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		Culture Techniques of Moina: The Ideal Daphnia for Feeding Freshwater Fish Fry
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		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 over-feeding. 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. 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 a 1-teaspoon (3­5/ml) 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 45­75 Moina in the 1-teaspoon sample (3­5/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 50­100% of the initial quantity whenever the transparency is greater than about 12­16 inches (0.3­0.4 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 20­25% 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 re-suspend food particles and prevent anaerobic conditions from developing. more...

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