Zebrafish germline development. a Fluorescence microscopy imaging of zebrafish kop-EGFP-F'-nos3-′UTR-cry-DsRed transgenic embryos at 4, 7, 24, and 36 hpf (h post fertilisation). b A schematic representation of stages of germline development in zebrafish. At the four-cell stage, germ plasm (red circles) localises to the four cleavage furrows. At 4 hpf (sphere), four clusters of primordial germ cells (PGCs) (red circles) are easily identifiable. In the gastrula stage embryo, four clusters of PGCs start to migrate dorsally. By the pharyngula stage, PGCs have completed their migration and are located between the 8th and the 10th somite