# Medaka (Japanese killifish)



## Tamyu

I set up a medaka and shrimp tank a few days ago. (Side note - filter media from a stable goldfish tank is amazing. The tank was instantly cycled.)

This morning I wake up to find that one of the girls is carrying eggs around. It is incredibly cute.










A bit of a surprise to find them spawning so quickly, but at least I know they like the tank.:lol: 

I wonder who the father is... I have gold, white, and wild medaka in there.


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## MollyJean

Are the white spots natural coloring? And yes, it is cute! Not many eggs, is it? How long til they harch, and what do you feed them?


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## Tamyu

The white spots are iridescent scales - the gold and wild varieties have them, and the "white" variety is nothing but them. You normally can hardly see them, but they shine silver when they catch the light. 

They usually only lay a few eggs at a time, (10 or so) and carry them around like that for a while. After so many hours (four or five?) she will string them on to plants. 
The eggs take forever to hatch. :-D I think it is 12 to 14 days from spawn to hatching, so it will be quite a while before I have any fry.


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## Romad

What a great picture! It's not every day that we get to see something like that. Thanks for sharing it and keep us posted on the fry.


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## djembekah

awe she's so cute!!!


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## Tamyu

Unfortunately, she was still holding on to the eggs when I left...
When I got home, they were nowhere to be found. I guess she attached them to something where they were promptly eaten by either her companions or the shrimp. I even lightly vacuumed the tank to see if any had fallen into the substrate, but no sign of them. There were only five or six to begin with, so oh well... 

These little guys are like chickens though - as long as they are well fed and happy, they will lay a few eggs almost every day. I will check again tomorrow morning and update if I find some more. Tomorrow I should be home all day, so will probably be able to move the eggs over into the hatchery. I got it all set up and running this morning...


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## LittleBettaFish

Nice photo of your medaka. They are really quite an underrated fish though I wish they would stop selling them as strictly coldwater here. Someone needs to explain what the word 'temperate' means to some stores.

It's weird watching them carrying eggs around. My Oryzias woworae do it and it took me a minute to realise what it was.

Can you artificially hatch their eggs like with killies and other egg-layers, as I haven't really read much about breeding them and they do have access to a breeding mop.


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## Tamyu

LittleBettaFish said:


> Nice photo of your medaka. They are really quite an underrated fish though I wish they would stop selling them as strictly coldwater here. Someone needs to explain what the word 'temperate' means to some stores.


But... Aren't they coldwater? I have always understood temperate to mean "less than tropical, but still needs heating over the winter" - as long as these guys don't actually freeze, they are fine and just hibernate in the winter... And that is only if they can't find food. If you keep feeding them, they will stay awake and active even in very very cold water.

There is a Taiwanese variety that seems to be sold mistakenly as medaka that does need higher temps (subtropical).



> Can you artificially hatch their eggs like with killies and other egg-layers, as I haven't really read much about breeding them and they do have access to a breeding mop.


I don't know what you mean by artificially. :lol: After they stick the eggs on to something, they are pretty much oblivious to them (and everyone but the mother will eat them). So it is best to just take the bit with the eggs adhered out and stick it in another container. They usually lay the eggs in shallow pools, so the eggs are quite strong. You can put them in a cup and just leave them until they hatch.


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## LittleBettaFish

This is the info Seriously Fish gave and they are generally a pretty good site:



> This temperate to subtropical (NOT coldwater) species is subject to seasonal temperature fluctuations in nature and is most comfortable between 60 - 72°F/16 - 22°C.


So I think while they can live at colder temperatures (we get down to around 0-10 degrees Celsius in winter here) they prefer a temperature somewhere in the middle, which is what I always took temperate as meaning. Mine are being kept at 24 degrees Celsius as they are in with my honey blue-eyes who prefer a higher temperature.

As for artificially hatching, with killifish and my pseudomugil I pick the eggs out of the spawning mop daily as the adults will generally go through and eat them. Then I put them into a separate container (mine floats in my fry grow-out) add a couple drops of methylene blue to deter fungus and gently aerate with an airstone. 

Once the fry hatch in the container they are acclimatised over into the grow-out and raised as normal.

I love the Oryzias species. Just wish they were more readily available here.


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## Tamyu

LittleBettaFish said:


> So I think while they can live at colder temperatures (we get down to around 0-10 degrees Celsius in winter here) they prefer a temperature somewhere in the middle, which is what I always took temperate as meaning. Mine are being kept at 24 degrees Celsius as they are in with my honey blue-eyes who prefer a higher temperature.


I prefer to keep mine at as close as possible to their natural environment... With medaka, they are basically seasonal breeders. They breed based on the temperature and the daylight hours. As they don't stay in breeding shape all year in nature, their bodies cannot handle it. Keeping them in a heated tank may seem "happier" because they are always in breeding mode... But it seriously reduces the quality of the eggs and fry, and cuts their lifespan down to less than half. Medaka bred year round (kept at "optimal" temps) have short lifespans and tend to reach maturity at a smaller size and stay sort of stunted as they never have a good growing period without their bodies pushing toward reproduction.

Wild medaka live in streams, ponds, and pools that freeze over completely in the winter. As the pet versions are pretty much the same as the wild versions in everything but color, they do best in the same sort of environment.



