To culture efficiently Moina macrocopa with the recirculating zooplankton culture device, optimal culture conditions in closed environment have to be investigated thoroughly. Optimal conditions at food, temperature or quality of water have been defined, however, few reports have been publised on flow speed or direction. Therefore, the system for culture experiment in fixed flow which has three airtight rearing cells had been organized, and influences of flow rate or direction on population

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... h were investigated. In these experiments, M. macrocopa increased efficiently at slow flow speed, 10 cm/min, and the flow directions hardly influenced to the population growths. To control flow rates should be effective for the efficient culture of M. macrocopa.