For those who have started raising Japanese Medaka but don't know what to do...
Let us guide you how to raise Medaka!
We will explain to you everything you need to know about Medaka, such as “what you need for breeding”, “how to change water”, “types and frequency of feeding ”, and how to breed!
Contents（Click or tap to move to the relevant content）
・Aquarium
・How to choose bottom gravel
・Water plants
・Place to breed
・Breeding water
・Types of food and how to feed them
・How to change water
・Frequency and method of changing water
・About Green Water
・How to recognise the difference between male and females
・About the time of spawning
・Success of spawning
・How to observe spawning
・Hatching conditions
・How to raise new born fish
・Various diseases of Medaka
The best and recommended amount for aquarium is 1L of water per fish.
Medaka are strong fish, so any containers which keep water safe without leakage will be good. Glass aquariums, Styrofoam, garden planters, and plastic containers are usually sold at pet shops.
The important thing to remember is that finding the right aquarium for the size of Medaka. Figure out the amount of water that goes into the aquarium first, then keep one fish per liter as a guide.
For example, if you want to raise 10 Medakas, you will need at least 10 litters of water to avoid overcrowding in the aquarium.
If you overcrowd it, they will slow down their growth, prevent eggs from being laid, and lack of oxygen in the water will occur.
It can also cause them to become sick and weaken. If the aquarium is too big for your Medaka amount then maintenance will become difficult so keep it simple and follow the guidance.
That way, you will be able to perform daily maintenance without any problems.
＜Aquarium example＞
There are 12L and 8L sized aquariums to choose from depending on the number of fish you want to look after and the size of the area where they will be placed.
●black styrofoam box
This aquarium is suitable for outdoor top viewing. These containers are strong, sturdy and easy to use so are highly recommended for breeding! Some people use them for shipping Medaka.
●glass aquarium
This aquarium is suitable for indoor viewing.
Rounded gravel is recommended
By adding bottom sand to your aquarium, it can help to give the tank a clean appearance and provide a habitat for bacteria that can encourage water deterioration. Bacteria that grows in the bottom gravel decompose highly toxic ammonia from food scraps and Medaka excrement will convert it into almost harmless nitrate. In other words, bacteria are essential micro-organisms for water stability and purification.
When choosing bottom gravel, use rounded sand with no corners if possible. When startled, Medaka will try to burrow into the ground, which can cause injury if the gravel is angular. There are also red ball soil and Medaka soil are available ,so please choose it to your preferebces.
There is also a breeding method called “Bare tank” that does not require bottom sand layer. Bare tank has the advantages of making it easier to remove decaying matter from the bottom and to find eggs that have been laid. This is a breeding method recommended for those who can change the water frequently and those who wish to collect as many eggs as possible.
Warter plants are recommended for spawning and summer shade
Water plants can provide hiding places and spawning grounds for Medaka. It also provides oxygen through photosynthesis during a day and purifies the water. So including as many aquatic plants as possible is better for Medaka.
Water hyacinth and anacaris are often used in keeping Medaka. The roots of water hyacinth absorb excess nutrients in the water, purify it, provide shade in summer and prevent water temperature from rising.
They are also ideal as egg-laying sites for Medaka, and are used by many people for egg collection during the summer. However, if the roots grow too long, they may get entangled with the Medaka and make it difficult to get out, so it is important to cut them when they have grown to a certain extent.
If there are too many water hyacinth, the amount of carbon dioxide increases at night and it can cause Medaka to run out of oxygen to kill them. Be careful not to add too much water hyacinth in the aquarium.
Anacaris is easy to grow, inexpensive and easy to purchase, and is used by many people. It is a common aquatic plant which found in ponds and rivers. So why don’t you try collecting them and using them. Once thing to remember though, naturally growing plants may contain with parasites or bacteria, so they should be sterilised before being added to the aquarium. Also, the same problem may occur with purchased water plants, so wash them thoroughly before use.
Place the aquarium outside in a sunny place.
Place the aquarium in the sunniest location. Sunlight has a bactericidal effect, which helps to keep Medaka in the aquarium strong and healthy, making them less susceptible to diseases. It is also good for increasing fertility and for colour frying. From this point of view, the ideal place to raise Medaka is outdoors.
However, it should be noted that the water temperature can become quite high in the summer if they are continuously exposed to sunlight. In particular, it is recommended to choose a place where the aquarium is not exposed to the Western sun as it makes the water temperature even hotter than it is during a day.
If you must keep your aquarium in a location where the sun shines from the west, use a reed screen to create shade so that the water temperature doesn’t exceed 30℃.
Keeping Medaka indoor is attractive as it allows you to admire Medaka any time. However, it inevitably leads to a lack of light. That means it can lead to vitamin D deficiency, which makes Medaka more susceptible to diseases.
If Medaka is kept indoors, aquarium light should be used to provide additional light. It is advised to keep the light on for12 to 14 hours. Even if the fish are kept near a sunny window, where the daylight hours are almost the same as outdoors, we recommend to keep the light on if the fish are kept indoors.
