Updated project metadata. Ichthyophthirius multifiliis is a ciliated protozoan parasite recognized as one of the most pathogenic diseases of wild and cultured freshwater fish. Fish skin mucus plays a significant role against invading pathogens. However, the protein-based modulation against infection with I. multifiliis, of host fish at this barrier is unknown. The aim of this study was to investigate the modulation of the skin mucus after infection with I. multifiliis using quantitative proteomics to provide insights into the post-transcriptional and post-translational regulation of skin mucus proteins. Thus, we investigated the skin mucus proteome of common carp (Cyprinus carpio) using a shotgun proteomic approach at days 1 and 9 after I. multifiliis exposure.