the Ryokukou Medaka is 20〜28℃.
Hardy in 5–30°C, neutral to slightly alkaline water.
Origin
Japan (selectively bred variety)
Lifespan
2-3 years
Size
3-4cm
Temperature
Sources: FishBase: Oryzias latipes / Seriously Fish: Oryzias latipes
Selectively bred killifish are trait combinations of body form × body color × pattern × luminescence (internal/external) × scale types (transparent scales) × sparkle × fin morphology and so forth. Published entries include only confirmed traits constituting the given variety, with genetic inheritance patterns provided only for confirmed traits (uncertain cases omitted). Genetic patterns are provided as reference for breeding.
Sources: JMA Japan Medaka Association — Improved Medaka Variety Classification Manual (JA) / Improved Medaka Web Encyclopedia (medakazukan, JA)
A curated selection of notable morphs. Inheritance modes are a breeding-planning guide; actual appearance varies with combos.
Edited & verified by: BreederDirect editorial team
The taxonomic, regulatory, and husbandry data on this page are compiled and verified against the authoritative primary sources below.
Accepted name: Oryzias latipes var. (Temminck & Schlegel, 1846)
Synonyms: Aplocheilus latipes (Temminck & Schlegel, 1846), Poecilia latipes Temminck & Schlegel, 1846, Oryzias latipes latipes (Temminck & Schlegel, 1846)
Authority databases: FishBase · GBIF · Japan Medaka Association — Variety Classification Manual (JA)
Nomenclature follows global taxonomic authority databases.
Find listings for this species
5〜30℃
Medaka pellets, daphnia
Black top-viewing container shows green external light best
5-30°C (optimal 20-28°C)
Natural light makes green shimmer more vivid
Ryokukou trait has slightly lower inheritance — selection important
Rare variety — may be difficult to obtain
Intermediate. This is an intermediate-level species. Some prior experience and knowledge of environmental management are recommended.
The ideal temperature for Ryokukou Medaka is 20〜28℃. Avoid sudden temperature changes and maintain a stable environment.
The average lifespan of Ryokukou Medaka is 2-3 years. With proper care and nutrition, they can live a long and healthy life.
Ryokukou Medaka typically reaches 3-4cm as an adult. Size may vary depending on care conditions and individual genetics.
Ryokukou Medaka feeds on: Medaka pellets, daphnia. Aim for a balanced diet with appropriate feeding frequency.
The price of Ryokukou Medaka varies significantly depending on morph, size, and lineage. Check our market price page for the latest pricing information.
Last updated: August 31, 2026