Ensure that breeding water is calcified.
One of the most important aspects of keeping Medaka is water.
Medaka no yakata uses pumped up groundwater but we believe that most enthusiasts use tap water. The thing you need to watch out for is chlorine.
Chlorine is used in tap water to disinfect it. The chlorine in tap water can be harmful to Medaka, To remove chlorine from tap water, leave the water outside for about 24 hours or inddors for two to three days. It will naturally remove the chlorine from the water. Also, if you keep the water constantly drawn up, the water temperature will be the same as the air temperature which makes convenient to use it for changing water .
If and when you need to use a tap water, use some commercial removed chlorine water. Tap water or ground water used for breeding may have pH problems in some areas. So, it is best to check the pH beforehand using a commercially available test that measures pH and other parameters.
pH indicates the degree of ionic concentration in the water. pH=7 is neutral so if it is below this value, the water is acidic and above means alkaline. Ideally Medaka should be kept in a slightly acidic to slightly alkaline range. pH varies depending on the rearing environment. Breeding water becomes more acidic as it is. A too low pH can be harmful to Medaka.
Transferring Medaka to water with a difference in pH or water temperature may cause them to become ill because of the sudden changes in water quality. Therefore, when purchasing Medaka or removing them to a different tank when you need to change water, ensure that the water is well matched.
When adjusting the water, put the Medaka in a small container along with the breeding water and let it float for a while in the new aquarium. The water temperature will be the same after about an hour, so add water from the new environment little by little and slowly get used to the new environment. This will prevent sudden changes in water quality and temperature.
＜TIPS＞
When replacing the aquarium and changing the water, it is recommended to pump up new water into the aquarium which containing Medaka. That way the water temperature is the same and there is less strain on the aquarium. It is best to prepare the water a day before for outdoor aquariums and two to three days before for indoor aquariums to shift chalky water.
Adding the original breeding water at the same time will reduce the change in water quality and less stressful to Medaka.
The best feeding amount is food which can be eaten in three minutes.
Medaka are accustomed to people and will approach humans vigorously when approached. This shows that the keeper is feeding them properly. Medaka are omnivores and will eat a variety of things, including plankton, daphnia, daphnids, borers, plants, small insects and even the eggs and fry they have laid.
If you are keeping Medaka in a limited space at home, make sure to feed them with commercially available Medaka food, as naturally occurring feeds are not nutritious enough. (see below list of our Medaka food you can purchase in the shop)
Medaka have their mouth pointing upwards, so they eat food which is floating on the surface of the water. On the other hand, when they eat food at the bottom of the water, they have to stand on their heads. It is advisable to choose a food which can float well.
Most commercially available Medaka food are highly emergent so choosing food which specifically for Medaka is the safest. Reducing the amount of leftover to absolute minimum will ultimately help to prevent water quality.
When you feed Medaka, the amount we should be giving are something which can be eaten in three to five minutes. The more food leftover in the water, the quicker the water quality will deteriorate. The amount of food will be depend on the activity of Medaka and number of Medaka in the aquarium so it is important to adjust the amount of food by observing Medaka closely.
During high temperature periods like summer, when the water temperature rises, Medaka become very active and need to be fed at least twice a day.
On the other hand, during low temperature periods like winter, when the water temperature drops below15°C (59°F) it is fine to feed them once a day.
When feeding Medaka, we need to watch out not to overfeed it. Overfeeding can lead to deterioration of water quality as uneaten food decomposes.
Quality of water is life to Medaka so deterioration of water quality can lead to death in the worst scenario. Medaka have no organs that can be called stomach and don’t have ability to store a lot of food. For those reasons, the best way to feed Medaka is to feed them as often and little as possible in small amount.
When keeping Medaka outside, where the water temperature becomes cooler, they become less active. When the water temperature drops below 15℃ and outside temperature drops below 10℃ in the winter, they are close to hibernation and don’t need to be fed. If Medaka stop coming to the surface after feeding, it is a sign to stop giving them more food.
Apart from commercial Medaka food, they eat live food such as daphnia, threadworms, red worms and brine shrimp. These live food are more hands-on and more expensive than artificial food( power food), but they are highly nutritious and very effective for growing Medaka. It has been said that Medaka can live on artificial food alone so live food is recommended for those who want to breed and grow them faster.
＜Bait sold at our store＞
●Hikari plankton
This product has been tested in our shop properly. It has also been confirmed to be reliable food without any issues or disease and growth rate.
●High quality feed for raising young fish (powder type)
For prevention and improvement of diseases! This is an improved immunity food which helps their growth!
This food is designed to prevent disease and also adds growth potential. The particles are very fine like a powder and they won't polute the water. They make the best food for development of baby fish.
At the Medaka no yakata, all of our baby fish and intermediate fish are currently fed this food! It also has excellent floatability.
●Food for spawning and breeding
This food Hikari Bacteria is fortified with highly unsaturated fatty acids and phospholipids to take it into account the number of Medaka eggs laid and the hatching rate of eggs.
