How difficult is it to keep Mellor Medaka?

Intermediate. This is an intermediate-level species. Some prior experience and knowledge of environmental management are recommended.

What is the ideal temperature for Mellor Medaka?

The ideal temperature for Mellor Medaka is 18〜28℃. Avoid sudden temperature changes and maintain a stable environment.

What is the lifespan of Mellor Medaka?

The average lifespan of Mellor Medaka is 2-3 years. With proper care and nutrition, they can live a long and healthy life.

How large does Mellor Medaka get?

Mellor Medaka typically reaches Up to about 4cm SL as an adult. Size may vary depending on care conditions and individual genetics.

What should I feed Mellor Medaka?

Mellor Medaka feeds on: Prepared medaka food, green water. Aim for a balanced diet with appropriate feeding frequency.

What is the typical price for Mellor Medaka?

The price of Mellor Medaka varies significantly depending on morph, size, and lineage. Check our market price page for the latest pricing information.

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Mellor Medaka

Intermediate

Oryzias latipes

An improved medaka whose fins split into several parts because the fin membrane is missing. Created in 2013 by Yukio Oba, the trait first appeared on the tail alone, but line breeding produced fish showing it on every fin.

Difficulty

Intermediate

Temperature

18〜28℃

Lifespan

2-3 years

Size

Up to about 4cm SL

Diet

Prepared medaka food, green water

About

Merah, also written mellor, is the trait in which each fin divides into several parts. The Medaka Web Encyclopedia groups it with the fin traits, explained in line with the Japan Medaka Association classification manual. It was created in 2013 by Yukio Oba: growth of the fin membrane stops partway, so a fin splits into as many parts as there are gaps in the membrane. When first found the trait showed only on the tail, but line breeding produced fish carrying it on every fin. Some fish also stop growing fin rays partway, and those whose fins still reach normal size are regarded as the better specimens. Two other traits also multiply the fins: samurai, formerly selfin, which divides only the dorsal or anal fin and tends to appear on the hikari and hikari-daruma body types, and choki. Merah is distinguished by appearing on every fin and on the standard and daruma body types as well. Certified new varieties of the Japan Medaka Association include fujin, a white merah (No.19, Yukio Oba), and raijin, a yellow merah (No.21, Ryota Matsumoto).

Source: Wikipedia (CC BY-SA 4.0)

Lifespan of the Mellor Medaka

The Mellor Medaka lives 2-3 years.

Size of the Mellor Medaka

The Mellor Medaka grows to Up to about 4cm SL.

Temperature & humidity for the Mellor Medaka

The ideal temperature for the Mellor Medaka is 18〜28℃.

Basic Info

Origin

Japan (a trait created in 2013 by Yukio Oba)

Care Specifications

pH: 7–8
Hardness (GH): 9–19 dGH
Water Temp.: 18–28℃

PeacefulGroupBreeding: Moderate

Sources: Medaka Web Encyclopedia: Complete Medaka Care Guide / FishBase Oryzias latipes / Medaka Web Encyclopedia: Merah (split fins)

Morphs (Varieties)

The Japan Medaka Association's classification manual sorts varieties by traits that can be seen rather than by genotype, and does not set out how individual traits are inherited. Traits the manual explicitly says can be passed on and produced by selective, multi-generation breeding are listed as line-bred; the rest are grouped under Other.

Other

Merah (split fins)Pink merahMerah with swallow

Sources: Japan Medaka Association: Variety Classification Manual, 5th ed. (Sep 2025) / Medaka Web Encyclopedia: Medaka Traits / Medaka Web Encyclopedia: Merah (split fins) / Japan Medaka Association: List of Certified New Varieties

A curated selection of notable morphs. Inheritance modes are a breeding-planning guide; actual appearance varies with combos.