The toxicity of an organotin pesticide, triphenyltin hydroxide, was assessed with several freshwater cladoceran species. Daphnia pulex, Daphnia magna, and Ceriodaphnia dubia were exposed for 48 h to triphenyltin hydroxide in static acute toxicity tests. Values of the 48-h trimmed Spearman-Karber EC50s for the three species were found to be 14-5, 16-5, and 11-3 microg/l, respectively. Analysis of variance performed on EC50 values of replicates revealed no significant differences between the three species. Methods were employed which decrease animal handling stress and increase the accuracy and precision of the concentrations. (Copyright (c) 1989 Elsevier Science Publishers Ltd.)