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Culture Techniques of Moina

This document is copyrighted by the University of Florida,
Institute of Food and Agricultural Sciences (UF/IFAS) for the people of
the State of Florida. UF/IFAS retains all rights under all conventions,
but permits free reproduction by all agents and offices of the Cooperative
Extension Service and the people of the State of Florida. Permission is
granted to others to use these materials in part or in full for
educational purposes, provided that full credit is given to the UF/IFAS,
citing the publication, its source, and date of publication.

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Culture Techniques of Moina: The Ideal Daphnia for Feeding
Freshwater Fish Fry1

R.
W. Rottmann2

Daphnia are small freshwater crustaceans commonly called "water
fleas". This common name is the result not only of their size, but their
short, jerky hopping movement in water. The genera Daphnia and
Moina are closely related cladocerans. They occur throughout the
world and are collectively known as daphnia.

Daphnia have a body consisting of a head and a trunk). The antennae
are the main means of locomotion. Large compound eyes lie under the skin
on the sides of the head. One of the major characteristics of daphnia is
that the main part of the body, the trunk, is enclosed in an external
skeleton (carapace). Periodically, they molt or shed their external
shell. The brood pouch, where the eggs and embryos develop, is on the
dorsal side of the female. In Daphnia , the brood pouch is
completely closed, while Moina have an open pouch.

There is
considerable size variation between the genera. Moina are
approximately half the maximum length of Daphnia . Adult Moina
(700 to 1,000µm) are longer than newly-hatched brine shrimp (500 µm)
and approximately two to three times the length of adult rotifers. Young
Moina (less than 400 µm), however, are smaller than newly-hatched
brine shrimp and approximately the same size or slightly larger than
adult rotifers. As a result, Moina are ideally suited for feeding
freshwater fish fry. The newly-hatched fry of most freshwater species
can ingest young Moina as their initial food. In addition, brine
shrimp die quickly in freshwater. In Singapore, Moina micrura
grown in ponds fertilized with mostly chicken manure or, less
frequently, with pig manure are used as the sole food for fry of many
ornamental tropical fish species, with 95 to 99% survival to 3/4 inch
(20 mm) in length quite common. Unfortunately, there is very little
information concerning practical mass culture methods of Moina ,
and the available information is in mimeograph documents, foreign
journals, or other scarce publications.

Physical and Chemical Requirements

Moina appear in high
concentrations in pools, ponds, lakes, ditches, slow-moving streams, and
swamps where organic material is decomposing. They become especially
abundant in temporary water bodies which provide them with suitable
conditions for only a brief period. Moina are generally quite
tolerant of poor water quality. They live in water where the amount of
dissolved oxygen varies from almost zero to supersaturation. Moina
are particularly resistant to changes in the oxygen concentration
and often reproduce in large quantities in water bodies strongly
polluted with sewage. Species of Moina have been reported to play
an important role in the stabilization of sewage in oxidation lagoons.
The ability to survive in oxygen-poor environments is due to their
capacity to synthesize hemoglobin. Hemoglobin formation is dependent on
the level of dissolved oxygen in the water. The production of hemoglobin
may also be caused by high temperature and high population density.

Moina are resistant to extremes in temperature and easily
withstand a daily variation of from 41 to 88°F (5 - 31°C); their optimum
temperature is 75 to 88°F (24 - 31°C). The high temperature tolerance of
Moina is of great advantage for both the commercial fish farmers
in the southern U.S. and hobbyists culturing live food at home.

Food Requirements

Moina feed on various groups of
bacteria, yeast, phytoplankton, and detritus (decaying organic matter).
Bacterial and fungal cells rank high in food value. Populations of
Moina grow most rapidly in the presence of adequate amounts of
bacterial and yeast cells as well as phytoplankton. Moina are one
of the few zooplankton which can utilize the blue-green algae
Microcystis aeruginosa . Both plant and animal detritus may
provide for the growth and reproduction of Moina . The food value
of detritus depends on its origin and diminishes with the age of the
detritus.

Life Cycles of Moina

The reproductive cycle of Moina
has both a sexual and asexual phase. Normally, the population
consists of all females that are reproducing asexually. Under optimum
conditions, Moina reproduce at only 4 to 7 days of age, with a
brood size of 4 to 22 per female. Broods are produced every 1.5 to 2.0
days, with most females producing 2 to 6 broods during their lifetime.

