Medaka Egg Management and Hatching Guide | Steps from Egg Collection to Fry Birth | ブリちょく
Medaka| ✍️ BreederDirect Editorial
Medaka Egg Management and Hatching Guide | Steps from Egg Collection to Fry Birth
Detailed explanation of the process from medaka spawning to hatching. Covers egg collection timing and methods, egg management, fungal prevention, and post-hatching fry care, all compiled for beginners.
Key Takeaways
Detailed explanation of the process from medaka spawning to hatching. Covers egg collection timing and methods, egg management, fungal prevention, and post-hatching fry care, all compiled for beginners.
Spawning Conditions and Egg Collection Timing
Medaka breeding is attractive because it is relatively accessible even for beginners in fish keeping. However, the hatching rate changes dramatically depending on whether you know the proper egg management method. To avoid wasting eggs that are laid, it is important to master the steps from egg collection through hatching to initial fry care.
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Medaka will begin reproductive behavior when the conditions of water temperature above 20℃ and photoperiod of 13 hours or more are met. In outdoor setups, spawning season is from late April through September. With indoor setups, if you provide heaters and lighting to create the right environment, spawning can occur throughout the year.
Females typically spawn in the early morning, and you can observe them swimming with clusters of eggs dangling from their body. Eggs adhere to aquatic plants or spawning substrates, so collecting eggs daily is ideal. If you leave eggs in the same container as parent fish, they risk being eaten, so move them to a separate container promptly.
Historically, roots of water sprite and palm fiber have been used as spawning substrates, but in recent years commercial sponge-based spawning mats have become the standard. You can complete egg collection simply by moving the spawning mat to a separate container, so there is no need to handle eggs directly by hand, making the process very convenient.
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Egg Management Methods | Water and Temperature Determine Hatching Rate
Collected eggs should be kept in a separate container from parent fish. Small plastic containers or food storage boxes are sufficient.
Why Use Tap Water as Is
For egg management, use tap water without dechlorinating it. This is because the trace chlorine in tap water suppresses fungal growth. The water level should be just enough to submerge the eggs (approximately 5cm depth). Change all the water daily to maintain a clean environment.
Relationship Between Water Temperature and Hatching Duration
The optimal water temperature is 25–28℃. Medaka egg hatching is guided by the principle of "accumulated temperature-days of 250℃," with hatching beginning when the product of water temperature × number of days reaches 250.
Water Temperature
Days to Hatching (approximate)
20℃
~13 days
25℃
~10 days
28℃
~9 days
If water temperature is too low, hatching is significantly delayed, and the risk of fungal infection increases during this period. Maintaining a stable temperature with a heater or room temperature control is fundamental to improving hatching rates.
Distinguishing Fertilized Eggs from Unfertilized Eggs
It is also important to observe eggs daily. Fertilized eggs are transparent, and as days pass, you can see dark eyes and the body developing inside. In contrast, white, cloudy eggs are unfertilized or fungal-infected eggs. Remove them immediately with a dropper or tweezers. If left alone, fungus will spread to the healthy eggs nearby.
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Fungal Prevention and Tips for Improving Hatching Rates
The greatest enemy of eggs is water mold. Fungus from unfertilized eggs spreads to adjacent fertilized eggs, preventing hatching. Combining the following three strategies can dramatically improve hatching rates.
① Early Removal of Unfertilized Eggs
Observe daily and promptly remove white, cloudy eggs. It is important to address fungus before it spreads from a single egg.
② Separating Eggs One by One
Freshly-laid eggs are connected by thread-like filaments. By gently separating them with your fingertip, isolating each egg individually, you can prevent fungus from spreading to adjacent eggs. Medaka eggs are tougher than they look, so they won't break easily when pinched with your fingers. At first, you may hesitate to touch them, but with practice, the process becomes much easier.
③ Utilizing Methylene Blue
Managing eggs in water with a light solution of methylene blue for aquarium use (resulting in a light blue color) can effectively suppress water mold development. Since it is readily available at home centers and aquarium shops, definitely use it if you are serious about breeding.
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Newborn Fry (Needle Fish) Care
Fry that have just hatched are called "needle fish," and they are only about 2mm in body length. How you care for them during this period greatly affects their subsequent survival rate.
No Feeding Required for the First 2–3 Days
Newborn fry have a yolk sac attached to their belly and can survive on its nutrients alone. Feeding is not necessary during this period, and excess food will only foul the water, so avoid feeding. Once the yolk sac is absorbed, feeding can begin.
Selecting Appropriate Food for Fry
Standard adult fish food is too large for needle fish to eat. Use powder-form fry food or crush adult food with your finger into powder form. Feed small amounts divided into 3–4 feedings per day for efficient growth.
Additionally, raising fry in green water (water populated by plant plankton) provides an environment where fry can constantly feed on microscopic food, improving survival rates. Culturing and feeding infusoria (Paramecium) is also effective, and many breeders practice this method because it dramatically increases needle fish survival rates.
Water Change Precautions
There is a risk of sucking in fry when they are small during water changes. Avoid complete water changes and instead remove debris from the bottom gradually with a dropper. Once fry reach approximately 5mm in body length, you can switch to gradual water changes.
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Summary | Taking Your First Step in Breeding with Brichoku
The key points for medaka egg management are: consistent egg collection, fungal prevention with tap water, proper temperature maintenance, and early removal of unfertilized eggs. During the needle fish stage, pay careful attention to feeding and water quality management; once they survive the first two weeks, the fry become significantly hardier.
To succeed in medaka breeding, obtaining quality breeding stock is also essential. On Brichoku, you can purchase breeding pairs or trios (1 male and 2 females) directly from breeders with breeding experience. A major advantage is that you can easily consult with the breeder themselves about breeding tips and selection criteria for each variety.
From egg management to fry rearing, with the support of experienced breeders, we encourage you to experience the true joy of medaka breeding.
