Introduction to Medaka Selective Breeding

Medaka selective breeding is one of the most fascinating hobbies for enthusiasts. The joy of creating your own varieties with beautiful body colors, elegant fin shapes, and unique body forms is unparalleled. Today, there are said to be over 500 varieties of improved medaka, with new breeds continuing to emerge every year.

This article explains the basic knowledge that those interested in medaka selective breeding should know first.

Characteristics That Can Be Modified Through Medaka Selective Breeding

In medaka selective breeding, the following characteristics can primarily be modified:

Body color: Medaka body color is determined by a combination of multiple chromatophores. - Black chromatophores (melanophores): contain black pigment - Yellow chromatophores (xanthophores): contain yellow to orange pigment - White chromatophores (leucophores): reflect white pigment - Iridescent chromatophores (iridophores): reflect light to produce iridescent and metallic luster

By genetically manipulating the presence or proportion of these chromatophores, diverse varieties are born such as Yōkihi (orange), Mikuki (bluish-white luster), Kōtei (red), and Orochi (deep black).

Body shape: In addition to normal body type, there are variations such as Daruma (short body type), Hikari body type (light enters the back), long fins, and Swallow (elongated fins).

Fin shape: There are breeds with variations in fin length and shape, such as Matsui long fins, Tennyo no Mai, and Mela.

Basic Knowledge of Genetics

To conduct selective breeding, it is necessary to understand the basic mechanisms of heredity.

Dominant and recessive traits: Most medaka traits follow the laws of dominant and recessive inheritance. For example, normal body color is dominant over Yōkihi body color. When crossing an individual with dominant traits and an individual with recessive traits, all F1 (first generation) individuals will display the dominant trait, but in F2 (second generation), the recessive trait will reappear with a probability of one in four.

Homozygous and heterozygous: When an individual possesses both copies of a gene in the same form, it is called homozygous; when possessing different forms, it is called heterozygous. Since recessive traits require homozygosity to be expressed, "fixing homozygosity" becomes an important point in selective breeding.