The high protein, high fat and high calorie formula is designed to nurture female Medaka that lay eggs every day and the live bacillus helps to maintain the intestinal balance of Medaka.
The food grains are also broken down into easily digestible and absorbable pieces. This enables the Medaka to fully absorb and utilise the nutrients necessary for its growth (from Kyorin HP).
Deterioration of water quality is a source of disease.
Water is life for Medaka. Therefore, deterioration of water quality is a major factor in Medaka becoming ill or dying. Before this happens, make sure to regularly change and keep good quality of water.
No.1 cause of water pollution is Medaka faeces and food scraps. These gradually turn into toxic substance ammonia in the water and they will accumulate.
This is where micro-organisms such as bacteria in the water come into play. Bacteria which lives in the bottom of sand filter media and sponges. This bacteria works to break down ammonia.
However, bacteria takes some time to reproduce so we need to keep our eyes on the early stages of setting up a new aquarium. Water that looks clear and transparent may in fact contains build-up ammonia.
So, give just enough amount to avoid uneaten food.
As mentioned above, bacteria break down ammonia into almost harmless nitrates. They are harmless in small quantities but as they accumulate and become harmful to Medaka.
If there are water plants in the water, they are partly absorbed as nutrients but they also need to be discharged when changing water. This means that regular changing of water is necessary even when bacteria are fully reproducing.
Changing the water once a week is a must!
The frequency and timing of changing water will depend on the number of Medaka ,the size of the aquarium, the growth of bacteria and other micro -organisms. However general guide says half of the water should be changed once a week as it is all depends on the season and other facts.
This is only a rough guide so daily observation and flexible response are necessary. If you feel that your Medaka don’t look well even it is less than a week from changing water, follow your gut feeling.
If you change the aquarium water completely, Medaka may be overloaded and weakened. To minimise changes in quality of water, leave about half of the original breeding water in the aquarium. That will reduce the strain on Medaka and allow to change water safely.
When and if the breeding water is cloudy white or the green water becomes reddish brown, the water isn’t great and you need to replace your aquarium water completely without using original breeding water.
If bottom sand is laid, it should be washed thoroughly as decaying food could cause poor water quality. If the soil is laid down, it should be cleaned gently as strong pressure can cause it to loose its shape. Soil has a life span of about one year so if you feel that it is no longer effective, replace it with new soil straightaway.
If you think your Medaka don’t look well when you feed them, make sure to change the water at least once a week and remove any faeces or leftover food from bottom of the tank. That way, you can keep your Medaka happy and with good health.
Medaka are temperature-changing animals so their activity levels are depending on the water temperature. During hot summer, Medaka are more active and the water tends to deteriorate so it might not depend the size of aquarium or enough to change the water once a week.
As it has mentioned before, Medaka rarely move and they won’t eat if the water temperature falls below 15℃. They also excrete less. Therefore, during the winter, it isn’t necessary to change the water once you remove decaying food waste from the bottom of the water before their hibernation, especially when the water temperature is lower than 10 ℃
＜TIPS＞
Picture below shows changing water with a water pump. It is more effective to stabilise quality of water by cleaning up faeces and leftover food together with changing water. In a bare aquarium, it is easy to check for accumulated decaying but if it is covered with bottom sand, scoop Medaka up first and mix the bottom Sand well afterwards. It will eventually float away. The bottom sand require regular check up and wash.
Green water for training baby fish.
Green water appears when water is with full of phytoplankton. This green water can help the growth of Medaka and it is particularly effective for training baby fish. Baby Medaka are only 4-5mm in size and have small mouths so they can only eat fine food. Phytoplankton is a size that even baby fish are able to eat so it good to remember as one of the food which baby fish can have.
However phytoplankton on its own is not enough to feed them so it is important to add commercially available food. Also if green water gets very dark, that means quality of the water is deteriorating so changing water are necessary.
If you cant see the outline of Medaka at the bottom means quality of the water is becoming thicker so observe and try to maintain the correct thickness.
The way to make green water is to fill up a container with water and leave it outside in the well-lit area where it will naturally make it into green water. However this method takes a lot of time so if you want to make green water quickly, you can add some breeding water that became green as seed water.
The very first step in breeding is to identify between males and females.
One of the great pleasure of keeping Medaka is the breeding of it. Medaka can easily lay eggs and reproduce if the water and living conditions are right. To enjoy Medaka breeding the first step is to learn the difference between male and female MEdaka . Also to be able to distinguish between the two.
You can distinguish between male and female Medaka by the shape of their tail and dorsal fins. The male tail fin is larger than the female one and has a parallelogram like shape. On the other hand, female tail fins are smaller than male ones and are narrower towards the rear( side of caudal).
If you can’t tell and difficult to make a decision by looking at the tail fins, look at the dorsal fins. Male dorsal fins have an incision at the base. Female dorsal fins don’t have an incision.
