Culturing Daphnia

[jest1081]

Main Site : http://www.caudata.org/daphnia/

Physical Requirements

Salinity - Daphnia are typically freshwater organisms and there are no marine species of the Daphnia genus. 99% of Cladocerans are found in freshwater, and the remaining few species are mostly found in brackish, not sea water. Some species have been observed in salinities up to 4 ppt, and salinities of 1.5 to 3.0 ppt are common in pond cultures in the Orient.

Oxygen - Daphnia are generally tolerant of poor water quality, and dissolved oxygen varies from almost zero to supersaturation. Like the Brine Shrimp, their ability to survive in an oxygen poor environment is in their ability to synthesize hemoglobin. The production of hemoglobin may be promoted by high temperatures, and a high population. Also, like brine shrimp, Daphnia are not tolerant of fine air bubbles. A slow aeration is needed with Daphnia as a large bubble column will strip the Daphnia out and kill them. I (and a number of others), have found that Bio-foam filters (designed for fry-tanks) are ideal for aerating Daphnia culture, and the removal of larger particles from the water is an added bonus. However care should be taken to use them at minimal air flow to avoid over-agitating the water.

pH and ammonia - A pH between 6.5 and 9.5 is acceptable, with the optimum being between 7.2 and 8.5. Ammonia is generally highly toxic to all organisms, even in small amounts, but in alkaline conditions, the toxicity is radically increased, and this will drastically impare Daphnia reproduction, but will not affect the actual health of the animals themselves. So it seems that on the small scale that we require, monitoring of pH and ammonia is not critical to success. NOTE: in general, the more extreme the pH, the higher the toxicity of dissolved minerals and gases. Also, remember that pH is a logarithmic scale - a pH of 5 is ten times more acidic than a pH of 6, and likewise, a pH of 9 is ten times more alkaline than a pH of 8.

Dissolved minerals - In contrast to their tolerance of low oxygen, Daphnia are very sensitive to disturbances of the ionic composition of their environment. They become immobile and eventually die with the addition of salts like sodium, potassium, magnesium, and calcium. Low concentrations of phosphorus (less than 0.5 ppm) will stimulate reproduction, but concentrations higher than 1.0 are lethal to the young. Daphnia magna are quite resistant to phosphorus and can withstand concentrations as high as 5-7 ppm. Daphnia are not affected by the addition of nitrogen in fertilizers for the promotion of algae growth. As with any aquarium venture, the water used should be treated with aeration or de-chlorinator to remove chlorine before the culture is started. Concentrations of only 0.01 ppm copper will result in reduced movement in Daphnia. They are extremely sensitive to metal ions like copper and zinc, pesticides, detergents, bleaches and other dissolved toxins. For this reason, they are often used to test waste-water from industry. Municipal and well water may be contaminated enough to kill the culture. The best source of water is from your aquarium water changes, but you could also use filtered stream or lake water (fish-free water bodies are recommended due to possible disease introduction to your fish aquarium by way of the daphnia), or rain water collected from areas of low/no air pollution (and rain water collected in cities or industrial areas is usually safe if left to stand for a week and only the top-most 3/4 used). Never use distilled or deionised water, as it does not have the minerals needed for growth.

A small degree of temporary and permanent hardness in the water usually encourages growth and reproduction because Daphnia make use of calcium and other minerals in their chitinous carapaces. D. magna tends to prefer harder water (170 mg carbonate hardness) and D. pulex a little less hard (90 mg carbonate hardness). I usually add a very tiny pinch of powdered Tufa rock (often used in Marine aquaria) to my water because there is very little temporary hardness in the water I use and no permanent hardness whatsoever.

Temperature - Daphnia have a wide tolerance to temperature. The optimum temperature for Daphnia magna is 18-22 oC (64-72F). D. pulex seems to do well at well at almost any temperature above 10oC. Moina withstand extremes even more, resisting daily variations of 5-31oC (41-88 F); their optimum being 24-31oC (75-88 F). The higher temperature tolerance of Moina make this species a better choice where temperatures may rise above the comfort levels for D. magna at certain times of the year.

What do I feed them?

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.

Algae
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.

Yeasts
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
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 with bacteria.

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).

Other Foods
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 Indiana University 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 mentioned above.

How do I maximise the yield?

Daphnia production is relatively simple, if not an exact science. However, there are proven measures that increase the productivity of a culture.

Good aeration (good in so far as the manner in which the water is aerated, not good as in quantity) is probably the largest contributing factor for good production. Some species prefer no aeration, but Daphnia magna seems to do well with it. It allows you to keep more daphnia in the same container. It also circulates the water, (which counters stagnancy and fouling). It minimises the possibility of algae growing on the walls of the container, and it also keeps inert food in suspension which is more conducive to most daphnia feeding habits. The only problem with aeration is that fine bubbles can lodge underneath the daphnia's carapace and float it to the surface and preventing it from feeding. Therefore airstones should be avoided (unless used in a bio-foam filter in which case the air bubbles combine together), or coarse airstones (or better yet, no airstones) should be used instead.
A good method (tried and trusted) of aerating the water which I have mentioned previously is the bio-foam filter (there are a number of models available, any will do). These are commonly used in fry tanks, but are ideal for daphnia. They trap larger particles in the water (they don't trap algae), and help break them down, releasing nutrient for the algae to feed on. The outlets are usually very good at aerating the water, but care should be taken to use them at low to minimum flow to avoid over-agitating the water (we want some aeration, not a torrent). I haven't had a fouled culture yet while using a bio-foam.

