The parasiticide ivermectin is widely used due to its high efficiency against endo- and ectoparasites in livestock. Local aquatic ecosystems can thus be contaminated, but few data are available to quantify chronic effects of ivermectin on non-target aquatic organisms. The aim of our study is to understand how ivermectin affects survival, growth and reproduction of two cladoceran species: Daphnia magna (one Japanese and one European strain) and Ceriodaphnia dubia. Hence, chronic toxicity tests were carried out. Survival and the number of neonates per litter were daily recorded, and adult length was measured at the end of the test. The first data analyses showed that ivermectin had a significant effect on all processes, but that differences occurred between species and between strains. The European strain of D. magna was more sensitive than the Japanese one, and the effects appeared earlier but were lower for C. dubia than D. magna.