Culturing Daphnia for Medaka
Culturing daphnia is quite easy. I dabbled with various methods (green water, dry spirulina, dry chlorella, yeast, etc ) but by far the easiest is simply growing them in pure green water. I will also link to another article I call my “Two Bucket system” for creating green water.
Keeping the daphnia is simple, find some water containers to store them in and if possible have as many containers as you can as backups if you have a culture collapse. I bought 4 x 7 litre cookie jars from Big W for about $7 a piece. I keep two inside at room temp and two outside. If you only have 1-2 cultures of daphnia you risk losing them all at once. In all I probably have about 15 cultures I can take from, a couple of outside buckets, the cultures active in my baby medaka tubs, etc.
It should be known that no matter how much green water you put in any container, the daphnia will breed in population to eat it, at any capacity. Its also the reason you have to be careful not to get daphnia in your green water making buckets, since they’ll eat it all and you will have no green water. So you will be forced to either regularly add more green water, or remove daphnia. I recommend both, feed the daphnia to your fish regularly and if possible replace the cultures water weekly or when ever it loses its greenish tinge. I replace my green water every Sunday. Normally I leave enough in each jar for them to eat all the free floating algae in 7 days and reproduce. To empty the jars for new green water, I simply tip the jars out over a bucket, running the water through a cheap 100micron nylon net. You can buy the 80/100/200/800 micron nets off Temu for a few dollars. The aim is a net with small enough to catch the daphnia and empty them back into the jar with the new green water.
You will read a lot about people feeding with bacteria from yeast or other methods and feeding dry algae types. This is very possible, its also fraught with risk from bacterial blooms and simply the very small daphnia being unable to process the dry algae. Manufacturing of dry algae requires flocculation which increases the size and density of the algae which makes in hard for small daphnia to process.
That being said, my daphnia cultures in my baby medaka tubs grow faster then the ones in my culture jars, I have no idea what they are eating or doing but I assume its a haven for bacteria and algae and they capitalize on it.
Its a small ecosystem, I regularly (3-4 times a day) squirt green water in the extremely small baby tubs to feed both the (1-3 week old) medaka fry and the daphnia, I’m sure they both enjoy it, and there maybe some imbalance in which, daphnia might steal green water away from medaka fry, but there is also the number of baby daphnia being consumed by the medaka fry to offset. I try and not have too many full sized adults, just enough to keep producing babies, it generally apparent of fry start losing condition as their stomachs will not look full. Also another reason clear containers for very young fry are warranted, to keep an eye on stomach sizes.
Daphnia are a very high protein food items that medaka fry are literally hardcoded to eat. Some 200-300micron dry powered fry food can be hard for 1-2 week old medaka fry to ingest, so daphnia are a great self replicating and self sustaining food for them, I also suspect the adult daphnia have no problem eating the 200-300 micron baby fish food, which is why they seem much happier in the baby tubs. After 3-5 weeks medaka fry should be weened fully onto the 200-300micron dry powdered fry food and the presence of the daphnia should slowly disappear as the medaka fry slowly get big enough to rip them apart for food.
I highly recommend daphnia, even over baby brine shrimp, newly hatched brine shrimp are too big for day old hatched medakas, newly hatched daphnia are ideal for any stage medaka to eat, plus the developing adult daphnia the medaka fry cant eat, produce MORE food for medaka fry in the way of eggs and newly hatched daphnia as the subsequent batches of medaka eggs hatch.
Have fun hatching both daphnia and medaka eggs.
