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I keep a few going in a set of open trays on a windowsill--in shallow water, figuring that without filtration or aeration, my carrying capacity is limited by surface area.  I used to just toss them a pinch of dried brewers' yeast or a bit of baby food sweet potatoes every few days, and change their water with aged tank water when I do tank water changes.  I did not get many daphnia out of this--just a few dozen here and there as a treat for favorite fish.  But it kept them going until I saw the light:  during Joe Fleckenstein's talk on live foods at the 2005 MASI show, he said he used a little bit of everything he'd heard people used to feed them, including, most intriguingly to me, paprika.  So I went out and got several things he mentioned--soy flour, spirulina powder, and yeast from the health food store, a big jar of paprika from the international grocery, and (my own inspiration, no blame to Joe) some freeze-dried peas, also from the health food store.  I put all that you see here together--thats 180g or about 6 oz of spirulina powder, 1 pound of paprika, a 3.5 ounce container of the peas, about 4 ounces of soy powder and about 4 ounces of brewer's yeast.  Again, the proportions were simply what I bought of each one, and not specifically Joe's recipe.  I bought a big jar of paprika, so there is a lot of pepper in my version.


I whirled these together in the food processor (with a towel wrapped around it to keep from pepper-spraying myself) until the peas were powdered and all well-mixed.  I put it in a spice jar and sprinkle a bit on the daphnia daily.  I have seen an incredible increase in daphnia yield under this new regimen--so many that I suspect one of my trays actually crashed from overpopulation because I wasn't harvesting them fast enough. 

Here are happy daphnia in their trays on the windowsill:

daphnia trays

I keep them on the windowsill because it's a handy surface; they have also done ok in a closed closet for a time.  Light is not necessary.  The culture gets mucky on the bottom, but that's ok as long as it doesn't get stinky.

Daphnia Tray

I use a baster to harvest them.  You can see how they cluster in the corners of the tray above.  I put the baster there to avoid the mulm from the bottom of the tray:

harvesting daphnia

And I replace the liquid I remove with water from the tanks, because they're supposed to prefer to live in aged tank water.  I never give them freshly dechlorinated tap water, only water from my tanks.  They seem to flourish a little more in the water from my "hard water tanks" which is St. Louis tap water supplemented with a bit of SeaChem LiveBearer Salt.  I top them up at least once a week with tank water, and when the culture starts to stink, once every few weeks to a month, I drain the entire culture into a brine shrimp net, along with whatever goop is on the bottom of the box, and rinse it back into the box with tank water--in effect, doing a 100% water change, but with aged tank water.  I think I have daphnia pulex, which are all caught by the net, but Moina macrocopa (often incorrectly called Daphnia moina) are preferred by many fishkeepers because the newly hatched babies are smaller than baby brine shrimp--great for small fry--but require different feeding techniques because they will slip through a standard commercial brine shrimp net. 


The fish are quite pleased by every feeding of daphnia.  Although in theory they could survive in the tanks for days, they never last very long before the fish chase down every last one of them.

One neat idea for making the best use of daphnia comes from Jack Heller, who calls them excellent "babysitters" for young fry.  If you have to be out of town for a few days, putting some daphnia in the fry tanks helps keep the water cleaner, as the daphnia filter feed on some of the tank waste, and they also will produce babies that the fry can eat (assuming the fry are too small to eat the adult daphnia).  Add a couple of ramshorn snails and your babysitting crew is complete--they will help produce infusoria from the fish waste that the daphnia will eat.

Daphnia vs Moina

Adult Moina, a similar animal from a different genus than Daphnia, are the size of juvenile Daphnia, and juvenile Moina are smaller than newly hatched brine shrimp.  I recently got another starter culture of Moina because the very small juveniles should be excellent for fry.  They're so small that they don't have enough density of pigment in their bodies to appear orange to the naked eye, as the Daphnia do, and they're about the same size as the cyclops that sometimes contaminate and can take over neglected Daphnia cultures.  But though the both critters pretty much look just like white dots to my eyes, Moina swim like Daphnia--jerky short almost random-walk movements--and the cyclops are supposed to swim in a smoother steadier motion.  A closer look at the cultures (the best resolution I can get until I find my macro extension ring for the camera) reveals that the Moina do look just like juvenile Daphnia, and up close, they have an orange cast just like the Daphnia.

Here are the cultures shot side by side (identical scale:  the adult Daphnia are about 2mm long).  
The arrowheads point to Moina in the right image--hard to see, of course, but easier to make out if you view the image larger here, and to a similar appearing juvenile Daphnia on the left image.
Daphnia vs Moina culture

Here they are in more detail, at the same scale for both the larger images and the inset closeups:
daphnia vs moina up close

daphnia moina

daphnia vs moina again

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