This is a general section on feeding Daphnia. I have summarised my own
experiences at the end of this section. Daphnia have similar feeding habits to other tiny crustaceans (especially to the likes of Artemia). The best foods for culturing are algae (typically free-living green algae species which tend to turn water to "pea soup"), yeasts (Sacromyces spp, and similar fungi), and bacteria. Combinations of the above seem to have the most success
(i.e. yeast and algae seem to compliment one another). Each food type will be discussed in turn, together with its advantages and disadvantages, and means of attaining/growing it.
Micro algae is consumed in great quantities by Daphnia, and the abundance of daphnia is usually proportional to the density of algal blooms. There are a number of ways to grow algae, all of which are very basic and require little effort.
Placing a container of water outside in good sunlight will usually guarantee a good growth of algae within two weeks, usually a lot less. Algal spores are carried on the wind and will colonise the water, but it usually speeds up the process if you "seed" the water with some algae from a container that has already has a bloom.
Miracle grow, an organic plant fertiliser, can be used to grow algae (after all they're just plants). One method is to use 1 gallon containers, 1 for each day of the week. These sit on a window sill which gets good sunlight for as much of the day as possible. By bubbling air through the containers (an airpump with 7 side lines will do, because there really only needs to be a small movement in the water), algae won't grow on the sides of the containers where it can block the sunlight. Add 1 tea spoon of Miracle grow per gallon. This system is then seeded with green water in tank #1 - two days later tank #2 - two days later tank #3, etc. When this has turned bright green (within 2 weeks), pour it into a Daphnia tank. Refill the container with water mixture and seed with tank #2 which should be about to turn bright green. This is repeated with each container as they turn bright green. As you might be able to tell, this will provide about 1 gallon of fresh green water every two days.
The advantages of algae as a food are that it is very easy to culture and it is excellent for growing daphnia. There are no disadvantages really, other than the fact that it requires bi-daily maintenance / renewal.
There are two general kinds of yeast that we need be concerned about - activated and inactive. Activated yeast is generally a better food to feed because it will not foul the water as quickly/as much as the inactive kind. Bakers, brewers, and almost any kind of yeast are suitable for daphnia cultures, but it is recommended that no more than half an ounce of yeast per five gallons of water be fed every five days. If you're using yeast, especially inactive yeast, consider adding some algae to the water as this will counter any fouling which may result from adding the inactive yeast (this isn't so important with activated yeasts). Do take care not to overfeed inactive yeast as it will foul the culture and therefore kill your daphnia.
Some bakers yeasts come with added ingredients like Calcium Sulphate and Ascorbic acid (vitamin C) to aid fast activation of the yeast. These are harmless to daphnia cultures, but care should be taken when adding this kind of yeast because Ascorbic acid
can give pHs less than 6, which are far from ideal with Daphnia. However, I have never had any pH changes when using such "mixes" in moderation, and the calcium sulphate gives vital calcium for the daphnia's carapaces.
The advantages of yeast as a food are that it's easy to acquire, and there is a minimum of fuss when preparing it for the culture. The only slight disadvantage is that it's not quite as good a food as algae (the daphnia need to consume more weight of yeast than algae to get the same food value). However, yeast is far better than any other food except some bacteria, which have almost as high a food value.
Bacteria have a similar food value to fungi, but they generally reproduce faster than fungi and algae, although the food value doesn't tend to be as high. Bacteria are "cultured" by taking 5-6 ounces of dried horse, cow or sheep dung (dried for two reasons: it's easier to deal with, and most antibiotics or growth promoters which were fed to the animal will break down if the dung is left to dry for a while) and tying it in a nylon bag
(such as tights/pantyhose), and hanging this in the water with the daphnia. Animal dung (including human dung, though don't use human faeces unless you want typhoid or worse...) contains copious quantities of bacteria from
the digestive system, and these will leech out of the dung into the water and reproduce. Typically, the water will go cloudy after a time, indicating that the bacteria are starting to multiply. This should be changed once a week for maximum effect. Another method is to soak the
dung for weeks until it decomposes into a nutrient slurry,
then drip the liquid into the tank at a rate of 16 fluid ounces per
five to eight days.
Another way to culture bacteria in a hurry is to throw a handful of salmon (or
trout pellets), dog biscuits or other meat-based food into a few gallons of
water with some added aquarium water. Within a few days it is usually cloudy
Bacteria are a good food source, and easily acquired/cultivated. The only downside is the smell of the
decaying matter (which can be pretty bad at times). An important thing to remember is that horse dung usually contains tetanus (also a bacterium), so care should be taken when handling it (make sure you have no open cuts/sores on your hands or arms).
These include bran, wheat flour, and dried blood. These should be considered similar to inactive yeast, and the same amounts and care should be taken when administering them. The only real difference is that the food value isn't as high as the corresponding weight of yeast.
Some of My Own Experience
Unless you have a very large container, like an outdoor pond, I don't think
"green water" is worth the effort. I fertilise the water with salmon pellets (the
Axolotl Colony's at the moment - May 2000). The amount depends on your container size and current daphnia population. Too much and you foul the
water and everything dies. As a guide, I would say for a 4 foot long aquarium one
or even two handfuls is enough to fertilise the water if there is an already healthy population of daphnia. If you have less, then
don't use as many pellets or the bacteria population will go out of control.
this is reliant on temperature, ideally in the early 20s celsius / ~70F.
People recommend green water as the best food for daphnia. I would have to say that I mainly agree with this, but I think that bacteria are just as
nutritious. I haven't bothered feeding green water to daphnia since 1998 so draw your own conclusions. I've been maintaining two populations since
June 1998 and they have never completely died out. They do pulse though. If you want a recommendation for a quick fix substitute for green
water, get yourself a bag of frozen peas and one of carrots. Mix about 80% peas and 20% carrots together and then stick them in a food blender. Blend
these until you have a mulch. You're looking for the "juices", so take any liquid and squeeze the mulch to get all of the liquid from it. This
contains particles of a size small enough for daphnia to sieve from the water (less than 50 microns). It's far more concentrated than water
with algae in it, so use it sparingly. It gives just as good a result. I've used this a few times, but I'm just too lazy most of the time
to bother with anything except rotting pellets.
One final note on pellets - don't crush them much first. If you do you'll release all of the nutrients at once instead of over a few days and you
can get the bacteria going out of control. I should mention that I also keep water slaters
(the European fresh water louse) in my daphnia cultures because they break down solid waste and prevent the pellets from being covered in
fungus and floating at the surface. The fresh water louse is a crustacean
that looks like a wood louse and it is not a fish louse (louse is just the
name). I don't recommend snails in the culture either because for one thing,
some species can act as a parasite vector, and also because they use up calcium and
that's reserved for the daphnia!
I've heard of ground-up liver in water being recommended. In that case it's mainly the blood that is the fertiliser. I've tried
animal's blood and found it ok, but the pellets win in my opinion, followed by algae and the mixture I