While the decrease in human sperm count in response to pollutants is a worldwide concern, little attention is being devoted to its causes and occurrence in the biodiversity of the animal kingdom. Arthropoda is the most species-rich phyla, inhabiting all aquatic and terrestrial ecosystems. During evolution, key molecular players of the arthropod endocrine system have diverged from the vertebrate counterparts. Consequently, arthropods may have different sensitivities toward endocrine disrupting chemicals (EDCs). Here alteration of sperm quality in a crustacean, Gammarus fossarum, a popular organism in freshwater risk assessment, was investigated after laboratory exposure to various concentrations of three different xenobiotics: cadmium, methoxyfenozide, and pyriproxyfen. The integrity of the reproductive process was assessed by means of sperm-quality markers. For each substance, semiquantitative/relative proteomics based on spectral counting procedure was carried out on male gonads to observe the biological impact. The changes in a total of 871 proteins were monitored in response to toxic pressure. A drastic effect was observed on spermatozoon production, with a dose-response relationship. While exposure to EDCs leads to strong modulations of male-specific proteins in testis, no induction of female-specific proteins was noted. Also, a significant portion of orphans proved to be sensitive to toxic stress.