Article Daphnia

This was written 15years ago and is in my archives
rick


Background
Daphnia are small freshwater crustaceans that may also be known as water fleas. They are called this because of their short jerky hopping movement through the water. There are many species of Daphniidae and their distribution is world wide. Of all the species, the genera of Daphnia and Moina are the most diverse, and are a major food source for both young and adult freshwater fish. In the orient Moina is the species of Daphniidae most used in fish culture.
Size
There is a big size difference in the Daphniidae, depending on the species. Newly hatched Moina are slightly larger than newly hatched brine shrimp, and twice as big as average adult rotifers, but newly hatched Daphnia are twice as big as Moina, and may not be suitable for some of the smaller fish fry because of their size.
Life cycle of Daphnia
The daphnia has both sexual and asexual phases. In most environments, the population consists entirely of females that reproduce asexually. Under optimum conditions, a female may produce more than 100 eggs per brood, repeating every 3 days. A female may have as many as 25 broods in its lifetime, but the average is about 6. The female will start to reproduce at about 4 days old with a brood size of 4 to 22 eggs. Under adverse conditions, males are produced, and sexual reproduction begins. The result is the laying of resting eggs, just like the brine shrimp. Factors that can trigger this are a lack of food, low oxygen supply, a high population density, or low temperatures.
Nutritional Value
The nutritional content of Daphnia varies with age, and what its been eating. The protein content is usually around 50% of dry weight. Quite the opposite from Artemia, adults normally have a higher fat content than juveniles, about 20-27% for adults, and 4-6% for juveniles. Some species have been reported to have protein contents exceeding 70%. Live Moina are about 95% water, 4% protein, 0.54% fat, 0.67% carbohydrates, and 0.15% Ash. The fatty acid composition of food is important to the survival and growth of fish fry. Omega-3 highly saturated fatty acids are essential for many species of fish. Moina cultured on bakers yeast are high in monoenoic fatty acids. By using what is called w-yeast (yeast enriched with cuttlefish oil), Moina will contain very high levels of Omega-3 fatty acids. Moina can take up lipids very easily from the emulsion, but there is a side effect to this, apparently it also slows productivity, so this emulsion should only be fed to a batch separate from the main growout colony. Commercial formulas are available in pet supply houses for the enrichment of Artemia, Rotifer, and Daphnia cultures.
Physical Requirements
Salinity

are typically freshwater organisms, but, some are found in slightly brackish 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.
pH and ammonia

A pH between 6.5 and 9.5 is acceptable. High ammonia levels, with high pH will drastically reduce 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.
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 ppm 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-chlor 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. Municipal and well water may be contaminated enough to kill the culture. The best source of water is filtered stream or lake water, rain water collected from low air polluted areas, or, use the water from your aquarium water changes. Never use distilled or DI water, as it does not have the minerals needed for growth.
Temperature

Daphnia have a wide tolerance to temperature. The optimum temperature for Daphnia Magna is 18-22 deg C (64-72 F) Moina withstand extremes even more, resisting daily variations of 5-31 deg C (41-88 F); their optimum being 24-31 deg C (75-88 F). The higher temperature tolerance of Moina make this species a better choice where temperatures may rise above the comfort levels for Magna at certain times of the year.
Your culturing Tank
Continuous cultures can be maintained in two liter bottles, and for many aquarists, this is all that will be needed, but, usually the best culture tank is the good old ten gallon aquarium. No matter what you use, a shallow tank with a high surface area is best, and if you use a metal container, only stainless may be used. The use of a growlite bulb on a timer makes it easy to keep indoors. Gentle aeration is required, but fine bubbles should be avoided, as they catch under the carapace of the animals, floating them to the surface where they die. One trick to maintaining alot of green water, and not much hair algae was given to me by David Webb, thats to use rams horn or pond snails in the tank, they eat all the macro algae, and the micro algae is all that can get a decent foothold in the tank.
Care and Raising
Feeding the culture

