Laboratory-bred males of three-spined sticklebacks (Gasterosteus aculeatus) were assigned to one of two treatments: exposure to the nematode parasite Camallanus lacustris (exposed) or control (i.e. unexposed). After infection key fitness and immune traits were measured. Fish were then sacrificed and liver tissue was dissected. Reduced representation bisulfite sequencing was conducted on DNA extracted from whole liver tissue. Overall we aimed to investigated the role of host DNA methylation modifications to respond to parasite infections.