Under adverse environmental conditions, males are produced and sexual
reproduction occurs resulting in resting eggs (ephippia), similar to
brine shrimp eggs. The stimuli for the switch from asexual to sexual
reproduction in populations of Moira is an abrupt reduction in
the food supply, resulting in an increase in resting egg production.
However, it is advantageous to keep the population well fed and in the
asexual mode of reproduction, since fewer progeny are produced with
resting eggs.

High population densities of Daphnia can result in a dramatic
decrease in reproduction, but this is not apparently the case with
Moina . The egg output of Daphnia magna drops sharply at a
density as low as 95 to 115 mature individuals per gallon (25 - 30/ L).
The maximum sustained density in cultures of Daphnia reported is
1,900 individuals per gallon (500/ L). Moina cultures, however,
routinely reach densities of 19,000 individuals per gallon (5,000 /L)
and are, therefore, better adapted for intensive culture.

A comparison of the production of Daphnia magna and Moina
macrocopa
cultures fertilized with yeast and ammonium nitrate,
showed that the average daily yield of Moina (1.42 to 1.47 ounces
/ 100 gallons) (106 - 110 g/m 3 ) is three to four times the
daily production of Daphnia (0.33 to 0.53 ounces / 100 gallons)
(25 - 40 g/m 3 ). Moina cultures fed phytoplankton
cultured on organic fertilizer have been reported to exceed 5 ounces /
100 gallons (375 g/m 3 ) daily yield.

Nutritional Value of Moina

The nutritional content of
Moina varies considerably depending on their age and the type of
food they are receiving. Although variable, the protein content of
Moina usually averages 50% of the dry weight. Adults normally
have a higher fat content than juveniles. The total amount of fat per
dry weight is 20% to 27% for adult females and 4% to 6% for juveniles.

Procedure for Moina Culture

The batch culture method of
producing Moina uses a continuous series of cultures. Briefly, a
new culture is started daily in a separate container using the
procedures outlined below. When all the fungal, bacterial, and algal
cells are consumed, usually about 5 to 10 days after inoculation, the
Moina are completely harvested, and the culture is restarted.
This method is particularly applicable when a specific quantity of
Moina is needed each day, because daily production is much more
controlled. Batch culture is also useful for maintaining pure cultures
because there is less chance of the cultures becoming contaminated with
competitors (e.g., protozoans, rotifers, copepods) or predators of fish
larvae or fry (e.g., Hydra , back-swimmers, diving beetles,
dragonfly larvae).

Semi-continuous cultures can be maintained for two months or more by
daily partial harvests of Moina , water changes, and regular
feeding, keeping the population in a state of rapid growth. Eventually,
the Moina cultures will fail to respond to additional
fertilization. When it is evident that they are not reproducing well,
the Moina should be completely harvested and a new culture
started. Moina can be produced either in combination with their
food or as separate cultures. Combined culture is the simplest, but
production from separate cultures has been reported to be approximately
1/3 higher. For separate culture, the phytoplankton tank is positioned
so that it can be drained into the Moina culture tank. Production
from separate cultures has the disadvantage of requiring additional
space for the cultivation of phytoplankton. Consequently, production per
unit volume, especially in large scale cultures, is equivalent to when
the animals are grown together with their food. However, there are
advantages of separate culture of Moina and phytoplankton such
as: 1) less chance of contamination; 2) greater degree of control; and
3) more consistent yield.

  • Regardless of the culture method, always maintain several
    Moina cultures to ensure a supply in case of a die off.

Containers

Cultures have been maintained in 10-gallon (38-L)
aquaria. However, this volume is usually too small to yield enough
Moina to satisfy demand. Tanks or vats (concrete, stainless
steel, plastic, or fiberglass), and earthen ponds can be used. Wading
pools, plastic sinks, old bathtubs, discarded refrigerator liners, and
cattle watering troughs also work well. Do not use unpainted metal
containers unless they are stainless steel.

Water depth should be no greater than 3 feet (0.9 m). A maximum depth
of 16 to 20 inches (0.4 - 0.5 m) is probably optimum. The shallow water
depth allows good light penetration for photosynthesis by phytoplankton
and provides a large surface to volume ratio for oxygen diffusion.

