Genetically modified (GM) maize expressing the Bt-toxin Cry1Ab (Bt-maize) was tested for effects on survival, growth, and reproduction of the water flea <i>Daphnia magna</i>, a crustacean arthropod commonly used as a model organism in ecotoxicological studies. In three repeated experiments, <i>D. magna</i> were fed 100% ground maize in suspension, using either GM or isogenic unmodified (UM) maize. ...