Medaka Egg Management and Fry Rearing | Tips for Raising Hatch Rates
Explains the key points of collecting, managing, and hatching medaka eggs, as well as feeding, water quality management, and growth-stage-specific care methods for fry (newborns).
Key Takeaways
Explains the key points of collecting, managing, and hatching medaka eggs, as well as feeding, water quality management, and growth-stage-specific care methods for fry (newborns).
While medaka breeding is relatively easy, managing eggs and rearing fry require certain techniques. In particular, fry immediately after hatching (newborns) are extremely delicate, and if proper care is neglected, large numbers will die. This article explains in detail the management methods from egg collection through fry reaching a stable size.
Egg Collection Methods
Medaka begin spawning when water temperature reaches 20°C or higher and daylight hours exceed 13 hours. Females lay eggs in the morning, carrying them suspended from their abdomen for a time before attaching them to aquatic plants or spawning substrates.
Types of spawning substrates: Water sprite roots are the natural spawning substrate that medaka prefer most. Artificial spawning substrates (made from palm fiber or sponge) are also convenient and easy to collect. Homemade spawning substrates made by bundling yarn are also effective.
Egg collection: Remove the spawning substrate with the adult fish and transfer it to a separate container. If eggs are attached, they can also be collected by pinching them with your fingers. Medaka eggs are surprisingly hard and will not break even if pinched with fingers. If sticky threads are attached, gently separate them with the pad of your finger and separate the eggs one by one.
Why to separate from adults: Adult fish will eat eggs they have laid or fry that have hatched. Always manage eggs in a separate container.
Egg Management Methods
Container: Shallow plastic containers or tupperware are easy to handle. A water volume of approximately 500ml to 1 liter is sufficient.
Water: The key is to use tap water without dechlorination. Chlorine has antibacterial properties and helps prevent fungal growth (water mold) on eggs. The chlorine in tap water is harmless to eggs, but once hatching approaches, switch to dechlorinated water.
Water temperature and hatch time: Days to hatch can be estimated using the formula "250÷water temperature (°C)". At 25°C water temperature, approximately 10 days; at 30°C, approximately 8 days. Higher water temperatures result in faster hatching, but note that exceeding 30°C increases the rate of deformities.
Daily management: Unfertilized eggs (white, cloudy eggs) should be removed as soon as found. If left unattended, unfertilized eggs develop water mold that spreads to surrounding fertile eggs. Fertile eggs are transparent, and after a few days, eyes become visible inside. Exchange water every 2-3 days to maintain cleanliness.
Methylene blue: Adding a few drops of methylene blue to the water increases fungal prevention. A light blue color concentration is sufficient.
Care of Newborns Immediately After Hatching
Fry immediately after hatching are called "newborns," and are extremely small at approximately 2-3mm in body length.
No feeding for the first 2 days: Newborns have a yolk sac on their abdomen and obtain nutrition from it for approximately 2 days after hatching. Feeding is not necessary during this time.
Initial food: After the yolk sac is absorbed, powdered fry food (crushed to powder consistency) or infusoria are suitable as the first food. Infusoria can be cultured at home using a culture kit and are live food optimal for newborn size. PSB (photosynthetic bacteria) are also popular as initial fry food.
Green water: The most convenient and effective feeding environment for newborns is green water (water rich in phytoplankton). Newborns can feed continuously on plankton in green water, significantly reducing starvation risk. Green water forms naturally when culture water is exposed to sunlight.
Growth-Stage-Specific Care for Fry
Newborn stage (up to 1cm): Minimize water changes. Only remove debris from the bottom with a pipette, avoiding large water changes. No water current, and do not use filters. Use extremely weak aeration or none at all.
Fry stage (1-1.5cm): Providing brine shrimp nauplii results in rapid growth. At this stage, finely granulated artificial fry food can also be consumed. Even fry born at the same time show growth rate differences. Larger individuals may eat smaller ones, so separate containers if size differences appear.
Young fish stage (1.5cm and up): Can be fed crushed regular adult food. Sponge filters can also be used. Once reaching approximately 2cm, the risk of being eaten by adults is significantly reduced.
Handling of Individuals Removed Through Culling
What to do with individuals removed during culling is an issue all breeders face. The following options are available:
- Give to friends and acquaintances: Sharing with acquaintances interested in goldfish is most ideal
- Have pet shops accept them: Some shops accept them for free
- Exchange or transfer through hobby groups: Regional hobby groups sometimes conduct exchanges between members
- Find adoptive homes through SNS and online communities: Recruit adoptive homes in goldfish enthusiast communities
Culling is unavoidable work for raising quality individuals, but remember that removed individuals also have lives, and strive to handle them as responsibly as possible.
Parent Fish for Breeding from BreederDirect
If you want to enjoy medaka breeding, selecting quality parent fish is the starting point. BreederDirect allows you to purchase medaka with well-established breed characteristics directly from breeders. You can consult with breeders about breeding advice and egg management methods, making it safe even for first-time breeders.