I am often asked, "Medaka is producing eggs, what should I do?" If you want to breed medaka, what you must do is eggs isolation.
Medaka lay eggs early in the morning
Medaka spawns in the early morning. Eggs are attached to the female belly for a while, but usually lay out eggs to aquatic plants in the morning.
It is important to transfer the eggs to a separate container, as the Medaka parents will eat fry, but veterans take eggs directly from the parent's belly. However, because the burden on parents is large, let's wait to lay it on aquatic plants etc. and collect eggs.
Let's transfer the eggs to another container
Medaka eats her own child. There is not much to eat eggs, but as soon as it hatches, it will be mistaken for food and eat.
If you want to breed medaka, transfer it to another container when you find medaka eggs. Let's use another container for breeding. Because moving the fry is burdensome for fry, let the container to be hatched be something that can be used for breeding fry.
The water in the container that holds the eggs may be tap water. Rather, tap water has a bactericidal effect and cleans the eggs.
Remove white eggs
The fertilized eggs of medaka are colorless and transparent, or slightly yellowish. Eggs that become white and turbid are unfertilized and do not hatch, and rot and mold grow.
Let's remove the egg which has become white. You can prevent mold from sticking to other fertilized eggs.
If you are not sure if it is a fertilized or unfertilized egg, try pinching the egg with your finger. Fertilized eggs are elastic and can not be crushed, but unfertilized eggs are easily crushed.
Time to hatch
Medaka eggs hatch at 250-degree-day. The 250-degree-day is the average water temperature multiplied by the number of days, and if the average water temperature per day is 25 degrees, it is calculated to hatch in 10 days.
It will be from the third day after hatching that fry medaka will start feeding, so check whether eggs are hatched daily.
Column ~ To increase the egg hatching rate ~
Medaka eggs often die when the water temperature is low. In nature and outdoor breeding, medaka spawns from around April. This means that the eggs are produced after the water temperature is high.
In order to ensure that the eggs hatch, the water temperature must be maintained at 15°C or higher. In order to ensure that eggs born in April can be hatched outdoors, it is better to install a small plastic house on the water tank to prevent the water temperature drop at night or early morning.
In addition, medaka can not be reared with tap water, but the eggs are not affected by chlorine, so to prevent mold, until the eyes of medaka are clearly visible in the eggs, changing water by tap water is also effective.
However, since the fry fish hatched from eggs will soon die in tap water with chlorine remaining, it is necessary to make sure that chlorine is completely removed by the time eggs are hatched.
Blog Source: https://www.medakanoouchi.com/howto/egg.html.en