きれいに撮れた奇跡の一枚

How to raise killifish (Oryzias latipes) eggs and the difference between males and females.

  • 2022年11月18日
  • 2022年11月21日
  • killifish

Egg-laying season for killifish in a natural environment is from May to October

When kept outdoors or without a heater, medaka killifish lay eggs generally from May to October each year.

After October, even if they lay eggs, the eggs may not hatch due to low water temperatures or the fry may not grow well.

A heater may be necessary for breeding after October.

Year-round breeding is possible with a heater

Year-round breeding is possible if a heater is installed.

There is a risk of shortening the lifespan of killifish because they are artificially made active at a time when they are hibernating in their normal natural environment. It would be a good idea to introduce heaters if your goal is to breed or improve the breed.

If you have a male and a female, they will usually spawn before you know it

Breeding killifish is one of the easiest of all ornamental fish.

They will spawn easily if you have a healthy adult male and female.

A killifish capable of spawning is about 1.5 cm or larger

Under good rearing conditions, killifish begin mating and spawning 5~6 weeks after hatching, at a size of 1.5 cm or more in length, when their fins and other organs are formed.

Because they have a short life span and many external enemies, they seem to mature quickly.

Not a single female lays eggs! Why?

If you are keeping multiple killifish and they are not laying eggs at all! What is the cause?

First, let’s check if there are males and females

Distinguishing between male and female Killifish is easy once you get used to it.

You can distinguish between males and females not only by their appearance, but also by their reproductive behavior.

A beautifully taken miracle

Male medaka characteristics

  • Large dorsal fin
  • Cut or cleft at the base of the dorsal fin</li
  • Rump fins nearly parallelogram-shaped</li
  • Bigger butt fins
  • Smaller ventral fins than females

Female Orochi killifish

Female killifish characteristics

  • No cut or tear at the base of the dorsal fin
  • Ventral fin larger than in males
  • Rump fins nearly triangular

Only healthy males and females will spawn

Only killifish in good health will mate and spawn together.

Male killifish do not seem to court weak females, and if the male is weak, they will not mate.

Note that many recently bred killifish are weak!

With the recent killifish boom, we see a lot of breed-improved killifish being sold at home centers and pet stores, but we feel that many of them are weak.

It is healthy females that lay many eggs. Be sure to buy from a reputable store that sells healthy killifish. Purchase from a reliable shop that sells healthy killifish.

My hybrid. Unique and beautiful

Compatibility between killifish is also important

No matter how many males and females you have, just like humans, if they are incompatible, they will not spawn easily.

Studies have shown that killifish with different body colors are not interested in each other.

Although this is not much of a concern, if a healthy male and female killifish do not lay eggs easily, it may be a good idea to try adding another individual.

What to do if they lay eggs? Let’s quarantine the eggs

So, what should we do once the female has successfully started hanging eggs? First, collect the eggs.

If they are left with the parent killifish as they are, the fry will be preyed upon by the parent killifish immediately after birth.

Note that killifish will eat most of the zooplankton that can fit in their mouths. So here is an introduction to the egg collection method.

How to collect killifish eggs: Collecting eggs directly from the female

Collect the female killifish with a net and collect the eggs directly from the killifish using your fingers or a brush.

This method has the advantage of ensuring that all eggs are secured, but has the disadvantage of being physically taxing on killifish and labor intensive for humans.

It's quite labor intensive and also puts a lot of strain on the killifish.
Quite labor intensive and taxing on the killifish

How to collect killifish eggs: collecting them from spawning beds

This is probably the most common method. Eggs laid in water plants or on artificial spawning beds are collected one by one.

It is less stressful for the killifish and easy to collect. In our house, we float balls made of moss and let them lay their eggs in them.

Medaka spawns just by floating moss balls
Moss. Medaka spawns just by floating

How to collect killifish eggs: Collecting fallen eggs

If the situation is not covered with gravel or other materials, it is possible to collect fallen eggs.

You can also collect the eggs by simply filtering them through a net when you change the water with a water change hose. A dropper for tropical fish or killifish is also recommended for ease of use.

How to raise killifish eggs

Hatching even if you just put them in tap water

Actually, hatching killifish eggs is not that difficult.

If the eggs are properly fertilized, they will hatch simply by placing them in tap water.

Total temperature for killifish eggs to hatch is 250°C

The total temperature for hatching is said to be 250℃. This means that they will hatch if kept at a water temperature of 25°C for 10 days. A lower water temperature will result in an additional few days, and a higher water temperature will result in a shorter time to hatching.

You can use methylene blue with or without

Many people use a chemical called methylene blue solution, which is effective against fish diseases, but it is very effective but requires caution.

Because the staining power is too strong, it is troublesome if it gets on clothes or hands.

Breeding both eggs and fry is easy as long as you keep them in a large container with plenty of room to spare.

Methylene blue solution commonly used to treat fish diseases
Fish Methylene blue solution commonly used to treat fish diseases

Common mistakes

Eggs turn white and moldy

Unfertilized eggs quickly become cloudy white due to water mold. If not removed early, even the fertilized eggs will be contaminated by water mold. To prevent water mold contamination, break apart each egg you collect. Medaka eggs are surprisingly tough and will not be broken by a slight touch with your finger.

Fry do not grow due to poor water quality

From spawning to hatching often goes well, but raising fry is the most difficult part of killifish keeping. I will not go into detail about raising fry here, but I think that in many cases, fry do not grow well due to poor water quality or lack of food.

The main points are to keep them in a large enough container and to feed them as much food as they can eat.

Related Articles

This website provides information on how to keep killifish.
Please take a look at our other articles.

Related

Ecology and biological and morphological characteristics of medaka Standard Japanese Names: northern medaka, southern m[…]

水槽の底に茶色いもやもやした汚れがあったら水換えのサイン!
Related

Having trouble keeping killifish fry? [caption id="attachment_2628" align="aligncenter" width="1024"] Aim to be full of[…]

稚魚がいっぱいを目指そう
Related

Conditions for killifish to spawn First, let's keep in mind the conditions for killifish to spawn. When the killifis[…]

初心者や子供でも知識があればメダカ飼育は簡単
Related

Medaka keeping is easy even for kids once you get the hang of it! Medaka are probably the easiest type of fish to keep […]

導入初日から澄んだ水になる
きれいに撮れた奇跡の一枚
『次世代のおさかな好きを創る』をテーマに毎日更新中!