Laboratory of Evolutionary Genetics

Presentation and Perception of Colors in Animals


Chromo-Biology using Japanese Model Fish – Medaka

Animals exhibit various colors and color patterns on the body surface.
Humans also express various colors in the skin, hairs, and eyes. 
How and for what purpose do these colors exist?
Do animals and humans see identical colors on identical objects?
We are addressing these questions using medaka mutants and transgenics.
Colorful medaka


The Reason We Use Medaka

Medaka spawn everyday.
The fish mature in three months in a cup of water.
Cutting-edge technologies, such as genome editing, are applicable.
Various natural populations, mutants, inbreds, and transgenics are available.
It is a member of vertebrates and should share common features with humans.
Few animals possess such excellent features as a research model.

Color Genes

Various color variants exist in medaka. Their breeding history in Japan may date back to over 250 years. Breeders continue establishing new variants, which are often traded at high prices. These strains are useful resources for identifying color genes by forward genetics. Analyses of the color genes will reveal a mechanism for body-color formation and could medically or esthetically be applied to humans.

Mate Choice

Animals mate for reproduction. Partners for the mating are not randomly chosen but carefully selected based on a certain criterion in each animal. One of the most important criteria for medaka is body color. How are the color preferences acquired? Can the preferences be altered by experiences or medical/surgical treatments? Common features may be shared between medaka and humans in establishment and maintenance of sexual preferences.
Mate Choice

Color Perception

Humans provoke colors according to relative excitation of the red/green/blue cones (trichromacy). Fish have four (or more) types of cones, suggesting better abilities for color discrimination. Although it is difficult for trichromatic humans to imagine the world perceived by tetrachromacy, studies using wild-type and colorblind medaka may open up the way. Gene therapy for colorblind patients is one of our ultimate goals. 
GFP Transgenic


Summary of Achievements

Gene Cloning

Sequence Electropherogram

The orange-red (b), color-interfere (ci), and albino (i-3) medaka are one of the oldest known color variants in Japan. These strains are mutants of the slc45a2, somatolactin alpha, and pink-eyed dilution genes, respectively. The human/mouse orthologs of slc45a2 and pink-eyed dilution are involved in oculocutaneous albinisms and racial skin-color variations.



Somatolactin alpha (SLa), which is mutated in the ci medaka, is fish-specific hormone and absent in land vertebrates. Physiological functions specific for aquatic vertebrates (e.g., osmoregulation) could be expected, but both the SLa-deficient (ci) and SLa-excess (Actb-SLa:GFP) medaka are fully viable and fertile. Their body colors are the only and distinct difference.

Unsexy Medaka

Medaka Face

Some people are regarded to be sexy, while others are not. Medaka are the same. Among color variants, ci tends to be avoided as a mating partner. The lack of SLa causes this unsexyness. Then, excessive SLa should make medaka supersexy. However, Actb-SLa:GFP is even less preferred than ci. More than enough is too much. Everything in moderation.

Sexual Preference

Okazaki Large Spectrograph

Is it really the body color which makes ci and Actb-SLa:GFP unsexy? Under monochromatic light, everything appears in the same hue and chroma (but not brightness), and the unsexyness of ci and Actb-SLa:GFP is resolved. Thus, not morphological, behavioral, or olfactory cues but color is the criterion for mate choice. The color preferences are acquired depending on surrounding fish during growth and hardly be altered after sexual maturation. 

Color Blindness

Red Colorblind Courtship

Genome editing technologies enable establishment of colorblind medaka by knocking out the cone-opsin genes. Sexual preferences of the colorblind medaka are weakened, likely because of a problem in color discrimination. As dichromatic people, the colorblind medaka would help our understanding of color vision in tetrachromacy.

Giant Medaka

Growth Hormone Transgenic

SLa is closely related to growth hormone (GH), but their roles are distinct; overexpression of SLa or GH in ci (middle) causes a change in body color (bottom) or body size (top), respectively. The GH-excess medaka is double in body weight and shows defects in gamete production. Growth would need to be suppressed when reproducing offspring.




Born in 72. Undergraduate (91-95), Master (95-99), and PhD (99-20) student at Department of Biological Science, The University of Tokyo. PhD of Biological Science. Japan Overseas Cooperation Volunteer at Lwitikila Girls' Secondary School (95-97), Assistant Professor and Research Fellow of Japan Society for The Promotion of Science at The University of Tokyo (00-05), Human Frontier Science Program Long-Term Fellow at University of Konstanz (05-09), Associate Professor (10-19) and Professor (19-) at Department of Chemical and Biological Sciences, Japan Women's University. Loves scuba diving, hot springs, alcohol drinks, and video games. A lion at home, a mouse outside. Plays the violin, rarely. 

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Other members  (in Japanese)

About Us



Laboratory of Evolutionary Genetics, Department of Chemical and Biological Sciences, Faculty of Science, Japan Women's University


Senzankan 2F, Mejirodai 2-8-1, Bunkyo-ku, Tokyo 112-8681, Japan


April, 2010

Research Fields

Genetics, Evolution, Behavior

Experimental animal

Japanese Medaka (Oryzias latipes/sakaizumii)


Color Gene, Mate Choice, Color Perception