A recent study in the zebrafish Danio rerio showed that changes in the social environment, and specifically in the intensity of sperm competition, do not only lead to modifications in sperm motility and sperm velocity, the paternally experienced environment of sperm competition also translates into differences in hatching timing and larval survival (Zajitschek et al, 2014). The aim of my PhD project is to assess where in the sperm the trigger for this mechanism lies (RNA vs. chromatin structure vs. methylation processes) and how this is transferred into the offspring. I am investigating the role of sperm in parental effects and aim to identify potential mechanisms causing paternal effects (i.e. sperm-mediated epigenetic mechanisms). This involves two experiments in particular - one to actually isolate RNA from sperm and create a transcriptome for the zebrafish ejaculate, which can then be used as a reference for the entire project. In a second step, I perform experiments to manipulate the paternal effects and look into the underlying molecular mechanisms. I assess the causes for variation in epigenetic effects in males by manipulating for example, sperm competition levels among males and comparing the epigenetic patterns in their sperm for which I use three different approaches, i.e. (A) comparing the RNA profile in sperm (B) investigating chromatin structures in sperm and (C) determining the methylation patterns in sperm. Experimental tools such as in vitro fertilisation and experimental manipulation are combined with transcriptomics and epigenomics to address these two questions using a model organism.