Diffuse light or shade over 1/3 of the water surface of the Moina
culture container is recommended. A greenhouse covered with shade
cloth (50-80% light reduction) is ideal. Outdoor cultures should be
protected from rain to help stabilize production and screened to prevent
entry of predacious aquatic insects.

Containers to be used, whether aquaria, tanks, vats, or ponds, need
not be particularly clean. However, filamentous algae and predators of
fish larvae or fry (e.g., Hydra , back-swimmers, diving beetles,
dragonfly larvae) can be especially troublesome in Moina
cultures. Tanks can be disinfected with a 30% solution of muriatic
acid or by drying in sunlight. Earthen ponds should be drained and sun
dried.

Water

Moina are extremely sensitive to pesticides,
metals (e.g., copper and zinc, which may be prevalent in municipal or
well water), detergents, bleaches, and other toxic materials in the
water supply. Insure that toxins are not inadvertently introduced into
the culture container. Well water should be aerated for at least two
hours. Municipal water should be aerated for at least two days to
neutralize the chlorine, or sodium thiosulfate or a commercially
available chlorine neutralizer can be added to shorten this process.
Natural spring water is ideal. Rain water is also excellent for Moina
cultures, if it is collected from an area that does not have
excessive air pollution. Filtered lake or stream water may also be used.

The optimum water temperature for Moina is 75 to 88°F (24 -
31°C). Moina continue to thrive at temperatures in excess of 90°F
(32°C) for short periods. However, low temperatures reduce production.

Aeration

Gentle aeration of the Moina pools oxygenates
the water, keeps food particles in suspension, and increases
phytoplankton production; this results in an increase in the number of
eggs per female, the proportion of egg-bearing females in the
population, and the population density. A small trickle of fresh water
into the culture container may also improve production of Moina .
Only one or two aquarium air lines are required in culture containers up
to 400 gallons (1.5 m 3 ). Extremely small bubbles should be
avoided; they can get trapped under the carapace. This causes Moina
to float at the surface, eventually killing them.

Feeding or Fertilizing

Listed below are some common fertilizer
materials and application rates. Try several of these culture medias to
determine which works best in your situation. The initial fertilization
rates provided are only a starting point and will probably need to be
adjusted depending on individual culture conditions.

The following quantity of fertilizer materials should be added
initially for each 100 gallons (379 L) of water. Additional feed or
fertilizer, approximately 50 to 100% of the initial amount, should be
added about 5 days later.

  1. Yeast: 0.3 - 0.5 ounce (8.5 - 14.2 g) of baker's yeast.
  2. Yeast and mineral fertilizer: 0.3 - 0.5 ounce (8.5 - 14.2 g) of
    yeast, and 0.5 ounce (14.2 g) of ammonium nitrate.
  3. Alfalfa, bran, and yeast: 1.5 ounces (42.5 g) of alfalfa pellets
    or meal, 1.5 ounce (42.5 g) of wheat or rice bran, and 0.3 ounces (8.5
    g) of yeast.
  4. Cow manure or sewage sludge, bran, and yeast: 5 ounces (142 g) of
    dried manure or sewage sludge, 1.5 ounces (42.5 g) of wheat or rice
    bran, and 0.3 ounces (8.5 g) of yeast.
  5. Cow manure or sewage sludge, cotton seed meal, and yeast: Use 5
    ounces (142 g) of dried manure or sewage sludge, 1.5 ounce (42.5 g) of
    cotton seed meal and 0.3 ounces (8.5 g) of yeast.
  6. Horse or cow manure or sewage sludge: Combine 20 ounces (567 g) of
    dried manure or sewage sludge.
  7. Chicken or hog manure: Combine 6 ounces (170 g) of dried manure.
Organic fertilizers are usually preferred to mineral
fertilizers because they provide bacterial and fungal cells and detritus
as well as phytoplankton as food for the Moina . This variety of
food items more completely meets their nutritional needs, resulting in
maximum production. Mineral fertilizers may be used alone; however, they
work better in earthen ponds than in tanks or vats.