There are many varieties of improved Medaka with altered body and fin shapes that make it difficult to distinguish between male and female Medaka but all improved Medaka can be judged by looking at their fins. So it is sufficient to remember the aforementioned characteristics of the shirivirgin and dorsal fins.
Spawning season is when the water temperature is above 18 ℃and they need 12 to 14 hours sunlight.
Water temperature and daylight hours play a major role in Medaka spawning. They spawn in an environment with the water temperature of 18℃ or over and 12 to 14 hours of sunlight. Even in cold weather, Medaka will spawn if the above environment is created indoors using a heater or similar. In this case, the water temperature should be set at 25 to 28℃ and the light should be kept on for at least 13 hours.
＜TIPS＞
The photo below shows how they are bred indoors. Water temperature is important, but so is lighting. If you are indoors, turning on the lights regardless of the season will help your Medaka grow healthily. Lighting is even more necessary when collecting eggs.
Spawning pars is female > male.
Medaka have compatibility and if it doesn’t match, they will not lay eggs at all. Conversely if the chemistry is good, even a mating of one male and one female could lay eggs every day. For efficient breeding, it is recommended to have a total of 5 to 10 males and females.
Ideally, the male and female ration should be more female than male. If there are two males then three females, if four males then six females to make it work.
Medaka spawn in an environment with a water temperature of at least 18℃ and 12-13 hours of sunlight. Food is also very important for spawning and if Medaka are not well fed, they will not spawn or the number orf eggs laid will decrease. Therefore daily feeding is very important.
If the aquarium contains water plants or egg lying tools then the eggs are deposited on them.
If the eggs are left untouched, they will be eaten or if they hatch, baby fish will be eaten by the parent Medaka so it is advisable to transfer the eggs laid on the water plants or spawning beds to a separate container with some water plants.
Among water plants, the Photinia layer is a common egg laying plant but as it isn’t possible to purchase all year around, we recommend the special Medaka spawning bed from pet shops.
A surprisingly large number of eggs fall to the bottom of the aquarium without attaching. It’s a good idea to pick up the eggs one by one but you can scoop them up when you are changing the water using a net.
You can also transfer the parent Medaka to another aquarium and leave the eggs in the aquarium to hatch. Try a method of collecting eggs which suits you.
The best time to observe spawning is before sunrise
Spawning in Medaka starts before dawn and it is over before sunrise. If you want to observe the spawning, cover the aquarium with a black cloth during the night to make it pitch-dark and create midnight conditions. When the black cloth is removed following morning, courtship behaviour may start and spawning could take place.
The best hatching condition is 250°C/day
Water temperature plays a major role in the number of days it takes eggs to hatch. If the water temperature is higher then the quicker the eggs hatch. The water temperature is law then it takes them longer to hatch.
There is a method called integrated temperature that calculates the approximate number of days that takes for the eggs to hatch.
It tells 250°C days (water temperature (°C) x number of days (days) = 250°C days) for Medaka. So, if the water temperature is 25℃, it takes about 10 days to hatch and if the water temperature is 20℃ then it takes 12-13 days.
Not all eggs laied by Medaka hatch. There are two types of eggs laid which are unfertilised and fertilised. Unfertilised eggs are soft so they crumble when we push a little.
Fertilised eggs are pale yellow in colour and are so hard that they can’t be easily crushed by pinching them hard with fingers. If unfertilised eggs are left as they are, they gradually turn white and become mouldy in the end. If the unfertilised and fertilised eggs are attached to each other, the mould from unfertilised eggs will also invade fertilised eggs. They will become mouldy eventually. If you find unfertilised eggs, it is best to remove it as much as possible so that more fertilised eggs can hatch instead.
＜TIPS＞
The photo below shows newly hatched baby fish. It is recommended to incubate them at 22-26 °C as if they are kept at above 30°C, they will take less days to hatch but they tend to have less colourations.
The photograph below shows baby fish which hatched a few days ago. They are about 4-5mm in body size and can only eat small food. In addition to powered food, feeding them with phylum Pogonophora will speed up their growth and increase their chance to become adults.
Feed baby fish in small amount few times a day.
A very small creature like the tip of a needle swims in the tank are baby Medaka in the aquarium.
Baby fish can survive without food for 3~4 days after birth as they have a yoke sac in their abdomen. Feed them when the yoke sack is gone.
Feed artificial food for baby fish. It is recommended to use as fine grain powdered fine as possible. Feeding is very important as insufficient food can hinder growth so make sure to feed them well.
However you also need to watch out for uneaten food so it is ideal and best to feed small amount preferably few times a day.
Various diseases of Medaka
Diseases which Medaka can get are “white spot disease”,” water mould disease” and “tail fungus disease”. “White spot disease” causes white spots to appear on the body. “water mould disease” causes white lines of mould on the head, mouth parts and fins. Tailstock disease causes withering and melting of the fins. In both cases, treatment is possible in the early stages. Treatment is more difficult in more advanced and severe cases.
Treatment is either with over the counter fish disease medications or just some salt. Salt has to be made to a salinity of 0.3-0.5 % and the sick Medaka is placed in a salt bath. The water temperature should be raised to about 28 °C as disease causing bacteria are less active at high temperatures.
