Blue-Eye Medaka
Blue-Eye Medaka is a medaka whose pupils (the dark part of the eye) look blue. The blue comes from guanine appearing in the cornea and does not affect body color or scales. In our breed guide, the name refers to this trait itself or to black-bodied strains that carry it. They are small medaka, and they make a charming sight schooling together in a tank or medaka container. Care difficulty is rated beginner-friendly, so they suit first-time medaka keepers. How the blue looks can change with lighting and from fish to fish, so it helps to check photos or videos before you bring one home.
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Blue-Eye Medaka key facts
- Care level
- Beginner-friendly
- Lifespan
- Few reliable data
- Size
- About 3-4 cm (wild medaka reach up to 4 cm SL: FishBase)
- Diet
- Omnivore (floating prepared foods, live foods such as daphnia)
- Container & Tank
- Eye colour is easiest to see up close from the side; the black body has no background adaptation, so it stays dark in glass tanks.
- Breeding
- In outcrosses only about 17% of F1 showed the trait; pair fish with clear blue in both eyes.
- Tank Mates & Compatibility
- Peaceful and fine with other medaka of similar size. To keep the variety's traits, do not let it breed with other varieties in the same container.
- Diet & Feeding
- Give floating food that is eaten within 3-5 minutes: at least twice a day in summer, once a day in spring and autumn, and little or none outdoors in winter.
- Cautions
- Never release ornamental medaka into rivers, ponds or paddies; hybridisation causes genetic pollution of wild medaka.
About Blue-Eye Medaka
Blue-Eye Medaka has pupils that look blue due to guanine in the cornea, without changing body color or scales. Small and beginner-friendly. Care tips and FAQs included.
7 things to know before welcoming a Blue-Eye Medaka
1Why the eyes look blue
The pupil (the dark part of the eye) looks blue because guanine appears in the cornea. This does not affect body color or scales, so the blue is limited to the eyes.
2Check the body color
Our breed guide describes the name as covering either the blue-pupil trait itself or black-bodied strains that carry it. Naming can differ from one seller to another, so check the photos and description, and send a message if anything is unclear.
3Looks vary with light
How blue the eyes appear can change with lighting, viewing angle, and the individual fish. Ask the seller for several photos or a short video before you decide, so you know what to expect when it arrives.
4Beginner-friendly care
Care difficulty is rated beginner-friendly. They are small medaka. Start with a container that has room to spare and prepare dechlorinated water. When changing water, avoid big temperature differences.
5Prevent jumping out
Medaka can leap out of the water when startled, so cover the container with a lid or netting. Leave some space between the water surface and the rim, and close any gaps.
6Feeding and water changes
Give small medaka-sized food in small amounts, only what they finish. Leftovers foul the water. When the water gets dirty, replace part of it rather than all at once, which helps keep conditions stable.
7Acclimation and monitoring
On arrival, float the bag to even out the temperature, then mix in your tank water little by little (acclimation). Over the next few days, watch swimming, fins, and appetite, and move any fish that looks off to a separate container to observe. If anything about the eyes worries you, ask the seller.
Frequently asked questions about Blue-Eye Medaka
- Q.Are the blue eyes a sign of illness?
- A.Our breed guide describes it as a trait in which guanine appears in the cornea, making the pupil look blue. If you notice cloudiness or swelling in the eye, or anything else that looks off, ask the seller about it.
- Q.Can a beginner keep them?
- A.Care difficulty is rated beginner-friendly. They are small, so with a lidded container, dechlorinated water, and care not to overfeed, they are approachable even for first-timers.
- Q.Are they only black-bodied?
- A.Our breed guide says the name covers the blue-pupil trait itself or black-bodied strains that carry it. Listings may word this differently, so check the body color in the photos and description.
- Q.How large do they grow?
- A.There is little data on the adult size of this variety, and individuals vary. It is a small medaka.
- Q.How long do they live?
- A.There is little documentation on the lifespan of Blue-Eye Medaka, so we can't give a definite figure. Daily care such as water quality, feeding, and temperature management affects their health, so observe them closely as you raise them.
Useful tools for Blue-Eye Medaka care
Learn more about Blue-Eye Medaka in the encyclopedia
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Care difficulty, lifespan, size and diet — all basics covered.
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