Mass Rearing of Daphnia magna for Insecticide Bioassay

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Abstract
Although the cladoceran Daphnia magna Straus, or water flea, is sensitive to a broad group of insecticides, a satisfactory rearing method for bioassay is necessary for its practical use. A method has been developed using wide-mouth gallon jars for immature animals. They are then transferred to another chamber consisting of a large plastic funnel which has a plastic stopcock fused to the stem. To the lower outlet of the stopcock is fused a plastic bottle cap which holds an 8-oz bottle. A plastic ridge inside and near the bottom of the funnel holds a plastic ring covered with a fine screen, causing the adults to remain in the funnel, while the young pass through the screen and down into the bottle in response to light. Production consistently averaged 600 young daily for 18 months using 5 of these chambers. This method requires about one-third the time of previous methods. Many possible foods were studied. Best results were obtained with a mixture of algae (Scenedesmus obliquus) and yeast. Several artificial waters have been investigated, the best of which failed to maintain the culture satisfactorily after 32 generations. Search for a satisfactory defined water continues. Artesian water is used presently for maintenance of the culture as it is less variable than pond, lake, stream, or river waters.