Like Artemia, Daphnia feed on various groups of bacteria, yeast, microalgae, detritus, and dissolved organic matter. Bacteria and fungal cells are high in food value, but all foods rank second to microalgae. A good algae culture is vital to growing these guys, so if you set out to do everything you can to growing a flourishing algae culture you will be ensured success. A barrel or tank outside that gets plenty of sun virtually guarantees explosive algae growth. Moina is one of the few Zooplanktons that can utilize the bluegreen algae, but other algae must be present also for best growth. Organic fertilizers are preferred over the mineral varieties because they promote bacterial, fungal cells, detritus, and other nutrients that the Daphnia feed on. Fresh organic fertilizers are preferred over old or aged sources because they are richer in microbes and organic matter. This especially applies to manure, which is usually dried before use. Some farm animals are fed antibiotics and other additives that may inhibit Daphnia growth and should be avoided. Drying or other processing of these manures lessens the potency of these drugs. The cow manure sold at garden supply houses can be used with success if fresh manure is not available. Possibly the best fertilizer there is, is dried, processed sewage sludge, which is an excellent and consistent nutrient source. The fertilizer can be added to your culture in several ways. One is to soak the dry material for several hours, then distribute the wet material over the bottom, allowing it to slowly deteriorate. Another is to place the dry material (5-6 oz.) in a mesh bag (panty hose or cheese cloth) and suspend the bag inside the tank near an air supply for circulation and slow leaching, change every five days. An excellent source for this cheese cloth can be had at virtually any sporting goods store that sells hunting equipment, these large game bags are used to cover skinned game animals. The third is to soak the material for weeks until it decomposes into a nutrient slurry, then drip the liquid into the tank at a rate of 16 fl. oz. every five to eight days. Of the three, the last two are the cleanest methods tank wise. with the third method being the best. If you are doing this inside the house, or lucky you, you have a basement, you may have a problem with other family members complaining of the smell from your fermenting sewage factory. Luckily, you will not have to visit judge Wapner, or divorce court, because there is another way to feed these guys without the rank smell. Like Artemia, Daphnia will feed on Yeast (Brewers is best), bran, wheat flour, and dried blood. With the exception of activated yeast, care must be taken not to over feed with these foods as they will foul the water in short order. If you should decide to use these feeds, your culture will be healthier if you toss in some nice green algae water, obtained from a remote source, every week or so. If you feed yeast to a ten gallon culture, feed 0.3-0.5 oz. of yeast every five days.
Harvesting

A partial harvest every day is required to keep the culture healthy and productivity high. The harvest should not be more than 1/4 of the population daily, but the harvest may vary according to the quality of the population. The Daphnia can be harvested by simply netting them out of the container, or siphoning them into a net. When you stop the aeration, and let the tank settle, the Daphnia will concentrate on the surface where they are easy to harvest. An alternative is to drain 1/4 of the tank into a net, and replace the water with new fertilized water. This benefits you in two ways, first is it takes care of the feeding, and second it keeps the tank clean. Harvested Daphnia can be kept alive for several days in the refrigerator in clean water. They will resume normal activity when the water warms up. The nutritional quality will not be as good because they have been starving for several days, so a supplemental feeding is required for best effect. Daphnia can be stored for long periods by freezing them in a low salinity water (7ppt, 1.0046 density). Of course this kills the Daphnia, so adequate circulation is required to keep them in suspension during feeding. They also will not be as nutritious as the nutrients rapidly leach out in the aquarium. Nearly all the enzyme activity is lost in ten minutes, and in an hour all free amino acids, and most bound amino acids are lost. Fish will not feed on frozen Daphnia as readily either.
Trouble Shooting
Culture failed completely

Toxic materials in the water. Daphnia are extremely sensitive to pesticides, metals, detergents, and bleaches. Over fertilization with a mineral based fertilizer can also be toxic to the culture.
Slow Reproduction

Temperature is outside optimum range, insufficient dissolved oxygen because of dense colony. Heavy aeration, or fine bubbles can strip Daphnia from the culture. Overfeeding and fouling of the water. pH is too high due to algae bloom and the resulting increase in unionized ammonia. Insufficient food or fertilizer.