> As for artificially hatching, with killifish and my pseudomugil I pick the eggs out of the spawning mop daily as the adults will generally go through and eat them. Then I put them into a separate container (mine floats in my fry grow-out) add a couple drops of methylene blue to deter fungus and gently aerate with an airstone.


I would say yes then - you can artificially hatch the medaka eggs with no trouble. If you leave them attached to a plant, or remove the little strings that stick to plants and such, they hardly ever develop mold unless they are dead eggs to begin with. 



> Once the fry hatch in the container they are acclimatised over into the grow-out and raised as normal.


I have a nice little unit tank that attaches to the normal tank, doing a constant drip exchange of water. They can be moved pretty much immediately into the tank after hatching as it is the same water. 



> I love the Oryzias species. Just wish they were more readily available here.


I caught my wild ones myself. :-D


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## Fabian

The anal of those killifish will form cups and the eggs will be stored in it.


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## Tamyu

Fabian said:


> The anal of those killifish will form cups and the eggs will be stored in it.


Maybe other types of killifish... But not medaka. They carry the eggs for a few hours and then stick them onto something. They aren't even really killifish - supposedly they were misclassified because they look like killifish and carry eggs. They have been grandfathered in as honorary killi.

If her eggs are gone, they were stuck on something and eaten.


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## LittleBettaFish

I was so excited to see one of my daisy's rice fish carrying eggs and I had hoped if I put a spawning mop in I could save some. Turns out from the looks of things all of mine may be female. One of them was also a pygmy perch, don't know how he snuck in!

My medaka have shown no signs of carrying eggs at all, but then again if they did they would be eaten pretty quick by my blue-eyes. They are only living in that tank for a few months and then they can have a tank to themselves in my fish room. 

Have you got any photos of what kind of habitat your medaka come from Tamyu? I love setting up biotope style tanks but sometimes it can be difficult to find good resources online.


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## Tamyu

LittleBettaFish said:


> My medaka have shown no signs of carrying eggs at all, but then again if they did they would be eaten pretty quick by my blue-eyes. They are only living in that tank for a few months and then they can have a tank to themselves in my fish room.


If they are stressed at all they won't lay eggs... But if they did, I think you would notice. They lay them in the morning and carry them around for at least five or hours. Those carrying eggs are pretty protective of them and will keep their distance from other fish. 

Mine laid eggs again, but she seems to not know how to stick them to things properly and keeps letting them fall off to the substrate where I can't find and retrieve them. :-( She is the largest of the females but still pretty small, so I am guessing she is still a juvenile getting used to spawning. 

Another thing - they can be picky about water and food for spawning. It is really easy for me to keep them as my water is in their normal range. I also use special medaka water conditioner, medaka vitamin and mineral supplement, keep them in a tank designed for medaka, and have special medaka soil and gravel in the bottom... Oh, and also feed them special medaka formula. So they are are very spoilt. :lol:



> Have you got any photos of what kind of habitat your medaka come from Tamyu? I love setting up biotope style tanks but sometimes it can be difficult to find good resources online.


Hmm, I don't have any in water pictures... I plan to head back this weekend to see if I can catch a pair of tiny goby. Last time I only found one, but they are social so I put it back. Once I put one in my aquarium, I would be stuck with it... And if I never found another it would live a very lonely life. So this time I will cross my fingers that I can catch two or three.
I will try to take some photos of the location and see if I can get some that show into the water well.


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## Tamyu

So far I have been able to collect about eight of her eggs off of the substrate and branches in the tank. :lol: I don't know how many of them are fertilized, but at least a few are (I spotted eyes!)

I haven't had a chance yet to go out and take pics yet, so here is a photo I found of a similar location. Medaka live in places like this:









They live in the rice paddies when they are filled with water, and hang out in the small agricultural streams when they drain the rice paddies. I caught mine in a stream between rice paddies.

There is a medaka museum fairly close to me - this is their biotope setup (looks almost exactly like my tank... Except I have white substrate that supposedly helps keep the water perfect for medaka.):









And... Medaka in their native environment - the rice paddy. :lol:


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## LittleBettaFish

Here's my current medaka/blue-eye set-up










I'm going to be doing some biotope style tanks for my Aussie natives (you can see my rainbowfish tank to the left) so their habitat looks fairly similar to what I had in mind.

I hate all these places you can pull decent fish out of ditches and rivers. Here all we seem to get is useless carp and pest mosquito fish. Too far south to get the tropicals they get up in the north.


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## Tamyu

LittleBettaFish said:


> Here's my current medaka/blue-eye set-up


Taking a look, it might actually be too much vegetation for them. They like to hang out in open areas, and will only really retreat to plants when scraping their eggs off. I have about a quarter of my tank planted, and they almost never go into them unless they are chasing after sinking food. They are also always out in the open when you see them in the wild. They will hide under floating plants, but they don't go into anything dense. Reedlike stems are more their type of vegetation. They actually seem to go out of their way to avoid anything with large leaves.



> I hate all these places you can pull decent fish out of ditches and rivers. Here all we seem to get is useless carp and pest mosquito fish. Too far south to get the tropicals they get up in the north.


Hahaha... To me, medaka are pretty darned boring when it comes to fish as, well, I can pull them out of ditches. :lol: They are really similar to betta when you think about it, as they live in similar conditions (the still or barely moving water of rice paddies and the related ditches and waterways) just in a much much cooler climate. 
If betta are the national fish of Thailand, then medaka are the national fish of Japan.  They are seriously everywhere here.


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