Salinity is increasing in aquatic ecosystems in the Mediterranean region due to global change, and this is likely to have an important impact on host-parasite interactions. Here the relationships between infection by ectoparasitic water mites and salinity variation, on survival and fecundity of water boatmen Corixidae from Doñana National Park was studied in the laboratory. Larvae of Sigara lateralis parasitised by larval mites (Hydrachna skorikowi) had lower survivorship, and failed to moult to the adult stage. In adult corixids (S. lateralis and Corixa affinis) fitness was reduced at high salinities and in individuals infected by H. skorikowi, both in terms of survival and fecundity. Evidence was also found for parasitism-salinity interactions. Results suggest that ongoing increases in salinity in Mediterranean ponds due to climate change and water abstraction for agriculture or urban use have a strong impact on water bugs, and that their interactions with ectoparasites may modify salinity effects. informacion[at]ebd.csic.es: Céspedes et al (2019) Water boatman survival and fecundity are related to ectoparasitism and salinity stress. PLos ONE. Doi 10.1371/journal.pone.0209828