The processes of aging are incredibly complex and still somewhat unclear; however, epigenetic features such as DNA methylation, are beginning to emerge as key markers of the aging process and may constitute a “biological clock”. Biological clocks have been the interest of research for some time, and have included telomere length, microsatellite mutations, and tumor suppression gene expression. Nevertheless, DNA methylation clocks appear to be surprisingly accurate, predicting biological age in a wide variety of human cell and tissue types (Horvarth, 2013). Use of methylation clocks could become a standard diagnostic tool for early detection of age-related disease; however, current progress in this area is hampered by the lack of an appropriate model system. In addition to human health, a DNA methylation-based biological clock would be valuable in other model and non-model species, especially in species where age might otherwise be unknown and/or difficult to predict. We aim to produce a DNA-methylation clock for zebrafish (Danio rerio), using next-generation bisulfite sequencing, for males aged between 4 and 28 months. Recently, researchers have demonstrated an overall decrease in DNA methylation of somatic cells using a candidate gene approach in zebrafish, but a pattern of hypermethylation in the male germ line with increasing age, which is also in line with our preliminary findings for young vs. old males. Determining a DNA methylation-based biological clock in zebrafish will have wide-ranging implications, as zebrafish are a frequently used model organism in aging studies.