AbstractWe have developed a short‐term, low‐cost method of detecting changes in the orientative ability ofDaphnia magnain response to xenobiotics. The method employs the reaction, a migration along the gradient, ofD. magnato a light intensity gradient. The method was derived from techniques established to simulate and analyze migration patterns of zooplankton in the natural environment. Each test uses a minimum of 100 1‐ to 3‐d oldDaphniaexposed to a directional light beam within a circular chamber. The chamber is divided into eight sections, each containing 45° of arc. These quadrants can be isolated from each other, thus isolating eight groups of migratingDaphnia.Each test results in three endpoints: an average direction for the migration (mean angle), an index of the magnitude of random, undirected migration (rvalue) and a percentage of nonresponse. The method was validated by showing a positive dose‐related response to a known neurotoxin, lindane. The method is sensitive to lindane, producing effects on orientation even at a concentration as low as 50 ppb. The effect of lindane was a dramatic increase in the random migration of dosedDaphnia, showing a less directed migration pattern than control. Implications of developing a behavioral test withDaphniaand its correlation with the natural environment are discussed, as well as its incorporation into the general toxicity screening strategy. Interpretative and comparative statistical analysis of the method's endpoints are presented and
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