How to Successfully Raise Medaka Fry in Indoor Tanks

In this article, I will introduce methods for successfully raising medaka fry in indoor tanks. It is often said that medaka fry do not thrive well in indoor tanks. Until recently, I too experienced continuous failures, with fry decreasing in number. However, I have finally learned how to raise them successfully.

I hope this article will be helpful for beginners and those struggling to raise medaka fry successfully.

Three Tips for Raising Medaka Fry in Indoor Tanks

The tips for raising medaka fry in indoor tanks are as follows:

By following these four tips, I have been able to raise medaka fry indoors just as successfully as outdoors.

Raising Fry Outdoors in Summer is Better

No matter how well you can raise medaka fry indoors, they grow faster during warmer periods when raised outdoors.

In summer, fry raised outdoors in sunlight can become adults in about a month. Outdoors, bacteria and plankton naturally proliferate, and sunlight is 100 times brighter than LED lights, promoting rapid growth.

While outdoor management also requires some attention to direct sunlight exposure, it is generally better to raise medaka fry outdoors from May to September.

Of course, you can also build a greenhouse and use agricultural stoves to raise large numbers of fry year-round.

My Current Indoor Medaka Fry Raising Setup

First, let me introduce my current indoor medaka fry raising setup.

The image above shows the container I use to raise medaka fry. If you look closely, you can see the fry swimming. (The net is for storing eggs)

The medaka fry are growing well in this indoor raising container.

Key Points for Raising Medaka Fry Indoors

Let me explain the key points for raising medaka fry indoors.

Prepare a Container of at Least 10 Liters

The most important thing is to raise medaka fry in a container of at least 10 liters. Many people raise medaka fry in small containers like Tupperware, but in my experience, fry do not thrive in such small containers.

While they may not all die in small containers, the number of fry often gradually decreases, leaving only a few in the end.

The reason for poor growth in small containers could be due to water quality deterioration or starvation. Raising fry in a container of at least 10 liters significantly increases their survival rate.

Of course, if you prepare larger containers as the fry grow, they won’t die, but it’s more convenient to start with a large container. If you are struggling to raise fry in small containers, please try using a larger one.

Feed Plenty of Powdered Food

The main cause of poor growth in medaka fry is starvation. Medaka fry must continuously eat food 24 hours a day to avoid starvation and death. Additionally, feeding plenty of food accelerates their growth. Therefore, providing plenty of food and quickly getting them past the vulnerable fry stage increases their survival rate.

I feed medaka fry food 3 to 4 times a day, with each feeding being about a spoonful of powdered food. Although this may seem like a lot, I believe it is still insufficient.

To prevent water deterioration due to leftover food, I include Ramshorn snails and Neocaridina shrimp for cleaning. These shrimp and snails do not eat medaka fry or eggs.

Additionally, recent foods contain beneficial bacteria and are designed not to pollute the water, so it’s okay to feed a bit more. Medaka fry are very resilient to water quality deterioration, and as long as there is no buildup of leftover food, they will not die from slight water quality changes.

Various companies sell excellent formulated feeds for fry. Even those sold at home improvement stores can sufficiently nourish them. I use the Itosui fry-specific food shown in the image above.

PSB and Infusoria Alone are Not Enough

Until recently, I was also mistaken, but PSB and infusoria alone do not provide sufficient nutrition for fry.

Notably, infusoria are known to be very low in nutritional value, and fry will not grow at all if fed only infusoria, so be careful. Powdered food is the best for fry growth and promotes rapid development. However, medaka fry do not eat leftover powdered food, so relying solely on it can lead to starvation.

PSB and infusoria are necessary to prevent starvation, but it is important to also provide plenty of powdered food.

PSB Helps Prevent Starvation

Therefore, in addition to powdered food, I use PSB. I add about 2cc to 5cc of PSB twice a day. I also add water plants and leaves to the fry raising container to encourage plankton growth. Additionally, adding daphnia can significantly reduce the number of starving fry.

Maintain Temperature with a Heater

Finally, keep the temperature of the medaka fry tank between 23°C and 25°C using a heater. Low temperatures slow fry growth, and no matter how much food they are given, they will not mature. Prolonging the fragile fry stage increases the risk of starvation. Since I started directly heating the water with a heater from autumn to winter, the survival rate of medaka fry has significantly increased.

Prevent Nitrite Buildup

Medaka fry tend to decrease in number if left unattended. The causes can vary, such as starvation or fighting, but harmful substances like nitrite and ammonia might be the main culprits. In small containers without water changes, ammonia and nitrite accumulate, causing the weaker fry to die first. Therefore, regularly changing the water or purifying it with a filter is recommended.

Try Raising Medaka Fry Indoors

Raising medaka fry indoors can be tricky at first, but as long as you use a large container and ensure they have enough food, it usually works well. Please give it a try!

However, in summer, raising medaka fry outdoors is much faster for growth, so if you struggle, it might be better to switch to outdoor raising.

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