12/09/2021
***How to Culture Daphnia***
Daphnia are an excellent food for your fish providing protein of 45-70% and lipids of 11-27%, as well as the thrill of the chase! The tiniest of daphnia are excellent food for young fry or nano fish, and the largest are enjoyed by all omnivorous or carnivorous species. They are also excellent food for many amphibians.
HOUSING
Daphnia can be raised in anything from a mason jar or vase in a sunny windowsill to large tubs or pools of water outdoors. They do not require aeration or filtration.
I keep floating plants in all of my outdoor cultures to provide passive filtration. Snails are also an important denizen, as they will act as your janitorial crew by feeding upon the shed exoskeletons of the daphnia.
When kept outdoors, you will want to keep the cultures covered by fine mesh or screen to keep insects with predatory larvae from laying eggs in the cultures. Dragonfly and damselfly larvae love daphnia as much as our fish, and can quickly wipe out your entire population of daphnia.
My cultures are on the east side of the house in a shaded location. In the winter months it would be best to maximize sun exposure, so a southern location would likely be optimal.
LIFECYCLE
In a healthy colony, daphnia reproduce asexually, producing all female young. The female produces eggs which are released into and hatch in her brood chamber which is under her carapace. At her next molt, the free swimming young are released. Those female clones start reproducing after four to six instars (molts) which takes about six to ten days depending on water temperature.
When conditions become adverse such as a lack of food, insufficient oxygen, temperature extremes, or ammonia spikes due to overcrowding, (such as when a vernal pool starts drying up), they produce male young which will then fertilize the eggs of the female.
Often called "resting eggs" these are encased in a hard case (ephippia) on top of the carapace, and are released when the female molts and then sink to the substrate. When conditions become favorable again (spring rains, presence of food in the water column) they will hatch and begin the life cycle again.
For this reason, should you inadvertently "crash" your culture, do not siphon the bottom of your culture container. This is where the eggs are. Instead, do a water change and fill with fresh greenwater and the culture should rebound in a matter of days.
The same applies if you have harsh winters and the culture freezes. Even if allowed to dry out completely, in the spring when conditions are favorable, your colony will miraculously come to life once again.
TEMPERATURE TOLERANCE
My cultures have done well outdoors in a shaded location even when temperatures reached 110F, and the morning water temperature currently is reading 50F. One culture has been iced over twice this year with no ill effect.
Production has slowed down with colder weather, but the colonies are still producing adequately.
FEEDING
Daphnia are very easy to raise when fed greenwater, but it takes some trial and error if you have to feed spirulina algae powder and/or activated yeast. My first two attempts resulted in culture crash due to being too generous with the feed. Less is definitely more when it comes to giving them "prepared" foods.
GREENWATER CULTURING
To culture greenwater you simply need to set a container of water in full sun. Daphnia are very sensitive to chemicals, so if you are on municipal water it is best to use aged tank water. Adding some filter mulm or the detritus from gravel vacuuming helps by adding bacteria and infusoria, which the daphnia also feed upon, and snails will produce waste to fertilize the algae. A bit of blanched cabbage, banana peel, or straw will provide even more food for the microscopic life in the culture.
If your greenwater culture is outdoors and you add some dead dry leaves to form a layer of detritus on the bottom, you will likely be able to harvest bloodworms (midgefly larvae) from the container as well. When harvesting greenwater from an outdoor container that lacks a cover, make sure to strain it through a fine mesh media bag (or go to Dollar Tree and buy a pack of mesh party favor bags!) in order to ensure you are not introducing predatory larvae to your cultures.
Some people add urea fertilizer to the water, but my attempts resulted in high ammonia. Occasionally I will add some rabbit manure which is an excellent natural fertilizer.
You will need to keep your daphnia in a separate container than your greenwater culture or they will eat it all in a matter of days. This happened to my primary greenwater tank when I was out of town for a month and my husband was caring for all the critters- somehow he "contaminated" the greenwater vessel with daphnia.
Upon my return, I was flabbergasted because the tank was clear. "How in the world did you manage to kill off my ALGAE, of all things?!?" Upon closer inspection, I saw that there were thousands of daphnia in the tank. To prevent that from happening again, I added a couple of mosquito fish to eat any interlopers.
SPIRULINA ALGAE/ACTIVATED YEAST
When I fed spirulina and yeast due to the contamination of my greenwater tank, I mixed a teaspoon of algae, 1/4 teaspoon of baker's yeast, and 1/2 teaspoon of sugar to a gallon of water. This fed cultures comprised of about 180 gallons of water. I only mixed up enough food for one feeding- for some reason the spirulina will turn blue if left sitting, and I am unsure if that renders it unsafe.
To prepare the mixture, partially fill a jug or bottle with water between 100-110F. This temperature will activate the yeast or make it "come to life." Add the sugar and allow it to dissolve prior to adding the yeast. Allow the yeast ten minutes or so to consume the sugar and then add the spirulina powder, shaking the bottle vigorously since the algae tends to clump up. Fill the balance with tepid water.
Feed only enough to cloud the water in your culture slightly, and add more once the water clears. Remember to be very sparing and do not give in to temptation to overfeed or your culture will likely crash.
INSURANCE
Always have several back up cultures in case one colony crashes. I have a vase with houseplant cuttings and a few ramshorn snails in a sunny windowsill which is fed only by topping off periodically with greenwater.
CONCLUSION
You should now be ready to start your very own daphnia cultures! They are fascinating little crustacean that are fun to keep in their own right, and an excellent and prolific choice of food for your aquatic pets.
