Eggs

About Eggs

Medaka eggs have long been a familiar subject of life science education in Japanese homes and schools. Medaka have been kept as ornamental fish since the Edo period, and their ease of breeding has made egg observation and hatching a widespread practice. Freshly laid eggs cling together with adhesive threads, but gradually separate into individual round, transparent spheres. As development progresses, eyes become visible inside the egg, and just before hatching, the fry can be seen moving. At around 25°C, hatching typically occurs within 10 to 14 days. The greatest appeal of raising eggs is witnessing the birth of life from the very beginning. Watching a fry break free from its shell and swim for the first time is a moving experience no matter how many times you see it. Through observation, breeding, and raising fry, a natural appreciation and affection for living creatures grows.

5 things to know before welcoming a Eggs

1. 1Aim for 25–28°C Water Temp

   Water temperature significantly affects egg development, with 25–28°C being the most stable range for hatching. Lower temperatures slow development, while above 30°C increases the risk of deformities or unfertilized eggs. Use a heater and thermometer to maintain consistent conditions.

2. 2Separate Eggs from Adult Fish

   Adult fish and other medaka will readily eat eggs, so it is important to move eggs to a separate container immediately after spawning. Gently remove eggs from the spawning mop and keep them in a small dedicated hatching container. Isolation significantly improves hatch rates.

3. 3Hatching Takes About 10–14 Days

   At 25–28°C, eggs typically hatch within 10 to 14 days of being laid. Cooler water will extend this timeline. Once you can see eyes forming inside the egg, hatching is approaching — a rewarding moment to watch for.

4. 4Prepare Fry Food in Advance

   Newly hatched fry have tiny mouths and cannot eat regular medaka food. Powdered fry-specific food or infusoria such as paramecia should be prepared in advance. Have everything ready a few days before the expected hatch date to avoid scrambling.

5. 5Cost: Eggs Are Budget-Friendly

   Medaka eggs are generally affordable, often sold in lots of 10 to 30 eggs starting at a few hundred yen, making them a lower-cost entry point than buying adults. However, hatch rates and egg quality vary between breeders, so choosing a reputable seller matters. Factor in starter costs for a fry container, food, and water conditioner.

Frequently asked questions about Eggs

Q.Are white or cloudy eggs dead?

A.White or cloudy eggs are usually unfertilized or dead. If mold is present, the egg is definitely dead and should be removed immediately to prevent it from spreading to healthy eggs. Eggs that are clear with visible eyes or blood vessels are a good sign of healthy development.

Q.How many days until eggs hatch?

Useful tools for Eggs care

Eggs related articles

More in this category