Fresh manures are preferred because they are richer in organic matter
and bacteria. However, some farm animals are given feed additives that
control fly larvae in their manure; these may inhibit the production of
Moina . Although not absolutely necessary, the manure is
frequently dried before use. Commercially available organic fertilizers
such as dehydrated cow manure and sewage sludge may be used for Moina
cultures.

Although manure is widely used to culture Moina , yeast,
alfalfa, and bran are less objectionable to use and work well. Activated
yeast (baker's yeast) is readily available from wholesale food
distributors in 2-pound (0.9-kg) bags. Bran and alfalfa meal or pellets
can be purchased in 50-pound (22.7-kg) bags from livestock feed stores.

Coarse organic materials such as manure, sewage sludge, hay, bran,
and oil seed meals are usually suspended in the water column in mesh
bags. Cheese cloth, burlap, muslin, nylon, or other relatively loose
weave fabrics may be used. Nylon and other synthetic fabrics, however,
do not deteriorate in water as do cotton or burlap. For smaller culture
containers, nylon stockings work well for this purpose: they are
inexpensive, and readily available. The use of a bag prevents large
particles from being a problem when the Moina are harvested and
allows greater control of fertilization.

Overfeeding can quickly cause problems in water quality. Regardless
of the type of media used, start with small amounts of feed or
fertilizer added at frequent intervals; slowly increase the amount used
as you gain experience. If fungus occurs in the culture container due to
over-fertilization, the bag containing the organic material should be
removed from the culture. If fungus persists in large quantities, the
culture should be discarded and restarted.

Excessively high pH (greater than 9.5) due to a heavy algae bloom and
the resulting increase in the proportion of the toxic form of ammonia
(un-ionized), may inhibit the production of Moina . The pH of the
culture can be adjusted to 7 to 8 with vinegar (acetic acid).

Inoculating

Use pure live cultures to inoculate. Avoid using
animals for inoculation from poor or declining cultures, cultures
producing resting eggs, or cultures containing predators of fish larvae
or fry. Inoculate with approximately 100 Moina / gallon (25/ L).
Although a culture can theoretically be started with a single female,
always use an adequate number to develop a harvestable population
quickly. If fewer are used, the population in the culture will increase
more slowly, therefore, the initial quantity of fertilizer or food
should be reduced to prevent overfeeding. A greater number used for
inoculation reduces the time to harvesting and lessens the chance of
contamination by competitors. Cultures are usually inoculated 24 hours
or more after fertilization. However, when yeast is used, Moina
can be added to the culture after a few hours of aeration, assuming
good water quality and proper temperature. This is because the yeast
cells are immediately available to the Moina as food. The small
amount of phytoplankton present in the water and digestive tract of the
Moina used to inoculate the culture is usually sufficient to
initiate a phytoplankton bloom. Sometimes the mortality of the initial
inoculation is high and an additional inoculation is required.

Monitoring

The culture should be inspected daily to determine
its health. The following observations should be made.

  • The health of the culture is determined by stirring the culture,
    removing 1 tablespoon (15 ml) of the culture, and examining the sample
    with a 8X to 10X hand lens or dissecting scope. Green or brown-red
    Moina with full intestinal tracts and active movement indicate
    a healthy culture. Pale Moina with empty digestive tracts or
    Moina producing resting eggs are indications of suboptimum
    environmental conditions or insufficient food.
  • The population density of Moina is determined by killing
    the Moina in the sample with a 70% alcohol solution and
    counting all Moina in a petri dish with a hand lens or
    dissecting scope. Cultures ready for harvest should contain 45 to 75
    Moina in the 1-tablespoon sample (3 to 5/ml). With experience,
    population density can be estimated visually without the need for
    counts.
  • The food concentration in the culture water, when examined in a
    clear glass, should appear slightly cloudy and tea colored or green.
    Clear culture water is an indication of insufficient food. The
    cultures should be fed or fertilized with approximately 50-100% of the
    initial quantity whenever the transparency is greater than about 12 to
    16 inches (0.3 to 0.4 m). This can be determined with a white plastic
    or metal lid approximately 4 inches (100 mm) in diameter, attached to
    the end of a yard stick. The depth of transparency is where the disk
    is just barely visible when lowered into the tank.
  • If predators of fish larvae or fry (e.g., Hydra ,
    back-swimmers, diving beetles, dragonfly larvae) are observed, discard
    the culture and clean and disinfect the tank or pool to avoid
    contaminating other cultures.

