Daphnia FAQ - Prototype

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May 10, 1996, 3:00:00 AM5/10/96
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Daphnia FAQ - Prototype

Having seen many questions about Daphnia, I have decided
to create a FAQ for Daphnia culture. It is by no means the
definitive source, and will be expanded on in the future. I have
gathered this information from various books and publications.
Unlike my experiences with Artemia, I have very little
practical experience in raising these guys, in fact, I have only
just set up a tank dedicated to Daphnia. I have tried extremely
hard to make sure I put everything in my own words so as not
to plagiarize. If you recognize a sentence here and there, its
because there really isnt a better way to say it. There is a
wealth of information out there that gets real scientific, or
pertains to large pond culturing operations that require many
pounds if Daphnia per day. Much of this I have left out as it
really doesnt pertain to our goal of growing these critters.
Anyway, here it is, hope you find it to be of use.
Any comments, suggestions or items you would like to see
included should be forwarded to me, Kai Schumann
(K...@Lilly.com)

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 - Daphnia 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.

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