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Daphnia, also known as water fleas due to their jerky swimming movements, are simplicity itself to culture, as most daphnia are females and produce live young regularly if adequate food is present. Daphnia can be easily cultured if suitable water conditions and food are provided. Daphnia are commonly used to detect various water pollutants. They are sensitive to chlorine and various heavy metals.
There are perhaps 100s of species of daphnia. We grow two species of daphnia (magna and pulex) and a related species, moina (sometimes referred to as "Russian Daphnia). We culture all the same. Magna hold some sort of facination because of their size. While we find that they are larger (impressive perhaps) they do take longer to get to their adult size and more resource (tankage and food) to be maintained in sufficient quantities for most applications. We like moina because the adult moina are small...and the new born are smaller than newly hatch brine shrimp...however, try to harvest the newly hatched moina is beyond the scope of brine shrimp nets (too large of openings), making their use impractical for most folks. Moina has an additional advantage that may make harvesting pain worth the gain. Moina has an extraordinary ability to withstand "normal" heat of summer and stay in production. Most daphnia fades with heat, moina however has done well for us into the upper 90F ranges for weeks at a time.
However, all advantages of either size of heat resistance aside, pulex is prolific, sized appropriately for the majority of fish we work with and hardly in our environment (we harvest year round with some ebb in the mid-winter and the very hottest of the summer).
We have been experimenting with techniques to grow pulex indoors. For the past year we have been using quarts, gallon and 5 gallon sized containers with great success. While we have grown all three daphnia in our experiments, it seems that pulex produced the most mass for the container sizes.
If you do not have the facilities to grow daphnia either indoors or outdoors, you may want to consider Grindal worms. Grindal worms can be a suitable alternative to daphnia in many situations...and you can grow them in a shoe sized or sweater sized plastic box (under the bed for some of our clients).
For our out-or-door cultures, we use water from the tap to feed our Green water cultures and let the extremely dense bio-mass of our greenwater cultures render the water safe for the daphnia. If using either the Green water or chemically pure water is not possible, unpolluted water from a nearby pond or stream may prove satisfactory. However, water from "natural" sources can be a source of contaminant creatures...some good for fish, some not good for fish, but nearly all either compete with daphnia for food or eat daphnia as food. Water from long established, freshwater aquariums can also be used, however DO NOT use water that has been treated chemically for disease control.
Fill the container about half full of appropriate water and add your daphnia culture. You will fill the container over the next several days as the colony grows. You should prepare your culture tank within a day or so after you order the daphnia. Floating the daphnia culture in the new culturing container is a good idea. These are living organisms and will be shocked, perhaps in a lethal manner by extreme differences in the temperature. Immerse the daphnia culture into your tank gently do not pour through the air. Air can easily be trapped beneath the daphnia's carapace and they will rise to the surface and die. They do not have a way to rid themselves of the air.
Feed the daphnia Green water. We harvest
the daphnia by removing ½ have of the water through a net. We do this every day and fill
the container with Green water. On a hot day this could result in the water becoming
depleted of oxygen and cause your daphnia to perish, so care must be taken not to feed the
daphnia too much.
It is important make frequent observations regarding the health of the culture because once the daphnia consider the environment unfit (for whatever reason), the females start producing male offspring and then only ephippial ('winter eggs') are produced. These eggs will not hatch until they have been subjected to several cold cycles, so your culture slowly fades away. When this happens frequently it is not possible to build the culture back to harvesting levels and you have to wait until the next spring to begin harvesting again.
Daphnia are filter feeders. They filter single celled algae and other foods from the water. Large blooms of algae cause the water to appear green and hence the term "green water." For some, growing green water is a real challenge. We us a large aquarium in the backyard with a number of overfed feeder goldfish to produce Green water for the daphnia cultures. It is nearly foolproof and produces about 25 gallons of Green water each day. We also use plastic garbage cans for producing greenwater...also with goldfish as fertilizer suppliers.
Glass aquaria, plastic buckets or a child's wading pool can be used to culture daphnia. The larger the container the "safer" that the culture will be from changes in the environment and the water qualities. We have grown daphnia successully in quart, gallon and five gallon containers. The smaller the container the more attention you will need to pay to the environment...food, water quality and temperature. It is fairly easy to monitor a one gallon container...we have done so many times and for extended period...on the kitchen counter. The kitchen counter cultureing also has several advantages...relatives don't come to visit too frequently an the kids don't ask, "what's for dinner."
We use 25-gallon tubs to culture the daphnia in. As previously mentioned, daphnia are very sensitive to metals, so don't use water fresh from the tap, either pond water or aged water from tanks, or as in our system, Green water from a large and stable source. The amount of Green water required for a 25 gallon container such as we use should be dense enought to make it more-or-less impossible to see 12 inches in to the water column (in the photo, the white device is a piece of PVC plastic with a fitting on the end. You can not distinguish the fitting because of the density of the algae). Any less dense and the colony of daphnia will have to be feed more frequently (in our situation), too much more and the oxygen content will be lowered in the culture, also endangering the daphnia. When the water clears, most of the algae is gone and the daphnia should be fed again. However, we have found that instead of waiting until the Green water is cleared we enjoy the routine of harvesting every day. By harvesting every day, the daphnia get their water changed regularly and we are assured of their getting enough food.
Harvesting and feeding every day assured that the daphnia are also getting a regular well baby check at the same time. It is a good opportunity to look for potential challenges before they become problems. In those situations where cultivating a good batch of Green water is not possible, daphnia can be maintained on other foods.
We have been "experimenting" with several alternatives to greenwater. While we still feed the majority of our daphnias greenwater and consider the greewater to be the best food (and easy for us) we have a numbe rof clients who live in situaitons where outdoor cultivation is not possible. We have been surpirsed and plesed to find that cultures can easily be maintained indoors in gallon and five gallon containers. A one gallon glass jar can develop a colony of daphnia large enough to supply a few adult Bettas with a live menu item every other day.
By accident (they do happen), be found that daphnia do very well on a product called "Liquifry." We grabbed for a bottle of another product we were testing and picked up a bottle of Liquifry instead...a drop per day in a one gallon colony seems to be the right amount...it varies with the density of the colony.
Using a gallon jar and Liquifry allows a person living in a small apartment to grow daphnia.
There have been foods like Sweet Potatoe discussed on the internet.
Some folks use a yeast and water solution for feeding daphnia. If you choose to use the yeast-water method, the mixture is simply yeast added to water and dissolved and that mixture is added to the culture container with the daphnia. It would be unwise to add the yeast directly to the culture, as the change for adding too much is very real. The mixture should give the culture container a faint "haze" but not be "milky.: When you add the yeast mix to the culture you will see what we're talking about. Its hard to describe but easy to observe and understand.
We found a question and answer on the WWW that you might find of interest:
"What do water fleas feed on?
Water fleas are filter-feeding crustaceans. (They are called water fleas because of their small size, but they are not fleas at all.) Their shell-like body protects their swimming and feeding appendages. They feed by sieving the water to extract phytoplankton or detritus. A few species of water fleas are predacious but most are herbivores or detritivores, feeding on phytoplankton, attached vegetation or decaying organic material. Small particles in the water are filtered out by fine setae on the thoracic legs and moved along a groove at the base of legs to the mouth. Although there is some evidence that certain types of food, such as particular types of algae, Protozoa, or bacteria may be selected by some species, it is generally believed that all organic particles of suitable size are ingested without any selective mechanism. When undesirable material or large tangled masses are introduced between the mandibles, they are removed by spines on the first legs and then kicked out of the carapace by the postabdomen."
"We grow food not bait"