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.

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

[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?

[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. I think it is 12 to 14 days from spawn to hatching, so it will be quite a while before I have any fry.

[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.

[djembekah]

awe she's so cute!!!

[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...

[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.

[Tamyu]

Originally Posted by 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.

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. 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.

[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.

[Tamyu]

Originally Posted by LittleBettaFish

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.