The best way to keep Medaka healthy is to keep them disease free. To keep them healthy by not overcrowding them in the aquarium, changing the water once a week and feed them enough quantity not too much.
Medaka are strong fish, so any containers which keep water safe without leakage will be good. Glass aquariums, Styrofoam, garden planters, and plastic containers are usually sold at pet shops.
The important thing to remember is that finding the right aquarium for the size of Medaka. Figure out the amount of water that goes into the aquarium first, then keep one fish per liter as a guide.
For example, if you want to raise 10 Medakas, you will need at least 10 litters of water to avoid overcrowding in the aquarium.
If you overcrowd it, they will slow down their growth, prevent eggs from being laid, and lack of oxygen in the water will occur.
It can also cause them to become sick and weaken. If the aquarium is too big for your Medaka amount then maintenance will become difficult so keep it simple and follow the guidance.
That way, you will be able to perform daily maintenance without any problems.
＜Aquarium example＞
●12L water tank
This aquarium is suitable for outdoor top viewing of Medaka. This is an affordable and pretty sized aquarium. It is available in Brown, Black or White.There are 12L and 8L sized aquariums to choose from depending on the number of fish you want to look after and the size of the area where they will be placed.
●８L water tank
●black styrofoam box
This aquarium is suitable for outdoor top viewing. These containers are strong, sturdy and easy to use so are highly recommended for breeding! Some people use them for shipping Medaka.
●glass aquarium
This aquarium is suitable for indoor viewing.
Rounded gravel is recommended
By adding bottom sand to your aquarium, it can help to give the tank a clean appearance and provide a habitat for bacteria that can encourage water deterioration. Bacteria that grows in the bottom gravel decompose highly toxic ammonia from food scraps and Medaka excrement will convert it into almost harmless nitrate. In other words, bacteria are essential micro-organisms for water stability and purification.
When choosing bottom gravel, use rounded sand with no corners if possible. When startled, Medaka will try to burrow into the ground, which can cause injury if the gravel is angular. There are also red ball soil and Medaka soil are available ,so please choose it to your preferebces.
There is also a breeding method called “Bare tank” that does not require bottom sand layer. Bare tank has the advantages of making it easier to remove decaying matter from the bottom and to find eggs that have been laid. This is a breeding method recommended for those who can change the water frequently and those who wish to collect as many eggs as possible.
Warter plants are recommended for spawning and summer shade
Water plants can provide hiding places and spawning grounds for Medaka. It also provides oxygen through photosynthesis during a day and purifies the water. So including as many aquatic plants as possible is better for Medaka.
Water hyacinth and anacaris are often used in keeping Medaka. The roots of water hyacinth absorb excess nutrients in the water, purify it, provide shade in summer and prevent water temperature from rising.
They are also ideal as egg-laying sites for Medaka, and are used by many people for egg collection during the summer. However, if the roots grow too long, they may get entangled with the Medaka and make it difficult to get out, so it is important to cut them when they have grown to a certain extent.
If there are too many water hyacinth, the amount of carbon dioxide increases at night and it can cause Medaka to run out of oxygen to kill them. Be careful not to add too much water hyacinth in the aquarium.
Anacaris is easy to grow, inexpensive and easy to purchase, and is used by many people. It is a common aquatic plant which found in ponds and rivers. So why don’t you try collecting them and using them. Once thing to remember though, naturally growing plants may contain with parasites or bacteria, so they should be sterilised before being added to the aquarium. Also, the same problem may occur with purchased water plants, so wash them thoroughly before use.
Place the aquarium outside in a sunny place.
Place the aquarium in the sunniest location. Sunlight has a bactericidal effect, which helps to keep Medaka in the aquarium strong and healthy, making them less susceptible to diseases. It is also good for increasing fertility and for colour frying. From this point of view, the ideal place to raise Medaka is outdoors.
However, it should be noted that the water temperature can become quite high in the summer if they are continuously exposed to sunlight. In particular, it is recommended to choose a place where the aquarium is not exposed to the Western sun as it makes the water temperature even hotter than it is during a day.
If you must keep your aquarium in a location where the sun shines from the west, use a reed screen to create shade so that the water temperature doesn’t exceed 30℃.
Keeping Medaka indoor is attractive as it allows you to admire Medaka any time. However, it inevitably leads to a lack of light. That means it can lead to vitamin D deficiency, which makes Medaka more susceptible to diseases.
If Medaka is kept indoors, aquarium light should be used to provide additional light. It is advised to keep the light on for12 to 14 hours. Even if the fish are kept near a sunny window, where the daylight hours are almost the same as outdoors, we recommend to keep the light on if the fish are kept indoors.
Ensure that breeding water is calcified.
One of the most important aspects of keeping Medaka is water.
Medaka no yakata uses pumped up groundwater but we believe that most enthusiasts use tap water. The thing you need to watch out for is chlorine.