Carry out regular maintenance as described in the Maintenance section, especially water changes.

Cull/Harvest the culture regularly (again, see the Harvesting section). This encourages constant growth and also keeps the daphnia from exhausting both the oxygen and the food in the water too fast for it to be replaced.

Some people like to keep a light on 24 hours a day for their daphnia tank as this can encourage faster growth and reproduction. I haven't tried this myself. However, you probably won't need to do this once your culture gets going. One important note though - continuous 24 hour periods in which the daylight is less than 12 hours and with a temperature significantly below 18

Water changes: some people recommend you change up to 75% of the water in a culture every day. This is really dependent on what rate you're "running" the culture at. The more food you feed, the faster the water will be fouled, and therefore the more frequent the water changes. This is really up to the individual, but be aware that output levels will drop if there is a build up of metabolites/toxins/etc in the water. This could lead to crashing.

Maintenance

A daphnia culture requires very little maintenance other than partial water changes (the amount really depends on the volume of water and the number of daphnia in the culture - more water usually needs less changing, more daphnia usually means more water needs to be changed, to a maximum of 50% per week). Do feed your daphnia on a regular basis.

The key to avoiding population fall-off/crashing is to have constantly good conditions, and to avoid sudden changes, such as large temperature drops, culture fouling, or the addition of dangerous chemicals to the water. Remember that if you're keeping your colonies outside, the population will naturally decrease in winter, but should increase again in the following season.

Should your culture die off, don't despair. Either change most of the water or take the mulm and put it in a new container - if conditions are good, the ephippia should hatch within 4 to 8 days (if you accidentally poisoned the culture with chemicals, you may need to obtain a new starter culture because the daphnia may not have had time to produce ephippia, and even if they did, even ephippia will not survive for very long in strong chemicals like bleach or even mild acid).

If you go on holiday for a few weeks, don't be surprised if your daphnia have produced ephippia and the population has decreased while you were away!

[jest1081]

Dos and Don'ts

This section is intended as a reminder of things to remember and a precaution against simple mistakes people often make without realising it.

DOs

Do make sure you age your tap water and have a good idea of what's in it:

If it contains chlorine (chloramine will also put chloride into the water), it must be left to stand or aerate the water for 24 hours to drive off the chlorine gas (fluoride is usually very low in concentration and isn't really something to worry about).

If your water contains lots of ammonia, this will inhibit the population growth of your culture - again, aerating the water vigourously helps drive off ammonia (although it takes a lot longer than with chlorine).

Any metals in the water can often be toxic to daphnia. Some can inhibit population growth (see the section on Physical Requirements).

Do carry out regular partial water changes.

Do feed regular modest amounts of food (this will depend on the culture size).

Do make sure you have adequate water hardness for your daphnia, otherwise they will not reproduce at a high rate, and will probably just produce ephippia.

Do try to maintain a constant temperature (about 20oC is ideal for most species).

Do cull/harvest your cultures at least once a week to avoid overcrowding.

DON'Ts

Don't wash your hands with soap/detergent just before you put your hands in a daphnia culture unless you've _thoroughly_ rinsed your hands because soap and detergents are toxic to daphnia.

Don't overfeed - if anything, underfeed your daphnia to avoid fouling and toxic build-up of ammonia.

Don't put your daphnia in a container of dense algae (and don't change too much water from the tank for algae water at one time) because algal blooms tend to raise pH to very high levels (over pH 9), and coupled with even a low ammonia concentration, this could be disastrous for the daphnia, killing them in short order. Ammonia toxicity increases with higher pH.

Don't keep all your eggs in one basket (or daphnia in one container). Even the best of us will have accidents on occasion or have an emergency, etc, and our cultures may be poisoned or die off for no apparent reason. To counter this, it is best to seed as many water vessels, aquariums, and even flower window boxes with daphnia when the culture is first obtained. This will ensure you will be able to "restart" without too much fuss.

Don't use insecticides near your daphnia containers, and don't leave your daphnia container in a room that was just painted/varnished/etc, because the fumes/gas can be toxic, and even if it doesn't kill the daphnia, the fish you feed them to may be slowly poisoned.

Don't use airstones in a daphnia culture. Use an open airline tube or a bio-foam filter (the latter contains an airstone inside in the apparatus, but the bubbles are not fine enough to harm the daphnia when the bubbles emerge into the tank. Note however, there should only be a weak flow of air through the filter to avoid too much water flow).

Don't add miracle grow, etc, directly to the culture. It won't be much use, and it could also poison the culture, in high concentrations.

Don't add fresh tap water to a daphnia culture unless you want to kill them all with the chlorine.

Don't keep your daphnia in the dark for days at a time as this can stimulate them to produce ephippia.

where do we get starter daphnia cultures?

[jest1081]

i usually bot mine from y618

[sly1984]

Very interesting thread... maybe they should pin up into articles, resources...

[Hershley]

Well written article bro ...

[jest1081]

not mine it was extracted from a site

[Ircknight]

Good effort. Thank for sharing.

[taizi]

they are good for fries imo ! worth to try ^^