Big-Eye Medaka
The Big-Eye Medaka is a selectively bred variety prized for eyes that grow noticeably large relative to its body — a different effect from the bulging eyes of Demekin medaka, since here it's the eye diameter itself that expands. First discovered and fixed as a stable trait by breeder Niiya in 2009, it's a relatively recent addition to the medaka world. Its round, oversized eyes give it an endearing, expressive look that makes it fun to watch swim. Because this variety is considered suited to intermediate keepers, it's best approached once you're comfortable with basic water quality management and daily observation. Adults reach a maximum of about 4cm in standard body length, with the eyes remaining a striking feature relative to that compact frame. The Medaka Improvement Web Encyclopedia currently lists 17 recognized varieties, so individual differences in eye size and body coloration add to the appeal.
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- Body Type
- Scale Type
- Size
- Origin
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Big-Eye Medaka key facts
- Care level
- Intermediate
- Lifespan
- 2-3 years
- Size
- Up to about 4cm SL
- Temperature
- 18〜28℃
- Diet
- Prepared medaka food, green water
- Lighting
- The size of the eye reads from above and from the side, so the fish suits either style of keeping. The Medaka Web Encyclopedia recommends outdoor keeping and suggests shading half the container in summer.
- Diet & Nutrition
- Commercial prepared medaka food is the staple, given in an amount finished within a few minutes. Leftovers decay and foul the water, so adjust the quantity. Green water rich in phytoplankton suits fry rearing.
- Water Temperature & Quality
- Slightly acidic to slightly alkaline water is considered ideal, and the water drifts toward acidic as keeping continues. Around one water change per week is the guideline, and because sudden shifts in temperature or pH cause stress, acclimatise new fish by floating the bag. FishBase records the wild water chemistry of this species as pH 7.0-8.0 and hardness 9-19 dH.
- Tank Mates & Compatibility
- A peaceful schooling fish, normally kept as a group of the same variety. One litre of water per fish is the guideline against overcrowding; overstocking causes poor growth, reduced breeding, oxygen shortage and water fouling.
- Breeding
- Outdoors the spawning season runs from about April to October, once water reaches 18C or above with 12-13 hours of daylight. For year-round indoor breeding, 25-28C water and over 13 hours of lighting are the guideline. Eggs hatch at a cumulative 250 degree-days, about 10 days at 25C.
- Health & Notes
- Fish with larger eyes are rated higher, and selection is made by comparison with normal-eyed siblings. Big-eye has also been combined with other eye traits such as bubble-eye, so check which traits a line carries when acquiring fish.
About Big-Eye Medaka
Big-Eye Medaka is a selectively bred variety with eyes that grow large relative to its body, fixed as a stable trait in 2009. Suited to intermediate keepers, adults reach about 4cm.
7 things to know before welcoming a Big-Eye Medaka
1Appreciating the Big Eyes
Because the Big-Eye Medaka's eyes grow large relative to its body, it can be enjoyed both from above (uwami) and from the side (yokomi), each angle showing a different expression. Adjusting your lighting and keeping the water clear helps highlight the texture of those oversized eyes.
2Basic Water Quality Care
As an intermediate-level variety, it does best when you avoid sudden swings in temperature and pH and keep up with regular water changes. Like other medaka, maintaining clear water through filtration and substrate care also makes it easier to observe.
3Choosing Tankmates
This variety tends to have a calm temperament and generally does well alongside medaka of similar size. Avoid pairing it with much larger or more aggressive fish so it can swim without stress.
4Daily Health Checks
The large eyes make it relatively easy to keep an eye on their condition during daily observation. If you notice sluggish movement or reduced interest in food, check water quality and temperature first.
5Acclimating Before Arrival
When introducing a new fish, take time to acclimate it gradually to reduce stress from temperature and water chemistry differences. Let the transport bag's water temperature match the tank before slowly mixing in the new water.
6Feeding and Water Change Routine
Keep feeding amounts and frequency consistent to prevent leftover food from fouling the water. Regular partial water changes help keep conditions stable for long-term enjoyment.
7Knowing Its Origin
The Big-Eye Medaka is a relatively recent variety, discovered and fixed by breeder Niiya in 2009, with 17 varieties currently listed in the Medaka Improvement Web Encyclopedia. Understanding its background can deepen your appreciation once you bring one home.
Frequently asked questions about Big-Eye Medaka
- Q.How is Big-Eye Medaka different from Demekin (bug-eye) medaka?
- A.Demekin medaka develop eyes that protrude outward from the body, while Big-Eye Medaka instead have an enlarged eye diameter without that outward bulge. The visual effect can look similar at a glance, but the underlying trait is different.
- Q.How difficult is it to keep Big-Eye Medaka?
- A.It's generally considered suited to intermediate keepers. It's best to have some prior experience with basic medaka care and water quality management before taking one on.
- Q.How big does Big-Eye Medaka grow as an adult?
- A.Adults reach a maximum of about 4cm in standard body length. Because the eyes are large relative to the body, the fish can feel more visually striking than its actual size suggests.
- Q.When was the Big-Eye Medaka variety established?
- A.It was discovered and fixed as a stable trait by breeder Niiya in 2009, making it a relatively recent addition among improved medaka varieties. The Medaka Improvement Web Encyclopedia currently lists 17 varieties.
- Q.Is Big-Eye Medaka subject to any regulations?
- A.Big-Eye Medaka is not covered by CITES.
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