Harvesting

Moina can be harvested by simply dipping out
the required number with a brine shrimp net or re-usable coffee filter
as they concentrate in "clouds" at the surface. Cultures may also be
harvested by draining or siphoning the culture water into a plankton
collector equipped with 50 to 150-µm mesh netting net suspended in a
container of water. Turn off the aeration and allow the food particles
to settle before harvesting. For semi-continuous culture, do not harvest
more than 1/5 to 1/4 of the population each day, unless you are
restarting the culture. Harvesting by draining the culture tank allows
for a partial water exchange, improving water quality. Harvest only
small quantities at a time and transfer the Moina to containers
with fresh water to keep them alive.

The bottom sediments should be stirred up manually every day
following harvest, thoroughly mixing the culture, to prevent anaerobic
conditions and re-suspend food particles.

Additional points

Differences in size, brood production, and
optimum environmental conditions exist between different species and
varieties of Moina . Adjustments will need to be made in the
culture technique depending on the particular species or variety you
wish to produce.

Additional surfaces in the culture tank may have a positive effect on
the production of Moina . For Daphnia , a four-fold
increase of surface area, in the form of plastic sheets, has been shown
to result in a four-fold increase in the density, biomass, and harvest.
It is unknown whether this is the result of improved water quality due
to nitrifying bacteria on the substrate, a change in the spatial
distribution of the Daphnia , or improved nutrition.

It may not always be possible to match Moina production to the
food demand of the fish fry. Harvested Moina can be kept alive
for several days in clean water in a refrigerator. They will resume
normal activity when they are again warmed. The nutritional quality of
the stored Moina probably will not be optimal because of the
period of starvation, so the Moina should be enriched with algae
and yeast before feeding them to fish. Moina can be stored for
long periods by freezing in low salinity water (7 ppt, 1.0046 density)
or by freeze-drying. Both methods kill the Moina , so adequate
circulation is required to keep them in suspension after thawing so they
will be available to the fish fry. Frozen and freeze-dried Moina
are not as nutritious as live animals, and they are not as readily
accepted by fish fry. Although freezing or freeze-drying does not
significantly alter the nutritional content of Moina , nutrients
do leach out rapidly into the water. Nearly all of the enzyme activity
is lost within ten minutes after introduction in fresh water. After one
hour, all of the free amino acids and many of the bound amino acids are
lost.

Sources of Moina

Elwyn Segrest
Segrest Farms

P.O. Box 758
Gibsonton, FL 33534
(813) 677-9196


Footnotes

1.This document is Circular
1054, one of a series of the Deparment of Fisheries and Aquatic
Sciences, Florida Cooperative Extension Service, Institute of Food and
Agricultural Sciences, University of Florida. May, 1992. Please visit
the FAIRS Web site at http://hammock.ifas.ufl.edu.

2.R. W. Rottmann, Senior Biological
Scientist, Department of Fisheries and Aquatic Sciences, Cooperative
Extension Service, Institute of Food and Agricultural Sciences,
University of Florida, Gainesville, 32611.


The Institute of Food and Agricultural Sciences is an equal
opportunity/affirmative action employer authorized to provide research,
educational information and other services only to individuals and
institutions that function without regard to race color, sex, age,
handicap, or national origin. For information on obtaining other
extension publications, contact your county Cooperative Extension
Service office.

Florida Cooperative Extension Service /
Institute of Food and Agricultural Sciences / University of Florida /
Christine Taylor Waddill, Dean



Copyright Information

This document is copyrighted by the
University of Florida, Institute of Food and Agricultural Sciences
(UF/IFAS) for the people of the State of Florida. UF/IFAS retains all
rights under all conventions, but permits free reproduction by all
agents and offices of the Cooperative Extension Service and the people
of the State of Florida. Permission is granted to others to use these
materials in part or in full for educational purposes, provided that
full credit is given to the UF/IFAS, citing the publication, its source,
and date of publication.
href="http://edis.ifas.ufl.edu/BODY_FA024">Original source of
article:  "http://edis.ifas.ufl.edu/BODY_FA024"