Chlorine is used in tap water to disinfect it. The chlorine in tap water can be harmful to Medaka, To remove chlorine from tap water, leave the water outside for about 24 hours or inddors for two to three days. It will naturally remove the chlorine from the water. Also, if you keep the water constantly drawn up, the water temperature will be the same as the air temperature which makes convenient to use it for changing water .
If and when you need to use a tap water, use some commercial removed chlorine water. Tap water or ground water used for breeding may have pH problems in some areas. So, it is best to check the pH beforehand using a commercially available test that measures pH and other parameters.
pH indicates the degree of ionic concentration in the water. pH=7 is neutral so if it is below this value, the water is acidic and above means alkaline. Ideally Medaka should be kept in a slightly acidic to slightly alkaline range. pH varies depending on the rearing environment. Breeding water becomes more acidic as it is. A too low pH can be harmful to Medaka.
Transferring Medaka to water with a difference in pH or water temperature may cause them to become ill because of the sudden changes in water quality. Therefore, when purchasing Medaka or removing them to a different tank when you need to change water, ensure that the water is well matched.
When adjusting the water, put the Medaka in a small container along with the breeding water and let it float for a while in the new aquarium. The water temperature will be the same after about an hour, so add water from the new environment little by little and slowly get used to the new environment. This will prevent sudden changes in water quality and temperature.
＜TIPS＞
When replacing the aquarium and changing the water, it is recommended to pump up new water into the aquarium which containing Medaka. That way the water temperature is the same and there is less strain on the aquarium. It is best to prepare the water a day before for outdoor aquariums and two to three days before for indoor aquariums to shift chalky water.
Adding the original breeding water at the same time will reduce the change in water quality and less stressful to Medaka.
The best feeding amount is food which can be eaten in three minutes.
Medaka are accustomed to people and will approach humans vigorously when approached. This shows that the keeper is feeding them properly. Medaka are omnivores and will eat a variety of things, including plankton, daphnia, daphnids, borers, plants, small insects and even the eggs and fry they have laid.
If you are keeping Medaka in a limited space at home, make sure to feed them with commercially available Medaka food, as naturally occurring feeds are not nutritious enough. (see below list of our Medaka food you can purchase in the shop)
Medaka have their mouth pointing upwards, so they eat food which is floating on the surface of the water. On the other hand, when they eat food at the bottom of the water, they have to stand on their heads. It is advisable to choose a food which can float well.
Most commercially available Medaka food are highly emergent so choosing food which specifically for Medaka is the safest. Reducing the amount of leftover to absolute minimum will ultimately help to prevent water quality.
When you feed Medaka, the amount we should be giving are something which can be eaten in three to five minutes. The more food leftover in the water, the quicker the water quality will deteriorate. The amount of food will be depend on the activity of Medaka and number of Medaka in the aquarium so it is important to adjust the amount of food by observing Medaka closely.
During high temperature periods like summer, when the water temperature rises, Medaka become very active and need to be fed at least twice a day.
On the other hand, during low temperature periods like winter, when the water temperature drops below15°C (59°F) it is fine to feed them once a day.
When feeding Medaka, we need to watch out not to overfeed it. Overfeeding can lead to deterioration of water quality as uneaten food decomposes.
Quality of water is life to Medaka so deterioration of water quality can lead to death in the worst scenario. Medaka have no organs that can be called stomach and don’t have ability to store a lot of food. For those reasons, the best way to feed Medaka is to feed them as often and little as possible in small amount.
When keeping Medaka outside, where the water temperature becomes cooler, they become less active. When the water temperature drops below 15℃ and outside temperature drops below 10℃ in the winter, they are close to hibernation and don’t need to be fed. If Medaka stop coming to the surface after feeding, it is a sign to stop giving them more food.
Apart from commercial Medaka food, they eat live food such as daphnia, threadworms, red worms and brine shrimp. These live food are more hands-on and more expensive than artificial food( power food), but they are highly nutritious and very effective for growing Medaka. It has been said that Medaka can live on artificial food alone so live food is recommended for those who want to breed and grow them faster.
＜Bait sold at our store＞
●Hikari plankton
This product has been tested in our shop properly. It has also been confirmed to be reliable food without any issues or disease and growth rate.
●High quality feed for raising young fish (powder type)
For prevention and improvement of diseases! This is an improved immunity food which helps their growth!
This food is designed to prevent disease and also adds growth potential. The particles are very fine like a powder and they won't polute the water. They make the best food for development of baby fish.
At the Medaka no yakata, all of our baby fish and intermediate fish are currently fed this food! It also has excellent floatability.
●Food for spawning and breeding
This food Hikari Bacteria is fortified with highly unsaturated fatty acids and phospholipids to take it into account the number of Medaka eggs laid and the hatching rate of eggs.
The high protein, high fat and high calorie formula is designed to nurture female Medaka that lay eggs every day and the live bacillus helps to maintain the intestinal balance of Medaka.
The food grains are also broken down into easily digestible and absorbable pieces. This enables the Medaka to fully absorb and utilise the nutrients necessary for its growth (from Kyorin HP).
Deterioration of water quality is a source of disease. Water is life for Medaka. Therefore, deterioration of water quality is a major factor in Medaka becoming ill or dying. Before this happens, make sure to regularly change and keep good quality of water.
No.1 cause of water pollution is Medaka faeces and food scraps. These gradually turn into toxic substance ammonia in the water and they will accumulate.
This is where micro-organisms such as bacteria in the water come into play. Bacteria which lives in the bottom of sand filter media and sponges. This bacteria works to break down ammonia.
However, bacteria takes some time to reproduce so we need to keep our eyes on the early stages of setting up a new aquarium. Water that looks clear and transparent may in fact contains build-up ammonia.
So, give just enough amount to avoid uneaten food.
As mentioned above, bacteria break down ammonia into almost harmless nitrates. They are harmless in small quantities but as they accumulate and become harmful to Medaka.
If there are water plants in the water, they are partly absorbed as nutrients but they also need to be discharged when changing water. This means that regular changing of water is necessary even when bacteria are fully reproducing.
Changing the water once a week is a must!
The frequency and timing of changing water will depend on the number of Medaka ,the size of the aquarium, the growth of bacteria and other micro -organisms. However general guide says half of the water should be changed once a week as it is all depends on the season and other facts.
This is only a rough guide so daily observation and flexible response are necessary. If you feel that your Medaka don’t look well even it is less than a week from changing water, follow your gut feeling.
If you change the aquarium water completely, Medaka may be overloaded and weakened. To minimise changes in quality of water, leave about half of the original breeding water in the aquarium. That will reduce the strain on Medaka and allow to change water safely.
When and if the breeding water is cloudy white or the green water becomes reddish brown, the water isn’t great and you need to replace your aquarium water completely without using original breeding water.
If bottom sand is laid, it should be washed thoroughly as decaying food could cause poor water quality. If the soil is laid down, it should be cleaned gently as strong pressure can cause it to loose its shape. Soil has a life span of about one year so if you feel that it is no longer effective, replace it with new soil straightaway.
If you think your Medaka don’t look well when you feed them, make sure to change the water at least once a week and remove any faeces or leftover food from bottom of the tank. That way, you can keep your Medaka happy and with good health.
Medaka are temperature-changing animals so their activity levels are depending on the water temperature. During hot summer, Medaka are more active and the water tends to deteriorate so it might not depend the size of aquarium or enough to change the water once a week.
As it has mentioned before, Medaka rarely move and they won’t eat if the water temperature falls below 15℃. They also excrete less. Therefore, during the winter, it isn’t necessary to change the water once you remove decaying food waste from the bottom of the water before their hibernation, especially when the water temperature is lower than 10 ℃
＜TIPS＞
Picture below shows changing water with a water pump. It is more effective to stabilise quality of water by cleaning up faeces and leftover food together with changing water. In a bare aquarium, it is easy to check for accumulated decaying but if it is covered with bottom sand, scoop Medaka up first and mix the bottom Sand well afterwards. It will eventually float away. The bottom sand require regular check up and wash.
Green water for training baby fish.
Green water appears when water is with full of phytoplankton. This green water can help the growth of Medaka and it is particularly effective for training baby fish. Baby Medaka are only 4-5mm in size and have small mouths so they can only eat fine food. Phytoplankton is a size that even baby fish are able to eat so it good to remember as one of the food which baby fish can have.
However phytoplankton on its own is not enough to feed them so it is important to add commercially available food. Also if green water gets very dark, that means quality of the water is deteriorating so changing water are necessary.
If you cant see the outline of Medaka at the bottom means quality of the water is becoming thicker so observe and try to maintain the correct thickness.
The way to make green water is to fill up a container with water and leave it outside in the well-lit area where it will naturally make it into green water. However this method takes a lot of time so if you want to make green water quickly, you can add some breeding water that became green as seed water.
The very first step in breeding is to identify between males and females.One of the great pleasure of keeping Medaka is the breeding of it. Medaka can easily lay eggs and reproduce if the water and living conditions are right. To enjoy Medaka breeding the first step is to learn the difference between male and female MEdaka . Also to be able to distinguish between the two.
You can distinguish between male and female Medaka by the shape of their tail and dorsal fins. The male tail fin is larger than the female one and has a parallelogram like shape. On the other hand, female tail fins are smaller than male ones and are narrower towards the rear( side of caudal).
If you can’t tell and difficult to make a decision by looking at the tail fins, look at the dorsal fins. Male dorsal fins have an incision at the base. Female dorsal fins don’t have an incision.
There are many varieties of improved Medaka with altered body and fin shapes that make it difficult to distinguish between male and female Medaka but all improved Medaka can be judged by looking at their fins. So it is sufficient to remember the aforementioned characteristics of the shirivirgin and dorsal fins.
Spawning season is when the water temperature is above 18 ℃and they need 12 to 14 hours sunlight.
Water temperature and daylight hours play a major role in Medaka spawning. They spawn in an environment with the water temperature of 18℃ or over and 12 to 14 hours of sunlight. Even in cold weather, Medaka will spawn if the above environment is created indoors using a heater or similar. In this case, the water temperature should be set at 25 to 28℃ and the light should be kept on for at least 13 hours.
＜TIPS＞
The photo below shows how they are bred indoors. Water temperature is important, but so is lighting. If you are indoors, turning on the lights regardless of the season will help your Medaka grow healthily. Lighting is even more necessary when collecting eggs.
Spawning pars is female > male.
Medaka have compatibility and if it doesn’t match, they will not lay eggs at all. Conversely if the chemistry is good, even a mating of one male and one female could lay eggs every day. For efficient breeding, it is recommended to have a total of 5 to 10 males and females.
Ideally, the male and female ration should be more female than male. If there are two males then three females, if four males then six females to make it work.
Medaka spawn in an environment with a water temperature of at least 18℃ and 12-13 hours of sunlight. Food is also very important for spawning and if Medaka are not well fed, they will not spawn or the number orf eggs laid will decrease. Therefore daily feeding is very important.
If the aquarium contains water plants or egg lying tools then the eggs are deposited on them.
If the eggs are left untouched, they will be eaten or if they hatch, baby fish will be eaten by the parent Medaka so it is advisable to transfer the eggs laid on the water plants or spawning beds to a separate container with some water plants.
Among water plants, the Photinia layer is a common egg laying plant but as it isn’t possible to purchase all year around, we recommend the special Medaka spawning bed from pet shops.
A surprisingly large number of eggs fall to the bottom of the aquarium without attaching. It’s a good idea to pick up the eggs one by one but you can scoop them up when you are changing the water using a net.
You can also transfer the parent Medaka to another aquarium and leave the eggs in the aquarium to hatch. Try a method of collecting eggs which suits you.
The best time to observe spawning is before sunrise
Spawning in Medaka starts before dawn and it is over before sunrise. If you want to observe the spawning, cover the aquarium with a black cloth during the night to make it pitch-dark and create midnight conditions. When the black cloth is removed following morning, courtship behaviour may start and spawning could take place.
The best hatching condition is 250°C/day
Water temperature plays a major role in the number of days it takes eggs to hatch. If the water temperature is higher then the quicker the eggs hatch. The water temperature is law then it takes them longer to hatch.
There is a method called integrated temperature that calculates the approximate number of days that takes for the eggs to hatch.
It tells 250°C days (water temperature (°C) x number of days (days) = 250°C days) for Medaka. So, if the water temperature is 25℃, it takes about 10 days to hatch and if the water temperature is 20℃ then it takes 12-13 days.
Not all eggs laied by Medaka hatch. There are two types of eggs laid which are unfertilised and fertilised. Unfertilised eggs are soft so they crumble when we push a little.
Fertilised eggs are pale yellow in colour and are so hard that they can’t be easily crushed by pinching them hard with fingers. If unfertilised eggs are left as they are, they gradually turn white and become mouldy in the end. If the unfertilised and fertilised eggs are attached to each other, the mould from unfertilised eggs will also invade fertilised eggs. They will become mouldy eventually. If you find unfertilised eggs, it is best to remove it as much as possible so that more fertilised eggs can hatch instead.
＜TIPS＞
The photo below shows newly hatched baby fish. It is recommended to incubate them at 22-26 °C as if they are kept at above 30°C, they will take less days to hatch but they tend to have less colourations.
The photograph below shows baby fish which hatched a few days ago. They are about 4-5mm in body size and can only eat small food. In addition to powered food, feeding them with phylum Pogonophora will speed up their growth and increase their chance to become adults.
Feed baby fish in small amount few times a day.
A very small creature like the tip of a needle swims in the tank are baby Medaka in the aquarium.
Baby fish can survive without food for 3~4 days after birth as they have a yoke sac in their abdomen. Feed them when the yoke sack is gone.
Feed artificial food for baby fish. It is recommended to use as fine grain powdered fine as possible. Feeding is very important as insufficient food can hinder growth so make sure to feed them well.
However you also need to watch out for uneaten food so it is ideal and best to feed small amount preferably few times a day.
Various diseases of Medaka
Diseases which Medaka can get are “white spot disease”,” water mould disease” and “tail fungus disease”. “White spot disease” causes white spots to appear on the body. “water mould disease” causes white lines of mould on the head, mouth parts and fins. Tailstock disease causes withering and melting of the fins. In both cases, treatment is possible in the early stages. Treatment is more difficult in more advanced and severe cases.
Treatment is either with over the counter fish disease medications or just some salt. Salt has to be made to a salinity of 0.3-0.5 % and the sick Medaka is placed in a salt bath. The water temperature should be raised to about 28 °C as disease causing bacteria are less active at high temperatures.
The best way to keep Medaka healthy is to keep them disease free. To keep them healthy by not overcrowding them in the aquarium, changing the water once a week and feed them enough quantity not too much.
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